From 2a8830f9f46d71fc7ce1ea45a5df8e074e2cf019 Mon Sep 17 00:00:00 2001
From: wpbonelli <wbonelli@ucar.edu>
Date: Fri, 29 May 2026 03:40:11 -0700
Subject: [PATCH 1/4] upgrade devtools

---
 flopy4/mf6/codec/filters.py                  |  11 +-
 flopy4/mf6/codec/reader/grammar/__init__.py  |   6 +-
 flopy4/mf6/codec/reader/grammar/filters.py   |  30 +--
 flopy4/mf6/codec/reader/transformer/typed.py |  40 ++--
 flopy4/mf6/converter/egress/unstructure.py   |   3 +-
 flopy4/mf6/spec.py                           |  28 ++-
 flopy4/mf6/utils/codegen/filters.py          | 225 ++++++++++---------
 flopy4/mf6/utils/codegen/generate_classes.py |   2 +-
 flopy4/mf6/utils/codegen/make.py             | 149 ++++++------
 flopy4/mf6/utils/codegen/overrides.py        |   7 +-
 pixi.lock                                    |  88 +++++---
 test/test_mf6_codegen.py                     |  80 +++----
 test/test_mf6_grammar_gen.py                 |  31 ++-
 test/test_mf6_reader.py                      |  45 ++--
 14 files changed, 394 insertions(+), 351 deletions(-)

diff --git a/flopy4/mf6/codec/filters.py b/flopy4/mf6/codec/filters.py
index 7db96bd6..8eefd829 100644
--- a/flopy4/mf6/codec/filters.py
+++ b/flopy4/mf6/codec/filters.py
@@ -3,15 +3,12 @@
 from typing import Any
 
 import xarray as xr
-from modflow_devtools.dfns.schema.field import Field
-from modflow_devtools.dfns.schema.v2 import FieldType
+from modflow_devtools.dfn.schema import FieldType
 
 
 def field_type(value: Any) -> FieldType:
     """Get a value's type according to the MF6 specification."""
 
-    if isinstance(value, Field):
-        return value.type
     if isinstance(value, bool):
         return "keyword"
     if isinstance(value, int):
@@ -20,7 +17,11 @@ def field_type(value: Any) -> FieldType:
         return "double"
     if isinstance(value, str):
         return "string"
-    if isinstance(value, (dict, tuple)):
+    if isinstance(value, tuple):
+        return "record"
+    if isinstance(value, dict):
+        if type_ := value.get("type", None):
+            return type_
         return "record"
     if isinstance(value, xr.DataArray):
         if value.dtype == "object":
diff --git a/flopy4/mf6/codec/reader/grammar/__init__.py b/flopy4/mf6/codec/reader/grammar/__init__.py
index 17e6aab5..8280d5f5 100644
--- a/flopy4/mf6/codec/reader/grammar/__init__.py
+++ b/flopy4/mf6/codec/reader/grammar/__init__.py
@@ -58,10 +58,10 @@ def make_grammar(dfn: Dfn, outdir: PathLike):
     outdir = Path(outdir).expanduser().resolve().absolute()
     env = _get_env()
     template = env.get_template("component.lark.jinja")
-    target_path = outdir / f"{dfn.name}.lark"
-    blocks, fields = _get_template_data(dfn.blocks)
+    target_path = outdir / f"{dfn['name']}.lark"
+    blocks, fields = _get_template_data(dfn["blocks"])
     with open(target_path, "w") as f:
-        name = dfn.name
+        name = dfn["name"]
         f.write(template.render(name=name, blocks=blocks, fields=fields))
 
 
diff --git a/flopy4/mf6/codec/reader/grammar/filters.py b/flopy4/mf6/codec/reader/grammar/filters.py
index 6eac2187..75e8cc22 100644
--- a/flopy4/mf6/codec/reader/grammar/filters.py
+++ b/flopy4/mf6/codec/reader/grammar/filters.py
@@ -1,12 +1,12 @@
 from collections.abc import Mapping
 
-from modflow_devtools.dfns.schema.v2 import FieldV2
+from modflow_devtools.dfn.schema import Field
 
 
-def field_type(field: FieldV2) -> str:
-    match field.type:
-        case t if t in ["string", "integer", "double"] and field.shape:
-            if "period" in field.block:
+def field_type(field: Field) -> str:
+    match field["type"]:
+        case t if t in ["string", "integer", "double"] and field.get("shape", None):
+            if "period" in field["block"]:
                 return "list"
             return "array"
         case "keyword":
@@ -14,17 +14,17 @@ def field_type(field: FieldV2) -> str:
         case "union":
             return ""  # keystrings generate their own union rules
         case _:
-            return field.type
+            return field["type"]
 
 
-def record_child_type(field: FieldV2) -> str:
+def record_child_type(field: Field) -> str:
     """
     Get the grammar type for a field within a record context.
 
     In records, string fields should use 'word' instead of 'string'
     to avoid consuming the rest of the line (since string matches token+ NEWLINE).
     """
-    match field.type:
+    match field["type"]:
         case "string":
             return "word"  # Use word for strings in records to match single tokens
         case t if t in ["double", "integer"]:
@@ -34,21 +34,21 @@ def record_child_type(field: FieldV2) -> str:
         case "union":
             return ""  # unions generate their own union rules
         case _:
-            return field.type
+            return field["type"]
 
 
-def is_period_list_field(field: FieldV2) -> bool:
+def is_period_list_field(field: Field) -> bool:
     """Check if a field is part of a period block list/recarray."""
-    if not field.shape or not field.block:
+    if not field.get("shape", None) or not field.get("block", None):
         return False
     return (
-        "period" in field.block
-        and field.type in ["string", "integer", "double"]
-        and field.shape is not None
+        "period" in field["block"]
+        and field["type"] in ["string", "integer", "double"]
+        and field["shape"] is not None
     )
 
 
-def group_period_fields(block_fields: Mapping[str, FieldV2]) -> dict[str, list[str]]:
+def group_period_fields(block_fields: Mapping[str, Field]) -> dict[str, list[str]]:
     """
     Group period block fields that should be combined into a single list.
 
diff --git a/flopy4/mf6/codec/reader/transformer/typed.py b/flopy4/mf6/codec/reader/transformer/typed.py
index ac2e5fa1..a59ee6d0 100644
--- a/flopy4/mf6/codec/reader/transformer/typed.py
+++ b/flopy4/mf6/codec/reader/transformer/typed.py
@@ -4,7 +4,7 @@
 import numpy as np
 import xarray as xr
 from lark import Token, Transformer
-from modflow_devtools.dfn import Dfn
+from modflow_devtools.dfn import Dfn, get_fields
 
 from flopy4.utils import parse_number
 
@@ -15,8 +15,8 @@ class TypedTransformer(Transformer):
     def __init__(self, visit_tokens=False, dfn: Dfn = None):
         super().__init__(visit_tokens)
         self.dfn = dfn
-        self.blocks = dfn.blocks if dfn else None
-        self.fields = dfn.fields if dfn else None
+        self.blocks = dfn["blocks"] if dfn else None
+        self.fields = get_fields(dfn) if dfn else None
         # Create a flattened fields dict that includes nested fields
         self._flat_fields = self._flatten_fields(self.fields) if self.fields else None
 
@@ -32,13 +32,13 @@ def _flatten_fields(self, fields: dict) -> dict:
         """Recursively flatten fields dict to include children of records and unions."""
         flat = dict(fields)  # Start with top-level fields
         for field in fields.values():
-            if hasattr(field, "children") and field.children:
+            if "children" in field and field["children"]:
                 # Add children fields
-                for child_name, child_field in field.children.items():
+                for child_name, child_field in field["children"].items():
                     flat[child_name] = child_field
                     # Recursively flatten nested children
-                    if hasattr(child_field, "children") and child_field.children:
-                        nested_flat = self._flatten_fields(child_field.children)
+                    if "children" in child_field and child_field["children"]:
+                        nested_flat = self._flatten_fields(child_field["children"])
                         flat.update(nested_flat)
         return flat
 
@@ -143,7 +143,7 @@ def string(self, items: list[Any]) -> str:
             return value.strip("\"'")
         else:
             # It's a tree, extract the token value
-            return str(value.children[0]) if hasattr(value, "children") else str(value)
+            return str(value["children"][0]) if hasattr(value, "children") else str(value)
 
     def simple_string(self, items: list[Any]) -> str:
         """Handle simple string (unquoted word or escaped string)."""
@@ -197,7 +197,7 @@ def record(self, items: list[Any]) -> list[Any]:
                 token_child = item.children[0]
                 if hasattr(token_child, "children") and len(token_child.children) > 0:
                     # This is a number tree, get the actual value
-                    values.append(token_child.children[0])
+                    values.append(token_child["children"][0])
                 else:
                     # This is a direct value (string)
                     values.append(token_child)
@@ -270,14 +270,14 @@ def __default__(self, data, children, meta):
             field_name, alternative_name = parts
             if (parent_field := self._flat_fields.get(field_name, None)) is not None:
                 if (
-                    parent_field.type == "union"
-                    and hasattr(parent_field, "children")
-                    and parent_field.children
-                    and alternative_name in parent_field.children
+                    parent_field["type"] == "union"
+                    and "children" in parent_field
+                    and parent_field["children"]
+                    and alternative_name in parent_field["children"]
                 ):
                     # This is a union alternative
-                    alt_field = parent_field.children[alternative_name]
-                    if alt_field.type == "keyword":
+                    alt_field = parent_field["children"][alternative_name]
+                    if alt_field["type"] == "keyword":
                         # Keyword alternatives return just the alternative name
                         return alternative_name
                     else:
@@ -289,17 +289,17 @@ def __default__(self, data, children, meta):
             # Try with hyphens instead of underscores (reverse of to_rule_name)
             field = self._flat_fields.get(data.replace("_", "-"), None)
         if field is not None:
-            if field.type == "keyword":
+            if field["type"] == "keyword":
                 return data, True
-            elif field.type == "record" and hasattr(field, "children") and field.children:
+            elif field["type"] == "record" and "children" in field and field["children"]:
                 # Transform record fields into dicts with child field names as keys
                 # Keyword children are literals in the grammar and don't appear in children list
                 # Only non-keyword children appear in the children list
                 record_dict = {}
                 non_keyword_children = [
                     (name, child)
-                    for name, child in field.children.items()
-                    if child.type != "keyword"
+                    for name, child in field["children"].items()
+                    if child["type"] != "keyword"
                 ]
                 for i, (child_name, child_field) in enumerate(non_keyword_children):
                     if i < len(children):
@@ -309,7 +309,7 @@ def __default__(self, data, children, meta):
                         else:
                             record_dict[child_name] = children[i]
                 return data, record_dict
-            elif field.type == "union" and hasattr(field, "children") and field.children:
+            elif field["type"] == "union" and "children" in field and field["children"]:
                 # For union fields, return the transformed child
                 # The parser will have selected one alternative
                 return data, children[0] if len(children) == 1 else children
diff --git a/flopy4/mf6/converter/egress/unstructure.py b/flopy4/mf6/converter/egress/unstructure.py
index 3cc7d95e..632f812b 100644
--- a/flopy4/mf6/converter/egress/unstructure.py
+++ b/flopy4/mf6/converter/egress/unstructure.py
@@ -7,14 +7,13 @@
 import numpy as np
 import xarray as xr
 import xattree
-from modflow_devtools.dfns.schema.block import block_sort_key
 from xattree import XatSpec
 
 from flopy4.mf6.binding import Binding
 from flopy4.mf6.component import Component
 from flopy4.mf6.constants import FILL_DNODATA
 from flopy4.mf6.context import Context
-from flopy4.mf6.spec import FileInOut, blocks_dict
+from flopy4.mf6.spec import FileInOut, block_sort_key, blocks_dict
 
 
 def _path_to_tuple(name: str, value: Path, inout: FileInOut) -> tuple[str, ...]:
diff --git a/flopy4/mf6/spec.py b/flopy4/mf6/spec.py
index acd08eef..bdc7509b 100644
--- a/flopy4/mf6/spec.py
+++ b/flopy4/mf6/spec.py
@@ -5,19 +5,13 @@
 
 import builtins
 import types
-import warnings
 from datetime import datetime
 from pathlib import Path
 from typing import Literal, Union, get_args, get_origin
 
 import numpy as np
 from attrs import NOTHING, Attribute
-
-with warnings.catch_warnings():
-    warnings.filterwarnings("ignore", message=".*modflow_devtools.dfns.*experimental.*")
-    from modflow_devtools.dfns.schema.block import block_sort_key
-from modflow_devtools.dfns.schema.v2 import Field as FieldV2
-from modflow_devtools.dfns.schema.v2 import FieldType
+from modflow_devtools.dfn.schema import Field, FieldType
 
 from flopy4.spec import array as flopy_array
 from flopy4.spec import coord as flopy_coord
@@ -352,7 +346,7 @@ def get_field_type(attribute: Attribute) -> FieldType:
     raise ValueError(f"Could not map {attribute.name} to a valid MF6 type.")
 
 
-def to_field(attribute: Attribute) -> FieldV2:
+def to_field(attribute: Attribute) -> Field:
     """
     Convert a `xattree` field specification to a field as defined by the
     MODFLOW 6 input definition language:
@@ -360,7 +354,7 @@ def to_field(attribute: Attribute) -> FieldV2:
     """
     if (xatmeta := attribute.metadata.get("xattree", None)) is None:
         raise ValueError(f"Attribute {attribute.name} in {attribute.name} has no xattree metadata.")
-    return FieldV2(
+    return Field(
         name=attribute.name,
         type=get_field_type(attribute),
         shape=xatmeta.get("dims", None),
@@ -371,3 +365,19 @@ def to_field(attribute: Attribute) -> FieldV2:
         if attribute.metadata.get("kind", None) == "child"  # type: ignore
         else None,  # type: ignore
     )
+
+
+def block_sort_key(item) -> int:
+    # TODO: remove when no longer needed, block order should
+    # be as appears in the definition
+    k, _ = item
+    if k == "options":
+        return 0
+    elif k == "dimensions":
+        return 1
+    elif k == "griddata":
+        return 2
+    elif "period" in k:
+        return 4
+    else:
+        return 3
diff --git a/flopy4/mf6/utils/codegen/filters.py b/flopy4/mf6/utils/codegen/filters.py
index 31272d1a..c973ca15 100644
--- a/flopy4/mf6/utils/codegen/filters.py
+++ b/flopy4/mf6/utils/codegen/filters.py
@@ -1,7 +1,7 @@
 """
 Python-side filters for MF6 code generation.
 
-Converts modflow_devtools.dfns Dfn/Field dataclasses to the context
+Converts modflow_devtools.dfn.Dfn/Field dataclasses to the context
 dicts consumed by Jinja templates. Keeping computation here (rather
 than in Jinja macros) makes edge-case handling easier to test and debug.
 """
@@ -12,8 +12,7 @@
 from dataclasses import dataclass
 from pathlib import Path
 
-from modflow_devtools.dfns import Dfn
-from modflow_devtools.dfns.schema.field import Field
+from modflow_devtools.dfn import Dfn, Field
 
 from .overrides import apply as apply_override
 
@@ -82,7 +81,7 @@ def output_path(dfn_name: str, root: Path) -> Path:
 
 def has_period_block(dfn: Dfn) -> bool:
     """True if the DFN defines a period block (stress package)."""
-    return "period" in (dfn.blocks or {})
+    return "period" in (dfn["blocks"] or {})
 
 
 def has_dimensions_block(dfn: Dfn) -> bool:
@@ -93,7 +92,7 @@ def has_dimensions_block(dfn: Dfn) -> bool:
     Packages like MVR/BUY/VSC have user-specified dimension scalars
     (maxmvr, maxpackages, nrhospecies) that must NOT be init=False.
     """
-    dim_block = (dfn.blocks or {}).get("dimensions", {})
+    dim_block = (dfn.get("blocks", {}) or {}).get("dimensions", {})
     return "maxbound" in dim_block
 
 
@@ -130,26 +129,26 @@ def has_dimensions_block(dfn: Dfn) -> bool:
 
 
 def _has_file_child(f: Field) -> bool:
-    if f.children:
-        return "filein" in f.children or "fileout" in f.children
+    if f.get("children", None):
+        return "filein" in f["children"] or "fileout" in f["children"]
     # v1 DFN fields encode subfields in the type string, e.g.
     # "record ts6 filein ts6_filename" — check there instead.
-    return " filein " in f.type or " fileout " in f.type
+    return " filein " in f["type"] or " fileout " in f["type"]
 
 
 def _has_file_child_of(f: Field, kind: str) -> bool:
     """True if the record has a child of the given kind ('filein' or 'fileout')."""
-    if f.children:
-        return kind in f.children
-    return f" {kind} " in f.type
+    if f.get("children", None):
+        return kind in f["children"]
+    return f" {kind} " in f["type"]
 
 
 def _file_record_subfield_names(f: Field) -> frozenset[str]:
     """Return the subfield names encoded in a v1 DFN record type string."""
-    if f.children:
-        return frozenset(f.children)
+    if f.get("children", None):
+        return frozenset(f["children"])
     # type string format: "record name1 name2 ..."
-    parts = f.type.split()
+    parts = f["type"].split()
     return frozenset(parts[1:]) if len(parts) > 1 else frozenset()
 
 
@@ -162,15 +161,15 @@ def _resolve_alt_grid(shape: str) -> str:
 
 def _has_complex_shape(f: Field) -> bool:
     """True for shapes with unsupported alternative-grid or arithmetic notation."""
-    if not f.shape:
+    if not f.get("shape", None):
         return False
-    resolved = _resolve_alt_grid(f.shape)
+    resolved = _resolve_alt_grid(f["shape"])
     return "*" in resolved or ";" in resolved
 
 
 def is_scalar(f: Field) -> bool:
     """True for simple scalar fields (no shape)."""
-    return f.type in _SCALAR_TYPES and not f.shape
+    return f["type"] in _SCALAR_TYPES and not f.get("shape", None)
 
 
 _STRING_LENGTH_DIMS = frozenset({"lenbigline", "linelength"})
@@ -183,11 +182,15 @@ def is_array(f: Field) -> bool:
     """
     # TODO: emit string fields shaped only by lenbigline/linelength as field(Optional[str]);
     # for now exclude so they fall to scalar handling (see ncf.py Ncf.wkt for the pattern).
-    if f.type == "string" and f.shape and all(s in _STRING_LENGTH_DIMS for s in f.shape):
+    if (
+        f["type"] == "string"
+        and f.get("shape", None)
+        and all(s in _STRING_LENGTH_DIMS for s in f.get("shape", None))
+    ):
         return False
     return (
-        f.type in _ARRAY_BASE_TYPES
-        and bool(f.shape)
+        f["type"] in _ARRAY_BASE_TYPES
+        and bool(f.get("shape", None))
         and not _has_complex_shape(f)
         and not is_aux_list_field(f)
     )
@@ -195,12 +198,12 @@ def is_array(f: Field) -> bool:
 
 def is_keyword_array(f: Field) -> bool:
     """True for boolean-array fields (keyword type with shape)."""
-    return f.type == "keyword" and bool(f.shape) and not _has_complex_shape(f)
+    return f["type"] == "keyword" and bool(f.get("shape", None)) and not _has_complex_shape(f)
 
 
 def is_file_record(f: Field) -> bool:
     """True for record fields whose children include filein or fileout."""
-    return f.type.startswith("record") and _has_file_child(f)
+    return f["type"].startswith("record") and _has_file_child(f)
 
 
 def is_aux_list_field(f: Field) -> bool:
@@ -209,22 +212,27 @@ def is_aux_list_field(f: Field) -> bool:
     These are generated as ``Optional[list[str]]`` with no dims and no
     structure_array converter, matching the hand-written pattern.
     """
-    return f.type == "string" and f.block == "options" and bool(f.shape) and "naux" in f.shape
+    return (
+        f["type"] == "string"
+        and f["block"] == "options"
+        and bool(f.get("shape", None))
+        and "naux" in f.get("shape", None)
+    )
 
 
 def is_period_array(f: Field) -> bool:
     """True for array fields in the period block."""
-    return f.block == "period" and (is_array(f) or is_keyword_array(f))
+    return f["block"] == "period" and (is_array(f) or is_keyword_array(f))
 
 
 def is_dimensions_scalar(f: Field) -> bool:
     """True for scalar fields in the dimensions block (computed, init=False)."""
-    return f.block == "dimensions" and is_scalar(f)
+    return f["block"] == "dimensions" and is_scalar(f)
 
 
 def is_boundname_field(f: Field) -> bool:
     """True for the boundname string array in the period block."""
-    return f.block == "period" and f.name == "boundname"
+    return f["block"] == "period" and f["name"] == "boundname"
 
 
 # Per-package OC record types.  Each entry maps a DFN name to the list of
@@ -245,16 +253,16 @@ def is_oc_record(f: Field, dfn_name: str) -> bool:
     being emitted as inner classes or TODO comments.
     """
     return (
-        f.block == "period"
-        and f.type.startswith("record")
-        and f.name in ("saverecord", "printrecord")
+        f["block"] == "period"
+        and f["type"].startswith("record")
+        and f["name"] in ("saverecord", "printrecord")
         and dfn_name in _OC_RTYPES
     )
 
 
 def is_list_field(f: Field) -> bool:
     """True for list-type sub-table fields (packagedata, perioddata, etc.)."""
-    return f.type == "list"
+    return f["type"] == "list"
 
 
 def list_columns(f: Field) -> list[dict]:
@@ -264,9 +272,9 @@ def list_columns(f: Field) -> list[dict]:
     objects.  The list field has a single record child dict; the column
     entries are that record's ``children`` mapping.
     """
-    if not f.children:
+    if not f.get("children", None):
         return []
-    record_child = next(iter(f.children.values()))
+    record_child = next(iter(f["children"].values()))
     if not isinstance(record_child, dict):
         return []
     return list(record_child.get("children", {}).values())
@@ -281,9 +289,9 @@ def list_col_dim(f: Field, dfn: Dfn) -> str | None:
     Falls back to the single entry in the DFN's dimensions block.
     Returns None when the dimension cannot be determined unambiguously.
     """
-    dim_block = (dfn.blocks or {}).get("dimensions", {})
-    if f.shape:
-        inner = f.shape.strip().strip("()")
+    dim_block = (dfn["blocks"] or {}).get("dimensions", {})
+    if shape := f.get("shape", None):
+        inner = shape.strip().strip("()")
         parts = [p.strip() for p in inner.split(",") if p.strip()]
         if parts:
             shape_dim = _DIM_ALIASES.get(parts[-1], parts[-1])
@@ -343,9 +351,9 @@ def can_generate_record_class(f: Field) -> bool:
     empty inner class.  Records with unsupported child types (recarray, union,
     complex shapes) fall back to TODO comments.
     """
-    if is_file_record(f) or not f.children:
+    if is_file_record(f) or not f.get("children", None):
         return False
-    children = list(f.children.values())
+    children = list(f["children"].values())
     _supported = _RECORD_CLASS_SCALAR_TYPES | {"keyword"}
     all_supported = all(c.get("type") in _supported for c in children)
     if not all_supported:
@@ -366,9 +374,9 @@ def can_expand_record(f: Field) -> bool:
     can't be generated standalone are noted in a TODO comment but don't
     block expansion.
     """
-    if is_file_record(f) or not f.children:
+    if is_file_record(f) or not f.get("children", None):
         return False
-    for child in f.children.values():
+    for child in f["children"].values():
         if not child.get("optional", False) and not _is_expandable_child(child):
             return False
     return True
@@ -383,10 +391,10 @@ def skip_reason(f: Field) -> str | None:
     if can_expand_record(f):
         return None  # handled by _expand_record_field in make.py
     if _has_complex_shape(f):
-        return f"complex shape '{f.shape}' not yet supported"
-    if f.type in ("record", "recarray", "keystring"):
-        return f"complex type '{f.type}' not yet supported"
-    return f"type '{f.type}' not yet supported"
+        return f"complex shape '{f.get('shape', None)}' not yet supported"
+    if f["type"] in ("record", "recarray", "keystring"):
+        return f"complex type '{f['type']}' not yet supported"
+    return f"type '{f['type']}' not yet supported"
 
 
 # Field iteration
@@ -404,18 +412,18 @@ def flat_fields(dfn: Dfn, *, developmode: bool = False) -> list[Field]:
     """
     # Collect subfield names from file records so they can be suppressed.
     subfield_names: set[str] = set()
-    for block in (dfn.blocks or {}).values():
+    for block in (dfn.get("blocks", {}) or {}).values():
         for f in block.values():
             if is_file_record(f):
                 subfield_names.update(_file_record_subfield_names(f))
 
     result = []
-    for block in (dfn.blocks or {}).values():
+    for block in (dfn.get("blocks", {}) or {}).values():
         for f in block.values():
-            f = apply_override(dfn.name, f)
-            if f.developmode and not developmode:
+            f = apply_override(dfn["name"], f)
+            if f.get("developmode", False) and not developmode:
                 continue
-            if f.name in subfield_names:
+            if f["name"] in subfield_names:
                 continue
             result.append(f)
     return result
@@ -451,23 +459,23 @@ def py_type(f: Field) -> str:
     elif is_keyword_array(f):
         base = "NDArray[np.bool_]"
     elif is_array(f):
-        dtype = ARRAY_NUMPY_DTYPES.get(f.type, "np.object_")
+        dtype = ARRAY_NUMPY_DTYPES.get(f["type"], "np.object_")
         base = f"NDArray[{dtype}]"
     elif is_dimensions_scalar(f):
         # dimensions fields are computed (init=False) and always nullable
-        base = _SCALAR_PY_TYPES.get(f.type, "Any")
+        base = _SCALAR_PY_TYPES.get(f["type"], "Any")
         return f"Optional[{base}]"
     elif is_scalar(f):
         # Keywords are always bool (not Optional[bool]) regardless of optional flag.
-        if f.type == "keyword":
+        if f["type"] == "keyword":
             return "bool"
-        base = _SCALAR_PY_TYPES.get(f.type, "Any")
+        base = _SCALAR_PY_TYPES.get(f["type"], "Any")
     else:
         base = "Any"
 
     # Period-block arrays can be absent for a given stress period, so they're
     # implicitly nullable at the Python level even when the DFN marks them required.
-    is_nullable = f.optional or is_period_array(f)
+    is_nullable = f.get("optional", None) or is_period_array(f)
     return f"Optional[{base}]" if is_nullable else base
 
 
@@ -519,15 +527,16 @@ def _longname_repr(longname: str | None) -> str | None:
 
 def _default_repr(f: Field) -> str:
     """Return the Python repr of a field's default value."""
-    if f.default is None:
+    default = f.get("default", None)
+    if default is None:
         # Scalar keywords default to False (absent == not set).
         # Arrays (including keyword arrays) default to None.
-        if f.type == "keyword" and not f.shape:
+        if f["type"] == "keyword" and not f.get("shape", None):
             return "False"
         return "None"
-    if isinstance(f.default, str):
-        return repr(f.default)
-    return repr(f.default)
+    if isinstance(default, str):
+        return repr(default)
+    return repr(default)
 
 
 def _array_args(f: Field, *, has_maxbound: bool = False) -> list[str]:
@@ -538,26 +547,26 @@ def _array_args(f: Field, *, has_maxbound: bool = False) -> list[str]:
     the boundname field; everything else (dims, netcdf, converter,
     on_setattr, longname) is identical.
     """
-    shape = f.shape
+    shape = f.get("shape", None)
     # G/A variant period aux: DFN shape omits naux (one readarray block per aux
     # variable), but the array still needs a trailing naux dimension.
-    if f.name == "aux" and f.block == "period" and shape and "naux" not in shape:
+    if f["name"] == "aux" and f["block"] == "period" and shape and "naux" not in shape:
         shape = shape.rstrip(")").rstrip() + ", naux)"
     _keep = frozenset({"naux"}) if shape and "naux" in shape else None
     dims = _dims_tuple(shape, keep=_keep) if shape else '("nodes",)'
     args = [
-        f'block="{f.block}"',
+        f'block="{f["block"]}"',
         f"dims={dims}",
         f"default={_default_repr(f)}",
     ]
-    if f.netcdf:
+    if f.get("netcdf", False):
         args.append("netcdf=True")
     args.append("converter=Converter(structure_array, takes_self=True, takes_field=True)")
     if is_period_array(f) and has_maxbound:
         args.append("on_setattr=update_maxbound")
     if is_boundname_field(f):
         args.insert(0, f"dtype={_BOUNDNAME_DTYPE}")
-    if ln := _longname_repr(f.longname):
+    if ln := _longname_repr(f.get("longname", None)):
         args.append(f"longname={ln}")
     return args
 
@@ -577,15 +586,17 @@ def spec_call(f: Field, *, has_maxbound: bool = False) -> str:
     can reformat it to the project's style.
     """
     if is_aux_list_field(f):
-        args = [f'block="{f.block}"', f"default={_default_repr(f)}"]
-        if ln := _longname_repr(f.longname):
+        block = f["block"]
+        args = [f'block="{block}"', f"default={_default_repr(f)}"]
+        if ln := _longname_repr(f["longname"]):
             args.append(f"longname={ln}")
         return f"array({', '.join(args)})"
 
     if is_file_record(f):
+        block = f["block"]
         inout = "filein" if _has_file_child_of(f, "filein") else "fileout"
         args = [
-            f'block="{f.block}"',
+            f'block="{block}"',
             f"default={_default_repr(f)}",
             "converter=to_path",
             f'inout="{inout}"',
@@ -597,32 +608,39 @@ def spec_call(f: Field, *, has_maxbound: bool = False) -> str:
 
     # scalar field
     if is_dimensions_scalar(f):
-        if has_maxbound and f.name == "maxbound":
+        block = f["block"]
+        if has_maxbound and f["name"] == "maxbound":
             # Only maxbound itself is auto-computed from data, so init=False.
             # Other dimension scalars in the same block (e.g. nseg in EVT) are
             # user-specified and must remain in __init__.
-            args = [f'block="{f.block}"', f"default={_default_repr(f)}", "init=False"]
-            if f.longname:
-                args.append(f"longname={repr(f.longname)}")
+            args = [f'block="{block}"', f"default={_default_repr(f)}", "init=False"]
+            if f.get("longname", None):
+                args.append(f"longname={repr(f['longname'])}")
             return f"field({', '.join(args)})"
         else:
             # User-specified dims (nseg, nrhospecies, maxmvr, maxpackages, …):
             # use dim(coord=False) so xattree includes the value in its
             # dimension resolution when expanding array fields.
-            args = [f'block="{f.block}"', "coord=False", f"default={_default_repr(f)}"]
-            if f.longname:
-                args.append(f"longname={repr(f.longname)}")
+            block = f["block"]
+            args = [f'block="{block}"', "coord=False", f"default={_default_repr(f)}"]
+            if f.get("longname", None):
+                args.append(f"longname={repr(f['longname'])}")
             return f"dim({', '.join(args)})"
     # Required scalar with no DFN default: omit default= entirely so the field is
     # positional-required at construction.  Matches MF6 semantics (the user MUST
     # supply a value) and avoids the float/int annotation contradicting default=None.
-    if is_scalar(f) and not f.optional and f.default is None and f.type != "keyword":
-        args = [f'block="{f.block}"']
-        if ln := _longname_repr(f.longname):
+    if (
+        is_scalar(f)
+        and not f.get("optional", False)
+        and f.get("default", None) is None
+        and f["type"] != "keyword"
+    ):
+        args = [f'block="{f["block"]}"']
+        if ln := _longname_repr(f.get("longname", None)):
             args.append(f"longname={ln}")
         return f"field({', '.join(args)})"
-    args = [f'block="{f.block}"', f"default={_default_repr(f)}"]
-    if ln := _longname_repr(f.longname):
+    args = [f'block="{f["block"]}"', f"default={_default_repr(f)}"]
+    if ln := _longname_repr(f.get("longname", None)):
         args.append(f"longname={ln}")
     return f"field({', '.join(args)})"
 
@@ -658,7 +676,8 @@ def needed_imports(
     has_aux_list = any(is_aux_list_field(f) for f in generatable_fields)
     has_path = any(is_file_record(f) for f in generatable_fields) or has_injected_paths
     has_optional = any(
-        (f.optional or is_period_array(f)) and f.type != "keyword" for f in generatable_fields
+        (f.get("optional", False) or is_period_array(f)) and f["type"] != "keyword"
+        for f in generatable_fields
     )
     has_dimensions = any(is_dimensions_scalar(f) for f in generatable_fields)
     has_stress_arrays = any(is_period_array(f) for f in generatable_fields)
@@ -699,7 +718,7 @@ def needed_imports(
     }
 
     has_user_dims = (
-        any(is_dimensions_scalar(f) and f.name != "maxbound" for f in generatable_fields)
+        any(is_dimensions_scalar(f) and f["name"] != "maxbound" for f in generatable_fields)
         or has_extra_dims
     )
 
@@ -764,28 +783,30 @@ class ColumnSpec:
 def block_schema(v1_dfn: Dfn, block_name: str) -> list[ColumnSpec]:
     """Derive column schema for a recarray block from a v1 DFN.
 
-    Skips the recarray header field (in_record=False). Returns one
-    ColumnSpec per in_record=True field in DFN order.
+    Finds the list-type header field in the block and reads columns from
+    its nested children (built by the v2.0.0.dev1 migration). Returns one
+    ColumnSpec per column in DFN order.
     """
-    v1_block = (v1_dfn.blocks or {}).get(block_name) or {}
+    v1_block = (v1_dfn["blocks"] or {}).get(block_name) or {}
+    list_field = next((f for f in v1_block.values() if f.get("type") == "list"), None)
+    if list_field is None:
+        return []
     result = []
-    for name, f in v1_block.items():
-        if not getattr(f, "in_record", False):
-            continue
-        ftype = getattr(f, "type", "") or ""
-        optional = _as_bool(getattr(f, "optional", False))
-        tagged = _as_bool(getattr(f, "tagged", False))
-        shape = str(getattr(f, "shape", "") or "")
+    for col in list_columns(list_field):
+        ftype = col.get("type", "") or ""
+        optional_val = col.get("optional")
+        optional = _as_bool(optional_val or False)
+        shape = str(col.get("shape", "") or "")
         is_keyword = ftype.lower() == "keyword"
         result.append(
             ColumnSpec(
-                name=name,
+                name=col.get("name", ""),
                 type=ftype,
-                longname=getattr(f, "longname", "") or "",
+                longname=col.get("longname", "") or "",
                 is_cellid="(ncelldim)" in shape,
-                is_prefix=is_keyword and tagged and not optional,
+                is_prefix=is_keyword and (optional_val is False),
                 is_row_keyword=is_keyword and optional,
-                numeric_index=bool(getattr(f, "numeric_index", False)),
+                numeric_index=bool(col.get("numeric_index", False)),
             )
         )
     return result
@@ -796,9 +817,9 @@ def list_block_names(dfn: Dfn) -> list[str]:
     seen: set[str] = set()
     result = []
     for f in flat_fields(dfn):
-        if is_list_field(f) and f.block not in seen:
-            seen.add(f.block)
-            result.append(f.block)
+        if is_list_field(f) and f["block"] not in seen:
+            seen.add(f["block"])
+            result.append(f["block"])
     return result
 
 
@@ -806,18 +827,18 @@ def v1_list_block_names(v1_dfn: Dfn) -> list[str]:
     """Return recarray block names from a v1 DFN, in order.
 
     A block is a recarray when it contains a header field whose ``type``
-    starts with ``"recarray"``.  This is more precise than checking
-    ``in_record=True``, which also matches sub-fields of compound records
-    (filerecord entries) inside scalar options blocks.
+    is ``"list"`` (v2.0.0.dev1) or starts with ``"recarray"`` (v1).
     Used to discover blocks that dfn2toml dropped from the v2 TOML.
     """
     seen: set[str] = set()
     result = []
-    for block_name, block in (v1_dfn.blocks or {}).items():
+    for block_name, block in (v1_dfn["blocks"] or {}).items():
         if block_name in seen:
             continue
         if any(
-            str(getattr(f, "type", "") or "").lower().startswith("recarray") for f in block.values()
+            (f.get("type", "") or "").lower() == "list"
+            or (f.get("type", "") or "").lower().startswith("recarray")
+            for f in block.values()
         ):
             result.append(block_name)
             seen.add(block_name)
diff --git a/flopy4/mf6/utils/codegen/generate_classes.py b/flopy4/mf6/utils/codegen/generate_classes.py
index a85bf08f..4838071c 100644
--- a/flopy4/mf6/utils/codegen/generate_classes.py
+++ b/flopy4/mf6/utils/codegen/generate_classes.py
@@ -15,7 +15,7 @@
 from pathlib import Path
 
 from modflow_devtools.dfn import get_dfns
-from modflow_devtools.dfns.dfn2toml import convert as dfn2toml
+from modflow_devtools.dfn2toml import convert as dfn2toml
 
 from .make import make_all
 
diff --git a/flopy4/mf6/utils/codegen/make.py b/flopy4/mf6/utils/codegen/make.py
index e895ccc5..a779ac5b 100644
--- a/flopy4/mf6/utils/codegen/make.py
+++ b/flopy4/mf6/utils/codegen/make.py
@@ -14,8 +14,7 @@
 from pathlib import Path
 
 import jinja2
-from modflow_devtools.dfns import Dfn, load_flat
-from modflow_devtools.dfns.schema.field import Field as DfnField
+from modflow_devtools.dfn import Dfn, Field
 
 from . import filters
 from .filters import ColumnSpec
@@ -109,18 +108,18 @@ class ComponentSpec:
 # Context builders
 
 
-def _build_field_spec(f: DfnField, *, has_maxbound: bool = False) -> FieldSpec:
+def _build_field_spec(f: Field, *, has_maxbound: bool = False) -> FieldSpec:
     generatable = filters.is_generatable(f)
     # Strip 'record' suffix from file record names for a cleaner API
     # (e.g. head_filerecord → head_file, budget_filerecord → budget_file).
     # Compound records get the same treatment via _strip_record_words in
     # build_component_spec; this keeps the two paths consistent.
     if filters.is_file_record(f):
-        py_name = filters.safe_name("_".join(_strip_record_words(f.name)))
+        py_name = filters.safe_name("_".join(_strip_record_words(f["name"])))
     else:
-        py_name = filters.safe_name(f.name)
+        py_name = filters.safe_name(f["name"])
     return FieldSpec(
-        dfn_name=f.name,
+        dfn_name=f["name"],
         py_name=py_name,
         type_annotation=filters.py_type(f) if generatable else "Any",
         spec_call=filters.spec_call(f, has_maxbound=has_maxbound) if generatable else "",
@@ -148,14 +147,14 @@ def _build_field_spec(f: DfnField, *, has_maxbound: bool = False) -> FieldSpec:
 )
 
 
-def _child_to_field(child_dict: dict) -> DfnField:
+def _child_to_field(child_dict: dict) -> Field:
     """Convert a record child dict to a Field object."""
-    return DfnField(**{k: v for k, v in child_dict.items() if k in _FIELD_KNOWN_KEYS})
+    return Field(**{k: v for k, v in child_dict.items() if k in _FIELD_KNOWN_KEYS})
 
 
 def _expand_record_field(
-    f: DfnField, *, has_maxbound: bool = False
-) -> tuple[list[FieldSpec], list[DfnField]]:
+    f: Field, *, has_maxbound: bool = False
+) -> tuple[list[FieldSpec], list[Field]]:
     """Expand a compound record into FieldSpecs for its generatable children.
 
     Returns (field_specs, generatable_child_fields).  field_specs contains one
@@ -163,8 +162,8 @@ def _expand_record_field(
     children that can't be generated standalone.  generatable_child_fields is
     the corresponding list of Field objects used for import computation.
     """
-    children = f.children or {}
-    expandable: list[DfnField] = []
+    children = f.get("children", None) or {}
+    expandable: list[Field] = []
     unexpandable_optional: list[str] = []
 
     for child_dict in children.values():
@@ -175,7 +174,7 @@ def _expand_record_field(
         # required unexpandable children were already blocked by can_expand_record
 
     specs: list[FieldSpec] = []
-    gen_fields: list[DfnField] = []
+    gen_fields: list[Field] = []
     for child_field in expandable:
         spec = _build_field_spec(child_field, has_maxbound=has_maxbound)
         specs.append(spec)
@@ -185,8 +184,8 @@ def _expand_record_field(
     if unexpandable_optional:
         specs.append(
             FieldSpec(
-                dfn_name=f.name,
-                py_name=filters.safe_name(f.name),
+                dfn_name=f["name"],
+                py_name=filters.safe_name(f["name"]),
                 type_annotation="Any",
                 spec_call="",
                 generatable=False,
@@ -199,7 +198,7 @@ def _expand_record_field(
     return specs, gen_fields
 
 
-def _expand_list_field(f: DfnField, dfn: Dfn) -> list[FieldSpec]:
+def _expand_list_field(f: Field, dfn: Dfn) -> list[FieldSpec]:
     """Expand a list-type sub-table field into one FieldSpec per column.
 
     Each column becomes an array() field with the list block's block name
@@ -211,8 +210,8 @@ def _expand_list_field(f: DfnField, dfn: Dfn) -> list[FieldSpec]:
     if not cols or dim is None:
         return [
             FieldSpec(
-                dfn_name=f.name,
-                py_name=filters.safe_name(f.name),
+                dfn_name=f["name"],
+                py_name=filters.safe_name(f["name"]),
                 type_annotation="Any",
                 spec_call="",
                 generatable=False,
@@ -222,15 +221,16 @@ def _expand_list_field(f: DfnField, dfn: Dfn) -> list[FieldSpec]:
 
     specs = []
     for col in cols:
-        col = apply_to_child(dfn.name, col)
+        col = apply_to_child(dfn["name"], col)
         col_name = col["name"]
         col_type = col.get("type", "string")
         col_longname = col.get("longname", "")
         dtype = filters.ARRAY_NUMPY_DTYPES.get(col_type, "np.object_")
         base = f"NDArray[{dtype}]"
         annotation = f"Optional[{base}]"  # expanded columns always default to None
+        block = f["block"]
         args = [
-            f'block="{f.block}"',
+            f'block="{block}"',
             f'dims=("{dim}",)',
             "default=None",
             "converter=Converter(structure_array, takes_self=True, takes_field=True)",
@@ -249,7 +249,7 @@ def _expand_list_field(f: DfnField, dfn: Dfn) -> list[FieldSpec]:
     return specs
 
 
-def _expand_oc_record_field(f: DfnField, dfn_name: str) -> list[FieldSpec]:
+def _expand_oc_record_field(f: Field, dfn_name: str) -> list[FieldSpec]:
     """Expand saverecord/printrecord into per-rtype NDArray[np.str_] fields.
 
     Generates one array field per rtype (e.g. save_concentration, save_budget)
@@ -257,7 +257,7 @@ def _expand_oc_record_field(f: DfnField, dfn_name: str) -> list[FieldSpec]:
     by splitting on ``_`` → replacing with space.
     """
     rtypes = filters._OC_RTYPES.get(dfn_name, [])
-    action = "save" if f.name == "saverecord" else "print"
+    action = "save" if f["name"] == "saverecord" else "print"
     specs: list[FieldSpec] = []
     for rtype in rtypes:
         py_name = f"{action}_{rtype}"
@@ -271,7 +271,7 @@ def _expand_oc_record_field(f: DfnField, dfn_name: str) -> list[FieldSpec]:
         )
         specs.append(
             FieldSpec(
-                dfn_name=f"{f.name}_{rtype}",
+                dfn_name=f"{f['name']}_{rtype}",
                 py_name=py_name,
                 type_annotation="Optional[NDArray[np.str_]]",
                 spec_call=spec_call,
@@ -308,7 +308,7 @@ def _strip_record_words(name: str) -> list[str]:
 }
 
 
-def _build_inner_class_spec(f: DfnField, dfn_name: str) -> InnerClassSpec:
+def _build_inner_class_spec(f: Field, dfn_name: str) -> InnerClassSpec:
     """Build an InnerClassSpec for a mixed-type compound record field.
 
     When the first child is a keyword type it becomes the trigger token
@@ -324,7 +324,7 @@ def _build_inner_class_spec(f: DfnField, dfn_name: str) -> InnerClassSpec:
     sub-records lost in v2 TOML conversion) are appended after the direct
     children.  All fields are sorted required-first to satisfy attrs.
     """
-    children = list((f.children or {}).values())
+    children = list((f.get("children", None) or {}).values())
     first = children[0]
     if first.get("type") == "keyword":
         keyword = first["name"]
@@ -372,13 +372,13 @@ def _process_child(child_dict: dict) -> None:
     for child_dict in data_children:
         _process_child(child_dict)
 
-    for child_dict in extra_record_children(dfn_name, f.name):
+    for child_dict in extra_record_children(dfn_name, f["name"]):
         _process_child(child_dict)
 
     # attrs requires fields with defaults to follow fields without defaults.
-    inner_fields.sort(key=lambda field: field.optional)
+    inner_fields.sort(key=lambda field: str(field.optional))
 
-    words = _strip_record_words(f.name)
+    words = _strip_record_words(f["name"])
     class_name = "".join(w.capitalize() for w in words)
     extra_tokens_repr = (
         "(" + ", ".join(f'"{t}"' for t in extra_tokens) + ",)" if extra_tokens else ""
@@ -405,17 +405,17 @@ def _build_block_property_specs(
     block property API for each recarray block.  Returns (specs, block_names)
     where block_names is used as a skip-set in the main field loop.
     """
-    dfn_dims = set((dfn.blocks or {}).get("dimensions", {}).keys())
-    dfn_dims_ordered = list((dfn.blocks or {}).get("dimensions", {}).keys())
+    dfn_dims = set((dfn["blocks"] or {}).get("dimensions", {}).keys())
+    dfn_dims_ordered = list((dfn["blocks"] or {}).get("dimensions", {}).keys())
 
     # Collect v2 list blocks, excluding those handled by TOML overrides.
-    list_fields_map: dict[str, DfnField | None] = {
-        f.block: f
+    list_fields_map: dict[str, Field | None] = {
+        f["block"]: f
         for f in filters.flat_fields(dfn)
         if filters.is_list_field(f)
-        and f.block not in extra_blocks
-        and f.block not in replace_blocks
-        and "period" not in f.block
+        and f["block"] not in extra_blocks
+        and f["block"] not in replace_blocks
+        and "period" not in f["block"]
     }
     # Add recarray blocks present in v1 DFN but dropped by dfn2toml (e.g. SSM sources/fileinput).
     for v1_block in filters.v1_list_block_names(v1_dfn):
@@ -426,7 +426,7 @@ def _build_block_property_specs(
     v1_schemas = {block: filters.block_schema(v1_dfn, block) for block in list_fields_map}
     # Period field bare names: static columns sharing a name with a period field
     # must take the block-prefixed attr name so the period field keeps the bare name.
-    bare_period_names = frozenset(pf["keyword"].lower() for pf in extra_period_fields(dfn.name))
+    bare_period_names = frozenset(pf["keyword"].lower() for pf in extra_period_fields(dfn["name"]))
     collisions = filters.collision_names(v1_schemas, reserved=bare_period_names)
 
     # Resolve which DFN dimension scalar each block maps to.
@@ -442,10 +442,10 @@ def _build_block_property_specs(
         if dfn_dim and dfn_dim in dfn_dims:
             dim_resolutions[block_name] = (dfn_dim, True)
             claimed_dims.add(dfn_dim)
-        elif lf.shape and "maxbound" in str(lf.shape) and dfn_dims:
+        elif lf.get("shape", None) and "maxbound" in str(lf.get("shape", None)) and dfn_dims:
             maxbound_blocks.append(block_name)
         else:
-            override = block_dim_override(dfn.name, block_name)
+            override = block_dim_override(dfn["name"], block_name)
             dim_resolutions[block_name] = (override or f"n{block_name}", False)
 
     unclaimed = [d for d in dfn_dims_ordered if d not in claimed_dims]
@@ -486,15 +486,15 @@ def _build_block_property_specs(
 
 def _base_class(dfn: Dfn) -> str:
     """Determine the Python base class for a component."""
-    if dfn.name.split("-")[0] == _SLN_PREFIX:
+    if dfn["name"].split("-")[0] == _SLN_PREFIX:
         return "Solution"
     return "Package"
 
 
 def _slntype(dfn: Dfn) -> str | None:
     """Return the slntype string for solution DFNs, or None."""
-    if dfn.name.split("-")[0] == _SLN_PREFIX:
-        return dfn.name.split("-")[1]
+    if dfn["name"].split("-")[0] == _SLN_PREFIX:
+        return dfn["name"].split("-")[1]
     return None
 
 
@@ -529,9 +529,9 @@ def build_component_spec(
     period_specs: list[FieldSpec] = []
 
     inner_class_specs: list[InnerClassSpec] = []
-    generatable_field_objects: list[DfnField] = []
-    _replace_blocks = replace_list_blocks(dfn.name)
-    _extra_blocks = {lb["block"] for lb in extra_list_blocks(dfn.name)}
+    generatable_field_objects: list[Field] = []
+    _replace_blocks = replace_list_blocks(dfn["name"])
+    _extra_blocks = {lb["block"] for lb in extra_list_blocks(dfn["name"])}
 
     # BlockPropertySpec for static list blocks — must precede the main field loop
     # since _bp_block_names is used there as a skip-set.
@@ -548,16 +548,16 @@ def build_component_spec(
     has_list_cols = False
     has_oc_fields = False
     for f in all_fields:
-        if filters.is_list_field(f) and f.block in (_replace_blocks | _extra_blocks):
+        if filters.is_list_field(f) and f["block"] in (_replace_blocks | _extra_blocks):
             # List field replaced by explicit path fields or injected via extra_list_blocks.
             continue
-        if filters.is_list_field(f) and f.block in _bp_block_names:
+        if filters.is_list_field(f) and f["block"] in _bp_block_names:
             # List field covered by BlockPropertySpec; column attrs generated below.
             continue
 
-        if f.block in ("options", "dimensions"):
+        if f["block"] in ("options", "dimensions"):
             target = prefix_specs
-        elif "period" in f.block:
+        elif "period" in f["block"]:
             target = period_specs
         else:
             target = data_specs
@@ -566,20 +566,21 @@ def build_component_spec(
             expanded = _expand_list_field(f, dfn)
             target.extend(expanded)
             has_list_cols = has_list_cols or any(fs.generatable for fs in expanded)
-        elif filters.is_oc_record(f, dfn.name):
-            expanded = _expand_oc_record_field(f, dfn.name)
+        elif filters.is_oc_record(f, dfn["name"]):
+            expanded = _expand_oc_record_field(f, dfn["name"])
             target.extend(expanded)
             has_oc_fields = has_oc_fields or any(fs.generatable for fs in expanded)
         elif filters.can_generate_record_class(f):
-            record_spec = _build_inner_class_spec(f, dfn.name)
+            record_spec = _build_inner_class_spec(f, dfn["name"])
             inner_class_specs.append(record_spec)
-            clean_name = filters.safe_name("_".join(_strip_record_words(f.name)))
+            clean_name = filters.safe_name("_".join(_strip_record_words(f["name"])))
+            block = f["block"]
             target.append(
                 FieldSpec(
-                    dfn_name=f.name,
+                    dfn_name=f["name"],
                     py_name=clean_name,
                     type_annotation=f"Optional[{record_spec.class_name}]",
-                    spec_call=f'field(block="{f.block}", default=None)',
+                    spec_call=f'field(block="{block}", default=None)',
                     generatable=True,
                 )
             )
@@ -597,7 +598,7 @@ def build_component_spec(
     # Inject path fields that replace heterogeneous list blocks (e.g. prt-fmi packagedata).
     # Each injected entry becomes an Optional[Path] field using the path() spec.
     has_injected_paths = False
-    for entry in replace_list_fields(dfn.name):
+    for entry in replace_list_fields(dfn["name"]):
         has_injected_paths = True
         ln = entry.get("longname", "")
         args = [
@@ -625,8 +626,8 @@ def build_component_spec(
     # Entries must be listed in dfn_overrides.toml in v1 DFN block order so that
     # stable sort on key 3 in block_sort_key produces the correct write sequence.
     has_extra_dims = False
-    _dfn_dim_names = set((dfn.blocks or {}).get("dimensions", {}).keys())
-    for lb in extra_list_blocks(dfn.name):
+    _dfn_dim_names = set((dfn.get("blocks", {}) or {}).get("dimensions", {}).keys())
+    for lb in extra_list_blocks(dfn["name"]):
         block_name = lb["block"]
         dim_name = lb["dim"]
         # Only add the dim field when it is not already declared in the DFN's
@@ -642,7 +643,7 @@ def build_component_spec(
                     generatable=True,
                 )
             )
-        v1_block = (v1_dfn.blocks or {}).get(block_name, {}) if v1_dfn else {}
+        v1_block = (v1_dfn.get("blocks", {}) or {}).get(block_name, {}) if v1_dfn else {}
         for col in lb.get("columns", []):
             col_name = col["name"]
             col_py_name = filters.safe_name(col.get("py_name", col_name))
@@ -688,7 +689,7 @@ def build_component_spec(
     # Period fields always use the bare keyword name. Static block columns that
     # share a name with a period field take the block-prefixed attr name instead
     # (see _bare_period_names + collision_names(reserved=...)).
-    for pf in extra_period_fields(dfn.name):
+    for pf in extra_period_fields(dfn["name"]):
         kw = pf["keyword"]
         feat_dim = pf["feature_dim"]
         py_name = filters.safe_name(kw.lower())
@@ -813,10 +814,10 @@ def build_component_spec(
     if not _naux_emitted:
         for _f in all_fields:
             if (
-                _f.block == "period"
+                _f["block"] == "period"
                 and filters.is_array(_f)
-                and _f.shape
-                and ("naux" in _f.shape or _f.name == "aux")
+                and _f.get("shape", None)
+                and ("naux" in _f.get("shape", None) or _f["name"] == "aux")
             ):
                 _naux_emitted = True
                 has_extra_dims = True
@@ -841,19 +842,21 @@ def build_component_spec(
     for _f in all_fields:
         # Only node-based floating/integer list columns: excludes keyword period arrays
         # (STO steady-state/transient flags) and non-list period blocks.
-        if not (_f.block == "period" and filters.is_array(_f)):
+        if not (_f["block"] == "period" and filters.is_array(_f)):
             continue
-        if _f.name in ("boundname", "aux"):
+        if _f["name"] in ("boundname", "aux"):
             continue
-        if _f.shape and "naux" in _f.shape:
+        if _f.get("shape", None) and "naux" in _f.get("shape", None):
             continue
         # Require node dimension (nnodes/nodes in shape) — excludes OC and period-level scalars
-        if not _f.shape or ("nnodes" not in _f.shape and "nodes" not in _f.shape):
+        if not _f.get("shape", None) or (
+            "nnodes" not in _f.get("shape", None) and "nodes" not in _f.get("shape", None)
+        ):
             continue
-        period_col_map[_f.name] = filters.safe_name(_f.name)
+        period_col_map[_f["name"]] = filters.safe_name(_f["name"])
 
     base = _base_class(dfn)
-    multi = bool(dfn.multi)
+    multi = bool(dfn.get("multi", False))
     slntype = _slntype(dfn)
     has_inner_classes = bool(inner_class_specs)
 
@@ -874,15 +877,15 @@ def build_component_spec(
     )
 
     return ComponentSpec(
-        dfn_name=dfn.name,
-        class_name=filters.class_name(dfn.name),
+        dfn_name=dfn["name"],
+        class_name=filters.class_name(dfn["name"]),
         base_class=base,
         multi=multi,
         slntype=slntype,
         imports=imports,
         fields=field_specs,
         inner_classes=inner_class_specs,
-        outpath=filters.output_path(dfn.name, root),
+        outpath=filters.output_path(dfn["name"], root),
         block_properties=block_properties,
         has_aux=_naux_emitted,
         period_col_map=period_col_map,
@@ -982,8 +985,8 @@ def make_all(
     outdir = Path(outdir)
     skip = skip or set()
     env = _get_env()
-    dfns = load_flat(dfndir)
-    v1_dfns = load_flat(v1dfndir) if v1dfndir else {}
+    dfns = Dfn.load_all(dfndir, schema_version="2.0.0.dev1")
+    v1_dfns = Dfn.load_all(v1dfndir, schema_version="2.0.0.dev1") if v1dfndir else {}
     specs = []
     for name, dfn in dfns.items():
         if name in skip:
diff --git a/flopy4/mf6/utils/codegen/overrides.py b/flopy4/mf6/utils/codegen/overrides.py
index 64a627c8..01d232fd 100644
--- a/flopy4/mf6/utils/codegen/overrides.py
+++ b/flopy4/mf6/utils/codegen/overrides.py
@@ -18,11 +18,10 @@
     patched_field = apply("gwf-ic", field)
 """
 
-import dataclasses
 import tomllib
 from pathlib import Path
 
-from modflow_devtools.dfns.schema.field import Field
+from modflow_devtools.dfn import Field
 
 _OVERRIDES_PATH = Path(__file__).parent / "dfn_overrides.toml"
 
@@ -53,12 +52,12 @@ def apply(dfn_name: str, f: Field) -> Field:
         The original field if no overrides exist, otherwise a new
         dataclass instance with the patched attributes.
     """
-    patches = _OVERRIDES.get(dfn_name, {}).get(f.name, {})
+    patches = _OVERRIDES.get(dfn_name, {}).get(f["name"], {})
     # extra_children is consumed by extra_record_children(), not a Field attribute
     patches = {k: v for k, v in patches.items() if k != "extra_children"}
     if not patches:
         return f
-    return dataclasses.replace(f, **patches)
+    return {**f, **patches}
 
 
 def extra_list_blocks(dfn_name: str) -> list[dict]:
diff --git a/pixi.lock b/pixi.lock
index 71c6c108..874744dc 100644
--- a/pixi.lock
+++ b/pixi.lock
@@ -88,7 +88,7 @@ environments:
       - conda: https://conda.anaconda.org/conda-forge/noarch/python_abi-3.13-8_cp313.conda
       - conda: https://conda.anaconda.org/conda-forge/noarch/tzdata-2025c-hc9c84f9_1.conda
       - pypi: .
-      - pypi: git+https://github.com/modflow-org/modflow-devtools#06e14c20c250bada77b3facb57fa3a286c4c211d
+      - pypi: git+https://github.com/modflow-org/modflow-devtools#5fde75e2b737b698795c30d993340f956350dbda
       - pypi: git+https://github.com/wpbonelli/xattree#82942ffb8237d56c97451765ac3e2b16d6cb0d2c
       - pypi: https://files.pythonhosted.org/packages/02/be/5d2d47b1fb58943194fb59dcf222f7c4e35122ec0ffe8c36e18b5d728f0b/tblib-3.2.2-py3-none-any.whl
       - pypi: https://files.pythonhosted.org/packages/07/f8/41db9de19d7987d6b04715a02b3b40aea467000275d9d758ffaa31af7d50/pydantic_core-2.46.4-cp313-cp313-manylinux_2_17_x86_64.manylinux2014_x86_64.whl
@@ -113,6 +113,7 @@ environments:
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       - pypi: https://files.pythonhosted.org/packages/52/07/1922a0c20ed4c95769937619d2c0217ee3f665a8b967438277d3f40860e4/xugrid-0.14.3-py3-none-any.whl
       - pypi: https://files.pythonhosted.org/packages/5d/ba/459f18c16f2b3fc1a1ca871f72f07d70c07bf768ad0a507a698b8052ac58/msgpack-1.1.2-cp313-cp313-manylinux2014_x86_64.manylinux_2_17_x86_64.manylinux_2_28_x86_64.whl
+      - pypi: https://files.pythonhosted.org/packages/5d/f3/1f8651f23101e6fae41d0d504414c9722b0140bf0fc6acf87ac52e18aa41/pyaml-26.2.1-py3-none-any.whl
       - pypi: https://files.pythonhosted.org/packages/5e/f5/0c41cb68dcae6b7de4fac4188a3a9589e21fb31df21ea3a2e888db95e6c9/soupsieve-2.8.4-py3-none-any.whl
       - pypi: https://files.pythonhosted.org/packages/62/a1/3d680cbfd5f4b8f15abc1d571870c5fc3e594bb582bc3b64ea099db13e56/jinja2-3.1.6-py3-none-any.whl
       - pypi: https://files.pythonhosted.org/packages/67/ee/21d4e8536afd1a328f01b359b4d3997b291ffd35a237c877b331c1c3b71c/pillow-12.2.0-cp313-cp313-manylinux_2_27_x86_64.manylinux_2_28_x86_64.whl
@@ -228,7 +229,7 @@ environments:
       - conda: https://conda.anaconda.org/conda-forge/osx-64/tk-8.6.13-h7142dee_3.conda
       - conda: https://conda.anaconda.org/conda-forge/osx-64/zstd-1.5.7-h3eecb57_6.conda
       - pypi: .
-      - pypi: git+https://github.com/modflow-org/modflow-devtools#06e14c20c250bada77b3facb57fa3a286c4c211d
+      - pypi: git+https://github.com/modflow-org/modflow-devtools#5fde75e2b737b698795c30d993340f956350dbda
       - pypi: git+https://github.com/wpbonelli/xattree#82942ffb8237d56c97451765ac3e2b16d6cb0d2c
       - pypi: https://files.pythonhosted.org/packages/01/88/a8952b6d5c21e74cbf158515b779666f692846502623e9e3c39d8e8ba25f/llvmlite-0.47.0.tar.gz
       - pypi: https://files.pythonhosted.org/packages/02/be/5d2d47b1fb58943194fb59dcf222f7c4e35122ec0ffe8c36e18b5d728f0b/tblib-3.2.2-py3-none-any.whl
@@ -254,6 +255,7 @@ environments:
       - pypi: https://files.pythonhosted.org/packages/50/bd/c336448be43d40be28e71f2e0f3caf7ccb28e2755c58f4c02c065bfe3e8e/WebOb-1.8.9-py2.py3-none-any.whl
       - pypi: https://files.pythonhosted.org/packages/51/a2/5d30b469c5267a17b39dec53208222f76a8d351dfac4af661888c5aee77d/pydantic_core-2.46.4-cp313-cp313-macosx_10_12_x86_64.whl
       - pypi: https://files.pythonhosted.org/packages/52/07/1922a0c20ed4c95769937619d2c0217ee3f665a8b967438277d3f40860e4/xugrid-0.14.3-py3-none-any.whl
+      - pypi: https://files.pythonhosted.org/packages/5d/f3/1f8651f23101e6fae41d0d504414c9722b0140bf0fc6acf87ac52e18aa41/pyaml-26.2.1-py3-none-any.whl
       - pypi: https://files.pythonhosted.org/packages/5e/f5/0c41cb68dcae6b7de4fac4188a3a9589e21fb31df21ea3a2e888db95e6c9/soupsieve-2.8.4-py3-none-any.whl
       - pypi: https://files.pythonhosted.org/packages/62/a1/3d680cbfd5f4b8f15abc1d571870c5fc3e594bb582bc3b64ea099db13e56/jinja2-3.1.6-py3-none-any.whl
       - pypi: https://files.pythonhosted.org/packages/68/35/0167aad910bbdb9599272bd96d01a9ec6852f36b9455cf2ca67bd4cc2d23/contourpy-1.3.3-cp313-cp313-macosx_10_13_x86_64.whl
@@ -376,7 +378,7 @@ environments:
       - conda: https://conda.anaconda.org/conda-forge/osx-arm64/tk-8.6.13-h010d191_3.conda
       - conda: https://conda.anaconda.org/conda-forge/osx-arm64/zstd-1.5.7-hbf9d68e_6.conda
       - pypi: .
-      - pypi: git+https://github.com/modflow-org/modflow-devtools#06e14c20c250bada77b3facb57fa3a286c4c211d
+      - pypi: git+https://github.com/modflow-org/modflow-devtools#5fde75e2b737b698795c30d993340f956350dbda
       - pypi: git+https://github.com/wpbonelli/xattree#82942ffb8237d56c97451765ac3e2b16d6cb0d2c
       - pypi: https://files.pythonhosted.org/packages/02/be/5d2d47b1fb58943194fb59dcf222f7c4e35122ec0ffe8c36e18b5d728f0b/tblib-3.2.2-py3-none-any.whl
       - pypi: https://files.pythonhosted.org/packages/04/90/67bd7260b4ea9b8b20b4f58afef6c223ecb3abf368eb4ec5bc2cdef81b49/pyproj-3.7.2.tar.gz
@@ -399,6 +401,7 @@ environments:
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       - pypi: https://files.pythonhosted.org/packages/52/07/1922a0c20ed4c95769937619d2c0217ee3f665a8b967438277d3f40860e4/xugrid-0.14.3-py3-none-any.whl
       - pypi: https://files.pythonhosted.org/packages/59/8c/77f5097695f4dd8255ecbd08b2a1ed8ba8b953d337804dd7080f199e12bf/tornado-6.5.5-cp39-abi3-macosx_10_9_universal2.whl
+      - pypi: https://files.pythonhosted.org/packages/5d/f3/1f8651f23101e6fae41d0d504414c9722b0140bf0fc6acf87ac52e18aa41/pyaml-26.2.1-py3-none-any.whl
       - pypi: https://files.pythonhosted.org/packages/5e/f5/0c41cb68dcae6b7de4fac4188a3a9589e21fb31df21ea3a2e888db95e6c9/soupsieve-2.8.4-py3-none-any.whl
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@@ -520,7 +523,7 @@ environments:
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       - conda: https://conda.anaconda.org/conda-forge/win-64/zstd-1.5.7-h534d264_6.conda
       - pypi: .
-      - pypi: git+https://github.com/modflow-org/modflow-devtools#06e14c20c250bada77b3facb57fa3a286c4c211d
+      - pypi: git+https://github.com/modflow-org/modflow-devtools#5fde75e2b737b698795c30d993340f956350dbda
       - pypi: git+https://github.com/wpbonelli/xattree#82942ffb8237d56c97451765ac3e2b16d6cb0d2c
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+      - pypi: https://files.pythonhosted.org/packages/5d/f3/1f8651f23101e6fae41d0d504414c9722b0140bf0fc6acf87ac52e18aa41/pyaml-26.2.1-py3-none-any.whl
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@@ -683,7 +687,7 @@ environments:
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       - conda: https://conda.anaconda.org/conda-forge/noarch/tzdata-2025c-hc9c84f9_1.conda
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       - conda: https://conda.anaconda.org/conda-forge/noarch/tzdata-2025c-hc9c84f9_1.conda
       - pypi: .
-      - pypi: git+https://github.com/modflow-org/modflow-devtools#06e14c20c250bada77b3facb57fa3a286c4c211d
+      - pypi: git+https://github.com/modflow-org/modflow-devtools#5fde75e2b737b698795c30d993340f956350dbda
       - pypi: git+https://github.com/wpbonelli/xattree#82942ffb8237d56c97451765ac3e2b16d6cb0d2c
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+      - pypi: https://files.pythonhosted.org/packages/5d/f3/1f8651f23101e6fae41d0d504414c9722b0140bf0fc6acf87ac52e18aa41/pyaml-26.2.1-py3-none-any.whl
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@@ -5040,7 +5061,7 @@ environments:
       - conda: https://conda.anaconda.org/conda-forge/osx-64/tk-8.6.13-h7142dee_3.conda
       - conda: https://conda.anaconda.org/conda-forge/osx-64/zstd-1.5.7-h3eecb57_6.conda
       - pypi: .
-      - pypi: git+https://github.com/modflow-org/modflow-devtools#06e14c20c250bada77b3facb57fa3a286c4c211d
+      - pypi: git+https://github.com/modflow-org/modflow-devtools#5fde75e2b737b698795c30d993340f956350dbda
       - pypi: git+https://github.com/wpbonelli/xattree#82942ffb8237d56c97451765ac3e2b16d6cb0d2c
       - pypi: https://files.pythonhosted.org/packages/01/88/a8952b6d5c21e74cbf158515b779666f692846502623e9e3c39d8e8ba25f/llvmlite-0.47.0.tar.gz
       - pypi: https://files.pythonhosted.org/packages/02/be/5d2d47b1fb58943194fb59dcf222f7c4e35122ec0ffe8c36e18b5d728f0b/tblib-3.2.2-py3-none-any.whl
@@ -5093,6 +5114,7 @@ environments:
       - pypi: https://files.pythonhosted.org/packages/52/07/1922a0c20ed4c95769937619d2c0217ee3f665a8b967438277d3f40860e4/xugrid-0.14.3-py3-none-any.whl
       - pypi: https://files.pythonhosted.org/packages/54/20/4d324d65cc6d9205fabedc306948156824eb9f0ee1633355a8f7ec5c66bf/pluggy-1.6.0-py3-none-any.whl
       - pypi: https://files.pythonhosted.org/packages/56/6d/0d9848617b9f753b87f214f1c682592f7ca42de085f564352f10f0843026/ipywidgets-8.1.8-py3-none-any.whl
+      - pypi: https://files.pythonhosted.org/packages/5d/f3/1f8651f23101e6fae41d0d504414c9722b0140bf0fc6acf87ac52e18aa41/pyaml-26.2.1-py3-none-any.whl
       - pypi: https://files.pythonhosted.org/packages/5e/f5/0c41cb68dcae6b7de4fac4188a3a9589e21fb31df21ea3a2e888db95e6c9/soupsieve-2.8.4-py3-none-any.whl
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@@ -5284,7 +5306,7 @@ environments:
       - conda: https://conda.anaconda.org/conda-forge/osx-arm64/tk-8.6.13-h010d191_3.conda
       - conda: https://conda.anaconda.org/conda-forge/osx-arm64/zstd-1.5.7-hbf9d68e_6.conda
       - pypi: .
-      - pypi: git+https://github.com/modflow-org/modflow-devtools#06e14c20c250bada77b3facb57fa3a286c4c211d
+      - pypi: git+https://github.com/modflow-org/modflow-devtools#5fde75e2b737b698795c30d993340f956350dbda
       - pypi: git+https://github.com/wpbonelli/xattree#82942ffb8237d56c97451765ac3e2b16d6cb0d2c
       - pypi: https://files.pythonhosted.org/packages/02/be/5d2d47b1fb58943194fb59dcf222f7c4e35122ec0ffe8c36e18b5d728f0b/tblib-3.2.2-py3-none-any.whl
       - pypi: https://files.pythonhosted.org/packages/04/4b/29cac41a4d98d144bf5f6d33995617b185d14b22401f75ca86f384e87ff1/h11-0.16.0-py3-none-any.whl
@@ -5333,6 +5355,7 @@ environments:
       - pypi: https://files.pythonhosted.org/packages/54/20/4d324d65cc6d9205fabedc306948156824eb9f0ee1633355a8f7ec5c66bf/pluggy-1.6.0-py3-none-any.whl
       - pypi: https://files.pythonhosted.org/packages/56/6d/0d9848617b9f753b87f214f1c682592f7ca42de085f564352f10f0843026/ipywidgets-8.1.8-py3-none-any.whl
       - pypi: https://files.pythonhosted.org/packages/59/8c/77f5097695f4dd8255ecbd08b2a1ed8ba8b953d337804dd7080f199e12bf/tornado-6.5.5-cp39-abi3-macosx_10_9_universal2.whl
+      - pypi: https://files.pythonhosted.org/packages/5d/f3/1f8651f23101e6fae41d0d504414c9722b0140bf0fc6acf87ac52e18aa41/pyaml-26.2.1-py3-none-any.whl
       - pypi: https://files.pythonhosted.org/packages/5e/f5/0c41cb68dcae6b7de4fac4188a3a9589e21fb31df21ea3a2e888db95e6c9/soupsieve-2.8.4-py3-none-any.whl
       - pypi: https://files.pythonhosted.org/packages/60/97/891a0971e1e4a8c5d2b20bbe0e524dc04548d2307fee33cdeba148fd4fc7/comm-0.2.3-py3-none-any.whl
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@@ -5524,7 +5547,7 @@ environments:
       - conda: https://conda.anaconda.org/conda-forge/win-64/vcomp14-14.51.36231-h1b9f54f_37.conda
       - conda: https://conda.anaconda.org/conda-forge/win-64/zstd-1.5.7-h534d264_6.conda
       - pypi: .
-      - pypi: git+https://github.com/modflow-org/modflow-devtools#06e14c20c250bada77b3facb57fa3a286c4c211d
+      - pypi: git+https://github.com/modflow-org/modflow-devtools#5fde75e2b737b698795c30d993340f956350dbda
       - pypi: git+https://github.com/wpbonelli/xattree#82942ffb8237d56c97451765ac3e2b16d6cb0d2c
       - pypi: https://files.pythonhosted.org/packages/02/be/5d2d47b1fb58943194fb59dcf222f7c4e35122ec0ffe8c36e18b5d728f0b/tblib-3.2.2-py3-none-any.whl
       - pypi: https://files.pythonhosted.org/packages/04/4b/29cac41a4d98d144bf5f6d33995617b185d14b22401f75ca86f384e87ff1/h11-0.16.0-py3-none-any.whl
@@ -5578,6 +5601,7 @@ environments:
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       - pypi: https://files.pythonhosted.org/packages/5d/78/1b74c5bbb3f99b77a1715c91b3e0b5bdb6fe302d95ace4f5b1bec37b0167/charset_normalizer-3.4.7-cp313-cp313-win_amd64.whl
+      - pypi: https://files.pythonhosted.org/packages/5d/f3/1f8651f23101e6fae41d0d504414c9722b0140bf0fc6acf87ac52e18aa41/pyaml-26.2.1-py3-none-any.whl
       - pypi: https://files.pythonhosted.org/packages/5e/f5/0c41cb68dcae6b7de4fac4188a3a9589e21fb31df21ea3a2e888db95e6c9/soupsieve-2.8.4-py3-none-any.whl
       - pypi: https://files.pythonhosted.org/packages/60/97/891a0971e1e4a8c5d2b20bbe0e524dc04548d2307fee33cdeba148fd4fc7/comm-0.2.3-py3-none-any.whl
       - pypi: https://files.pythonhosted.org/packages/62/a1/3d680cbfd5f4b8f15abc1d571870c5fc3e594bb582bc3b64ea099db13e56/jinja2-3.1.6-py3-none-any.whl
@@ -9624,7 +9648,7 @@ packages:
   - build ; extra == 'build'
   - twine ; extra == 'build'
   requires_python: '>=3.11,<3.14'
-- pypi: git+https://github.com/modflow-org/modflow-devtools#06e14c20c250bada77b3facb57fa3a286c4c211d
+- pypi: git+https://github.com/modflow-org/modflow-devtools#5fde75e2b737b698795c30d993340f956350dbda
   name: modflow-devtools
   version: 1.10.0.dev1
   requires_dist:
@@ -9642,6 +9666,7 @@ packages:
   - numpy ; extra == 'dev'
   - pandas ; extra == 'dev'
   - pooch ; extra == 'dev'
+  - pyaml ; extra == 'dev'
   - pydantic ; extra == 'dev'
   - pytest!=8.1.0 ; extra == 'dev'
   - pytest-cov ; extra == 'dev'
@@ -9656,6 +9681,7 @@ packages:
   - tomli-w ; extra == 'dev'
   - boltons ; extra == 'dfn'
   - pooch ; extra == 'dfn'
+  - pyaml ; extra == 'dfn'
   - pydantic ; extra == 'dfn'
   - tomli ; extra == 'dfn'
   - tomli-w ; extra == 'dfn'
@@ -9665,6 +9691,7 @@ packages:
   - boltons ; extra == 'ecosystem'
   - filelock ; extra == 'ecosystem'
   - pooch ; extra == 'ecosystem'
+  - pyaml ; extra == 'ecosystem'
   - pydantic ; extra == 'ecosystem'
   - tomli ; extra == 'ecosystem'
   - tomli-w ; extra == 'ecosystem'
@@ -9674,6 +9701,7 @@ packages:
   - boltons ; extra == 'models'
   - filelock ; extra == 'models'
   - pooch ; extra == 'models'
+  - pyaml ; extra == 'models'
   - pydantic ; extra == 'models'
   - tomli ; extra == 'models'
   - tomli-w ; extra == 'models'
@@ -9693,7 +9721,7 @@ packages:
   - pyyaml ; extra == 'test'
   - ruff ; extra == 'test'
   - syrupy<5.0.0 ; extra == 'test'
-  requires_python: '>=3.10'
+  requires_python: '>=3.11'
 - pypi: git+https://github.com/wpbonelli/xattree#82942ffb8237d56c97451765ac3e2b16d6cb0d2c
   name: xattree
   version: 0.1.0.dev0
@@ -12599,6 +12627,14 @@ packages:
   version: 1.8.0
   sha256: 014a7e68d623e9a4222d663931febc3033c5c7c9730785727de2a81f87d5bab8
   requires_python: '>=3.9'
+- pypi: https://files.pythonhosted.org/packages/5d/f3/1f8651f23101e6fae41d0d504414c9722b0140bf0fc6acf87ac52e18aa41/pyaml-26.2.1-py3-none-any.whl
+  name: pyaml
+  version: 26.2.1
+  sha256: 6261c2f0a2f33245286c794ad6ec234be33a73d2b05427079fd343e2812a87cf
+  requires_dist:
+  - pyyaml
+  - unidecode ; extra == 'anchors'
+  requires_python: '>=3.8'
 - pypi: https://files.pythonhosted.org/packages/5e/f5/0c41cb68dcae6b7de4fac4188a3a9589e21fb31df21ea3a2e888db95e6c9/soupsieve-2.8.4-py3-none-any.whl
   name: soupsieve
   version: 2.8.4
diff --git a/test/test_mf6_codegen.py b/test/test_mf6_codegen.py
index cd700d90..c9bb7a32 100644
--- a/test/test_mf6_codegen.py
+++ b/test/test_mf6_codegen.py
@@ -18,9 +18,7 @@
 from pathlib import Path
 
 import pytest
-from modflow_devtools.dfns import load_flat
-from modflow_devtools.dfns.dfn2toml import convert as dfn2toml
-from modflow_devtools.dfns.schema.v2 import FieldV2
+from modflow_devtools.dfn import Dfn, Field
 
 from flopy4.mf6.component import COMPONENTS
 from flopy4.mf6.utils.codegen.filters import (
@@ -39,17 +37,9 @@
 
 # Shared fixtures
 @pytest.fixture(scope="session")
-def v2_dfn_dir(dfn_path, tmp_path_factory):
-    """Convert the session-level v1 DFN directory to v2 TOML once."""
-    v2dir = tmp_path_factory.mktemp("dfn_v2")
-    dfn2toml(dfn_path, v2dir)
-    return v2dir
-
-
-@pytest.fixture(scope="session")
-def all_dfns(v2_dfn_dir):
-    """Load all v2 DFNs as a flat dict."""
-    return load_flat(v2_dfn_dir)
+def all_dfns(dfn_path):
+    """Load all DFNs as a flat dict."""
+    return Dfn.load_all(dfn_path, schema_version="2.0.0.dev1")
 
 
 # Simple tier: Package subclasses with only scalars, arrays, and path records.
@@ -209,7 +199,7 @@ def test_safe_name(self, name, expected):
         ],
     )
     def test_py_type(self, ftype, shape, optional, expected):
-        f = FieldV2(name="x", type=ftype, block="options", shape=shape, optional=optional)
+        f = Field(name="x", type=ftype, block="options", shape=shape, optional=optional)
         assert py_type(f) == expected
 
     @pytest.mark.parametrize(
@@ -222,7 +212,7 @@ def test_py_type(self, ftype, shape, optional, expected):
     )
     def test_py_type_period_array_always_optional(self, ftype, shape):
         """Period arrays get Optional even when DFN marks them required."""
-        f = FieldV2(name="x", type=ftype, block="period", shape=shape, optional=False)
+        f = Field(name="x", type=ftype, block="period", shape=shape, optional=False)
         result = py_type(f)
         assert result.startswith("Optional["), (
             f"Expected Optional for period {ftype} array but got {result!r}"
@@ -241,13 +231,13 @@ def test_py_type_period_array_always_optional(self, ftype, shape):
         ],
     )
     def test_is_generatable(self, ftype, shape, generatable):
-        f = FieldV2(name="x", type=ftype, block="options", shape=shape)
+        f = Field(name="x", type=ftype, block="options", shape=shape)
         assert is_generatable(f) == generatable
 
     def test_is_generatable_file_record(self):
         """A record with a filein/fileout child is generatable as a path."""
-        child_in = FieldV2(name="filein", type="keyword", block="options")
-        f = FieldV2(
+        child_in = Field(name="filein", type="keyword", block="options")
+        f = Field(
             name="my_filerecord",
             type="record",
             block="options",
@@ -264,12 +254,12 @@ def test_is_generatable_file_record(self):
         ],
     )
     def test_spec_call_prefix(self, ftype, shape, check):
-        f = FieldV2(name="x", type=ftype, block="options", shape=shape)
+        f = Field(name="x", type=ftype, block="options", shape=shape)
         assert check(spec_call(f))
 
     def test_spec_call_file_record(self):
-        child = FieldV2(name="fileout", type="keyword", block="options")
-        f = FieldV2(
+        child = Field(name="fileout", type="keyword", block="options")
+        f = Field(
             name="budget_filerecord",
             type="record",
             block="options",
@@ -380,7 +370,7 @@ def test_lak_numeric_index_autodetects_cellid(all_dfns, dfn_path):
     """v1 DFN numeric_index=True on ifno/iconn auto-sets cellid; is_cellid stored as object."""
     if "gwf-lak" not in all_dfns:
         pytest.skip("gwf-lak not in DFN set")
-    v1_dfns = load_flat(dfn_path)
+    v1_dfns = Dfn.load_all(dfn_path, schema_version="2.0.0.dev1")
     spec = build_component_spec(
         all_dfns["gwf-lak"], root=Path("/fake"), v1_dfn=v1_dfns.get("gwf-lak")
     )
@@ -439,7 +429,7 @@ class TestBlockPropertySpec:
     def lak_spec(self, all_dfns, dfn_path):
         if "gwf-lak" not in all_dfns:
             pytest.skip("gwf-lak not in DFN set")
-        v1_dfns = load_flat(dfn_path)
+        v1_dfns = Dfn.load_all(dfn_path, schema_version="2.0.0.dev1")
         return build_component_spec(
             all_dfns["gwf-lak"], root=Path("/fake"), v1_dfn=v1_dfns.get("gwf-lak")
         )
@@ -519,7 +509,7 @@ def test_can_expand_record_all_keywords(all_dfns):
     """A record whose children are all keyword type (like cvoptions) is expandable."""
     if "gwf-npf" not in all_dfns:
         pytest.skip("gwf-npf not in DFN set")
-    cvoptions = all_dfns["gwf-npf"].blocks["options"]["cvoptions"]
+    cvoptions = all_dfns["gwf-npf"]["blocks"]["options"]["cvoptions"]
     assert can_expand_record(cvoptions)
 
 
@@ -529,7 +519,7 @@ def test_can_expand_record_with_positional_required_data(all_dfns):
         pytest.skip("gwf-npf not in DFN set")
     from flopy4.mf6.utils.codegen.filters import can_generate_record_class
 
-    rewet_record = all_dfns["gwf-npf"].blocks["options"]["rewet_record"]
+    rewet_record = all_dfns["gwf-npf"]["blocks"]["options"]["rewet_record"]
     assert not can_expand_record(rewet_record)
     assert can_generate_record_class(rewet_record)
 
@@ -540,7 +530,7 @@ def test_rcloserecord_generates_inner_class(all_dfns):
         pytest.skip("sln-ims not in DFN set")
     from flopy4.mf6.utils.codegen.filters import can_generate_record_class
 
-    rcloserecord = all_dfns["sln-ims"].blocks["linear"]["rcloserecord"]
+    rcloserecord = all_dfns["sln-ims"]["blocks"]["linear"]["rcloserecord"]
     assert can_generate_record_class(rcloserecord)
 
 
@@ -605,12 +595,12 @@ def test_npf_compound_records_expanded(all_dfns):
 
 
 # Layer 3: End-to-end generation
-def test_simple_tier_generates_importable_files(v2_dfn_dir, tmp_path, all_dfns):
+def test_simple_tier_generates_importable_files(dfn_path, tmp_path, all_dfns):
     """Run make_all() and verify each simple-tier file is importable with the right class."""
     (tmp_path / "gwf").mkdir()
 
-    skip = {n for n in load_flat(v2_dfn_dir) if n not in SIMPLE_TIER}
-    specs = make_all(dfndir=v2_dfn_dir, outdir=tmp_path, fmt=False, skip=skip)
+    skip = {n for n in all_dfns if n not in SIMPLE_TIER}
+    specs = make_all(dfndir=dfn_path, outdir=tmp_path, fmt=False, skip=skip)
 
     generated = {s.dfn_name: s for s in specs}
 
@@ -643,12 +633,12 @@ def test_simple_tier_generates_importable_files(v2_dfn_dir, tmp_path, all_dfns):
         assert hasattr(mod, expected_class), f"Class {expected_class} not found in {spec.outpath}"
 
 
-def test_solution_tier_generates_importable_files(v2_dfn_dir, tmp_path, all_dfns):
+def test_solution_tier_generates_importable_files(dfn_path, tmp_path, all_dfns):
     """Run make_all() and verify each solution-tier file is importable with Solution base."""
     from flopy4.mf6.solution import Solution
 
-    skip = {n for n in load_flat(v2_dfn_dir) if n not in SOLUTION_TIER}
-    specs = make_all(dfndir=v2_dfn_dir, outdir=tmp_path, fmt=False, skip=skip)
+    skip = {n for n in all_dfns if n not in SOLUTION_TIER}
+    specs = make_all(dfndir=dfn_path, outdir=tmp_path, fmt=False, skip=skip)
 
     generated = {s.dfn_name: s for s in specs}
 
@@ -700,14 +690,14 @@ def _load_class_from_spec(spec, mod_name: str, expected_class: str):
             del sys.modules[key]
 
 
-def test_transport_tier_generates_importable_files(v2_dfn_dir, tmp_path, all_dfns):
+def test_transport_tier_generates_importable_files(dfn_path, tmp_path, all_dfns):
     """gwt-disv, gwt-ist, gwe-disv generate importable Package subclasses."""
     for subdir in ("gwt", "gwe"):
         (tmp_path / subdir).mkdir()
 
     target = {n for n in TRANSPORT_TIER if n in all_dfns}
-    skip = {n for n in load_flat(v2_dfn_dir) if n not in target}
-    specs = make_all(dfndir=v2_dfn_dir, outdir=tmp_path, fmt=False, skip=skip)
+    skip = {n for n in all_dfns if n not in target}
+    specs = make_all(dfndir=dfn_path, outdir=tmp_path, fmt=False, skip=skip)
     generated = {s.dfn_name: s for s in specs}
 
     from flopy4.mf6.package import Package
@@ -722,14 +712,14 @@ def test_transport_tier_generates_importable_files(v2_dfn_dir, tmp_path, all_dfn
         assert issubclass(cls, Package)
 
 
-def test_oc_tier_generates_importable_files(v2_dfn_dir, tmp_path, all_dfns):
+def test_oc_tier_generates_importable_files(dfn_path, tmp_path, all_dfns):
     """gwt-oc, gwe-oc, prt-oc generate importable Package subclasses with OC period fields."""
     for subdir in ("gwt", "gwe", "prt"):
         (tmp_path / subdir).mkdir()
 
     target = {n for n in OC_TIER if n in all_dfns}
-    skip = {n for n in load_flat(v2_dfn_dir) if n not in target}
-    specs = make_all(dfndir=v2_dfn_dir, outdir=tmp_path, fmt=False, skip=skip)
+    skip = {n for n in all_dfns if n not in target}
+    specs = make_all(dfndir=dfn_path, outdir=tmp_path, fmt=False, skip=skip)
     generated = {s.dfn_name: s for s in specs}
 
     from flopy4.mf6.package import Package
@@ -747,13 +737,13 @@ def test_oc_tier_generates_importable_files(v2_dfn_dir, tmp_path, all_dfns):
         assert oc_fields, f"{dfn_name} should have save_/print_ period fields"
 
 
-def test_utl_tier_generates_importable_files(v2_dfn_dir, tmp_path, all_dfns):
+def test_utl_tier_generates_importable_files(dfn_path, tmp_path, all_dfns):
     """utl-* packages generate importable Package subclasses (including utl-tas inner classes)."""
     (tmp_path / "utl").mkdir()
 
     target = {n for n in UTL_TIER if n in all_dfns}
-    skip = {n for n in load_flat(v2_dfn_dir) if n not in target}
-    specs = make_all(dfndir=v2_dfn_dir, outdir=tmp_path, fmt=False, makedirs=True, skip=skip)
+    skip = {n for n in all_dfns if n not in target}
+    specs = make_all(dfndir=dfn_path, outdir=tmp_path, fmt=False, makedirs=True, skip=skip)
     generated = {s.dfn_name: s for s in specs}
 
     from flopy4.mf6.package import Package
@@ -768,13 +758,13 @@ def test_utl_tier_generates_importable_files(v2_dfn_dir, tmp_path, all_dfns):
         assert issubclass(cls, Package)
 
 
-def test_exg_tier_generates_importable_files(v2_dfn_dir, tmp_path, all_dfns):
+def test_exg_tier_generates_importable_files(dfn_path, tmp_path, all_dfns):
     """exg-* packages generate importable Package subclasses (including 0-field pass-only)."""
     (tmp_path / "exg").mkdir()
 
     target = {n for n in EXG_TIER if n in all_dfns}
-    skip = {n for n in load_flat(v2_dfn_dir) if n not in target}
-    specs = make_all(dfndir=v2_dfn_dir, outdir=tmp_path, fmt=False, makedirs=True, skip=skip)
+    skip = {n for n in all_dfns if n not in target}
+    specs = make_all(dfndir=dfn_path, outdir=tmp_path, fmt=False, makedirs=True, skip=skip)
     generated = {s.dfn_name: s for s in specs}
 
     from flopy4.mf6.package import Package
diff --git a/test/test_mf6_grammar_gen.py b/test/test_mf6_grammar_gen.py
index de6150b4..b4afe0b2 100644
--- a/test/test_mf6_grammar_gen.py
+++ b/test/test_mf6_grammar_gen.py
@@ -1,6 +1,5 @@
 import pytest
-from modflow_devtools.dfns import Dfn
-from modflow_devtools.dfns.schema.v2 import FieldV2
+from modflow_devtools.dfn import Dfn, Field
 from packaging.version import Version
 
 from flopy4.mf6.codec.reader.grammar import make_grammar, make_grammars
@@ -14,7 +13,7 @@ def minimal_dfn():
         name="test-component",
         blocks={
             "options": {
-                "test_field": FieldV2(
+                "test_field": Field(
                     name="test_field",
                     type="keyword",
                     block="options",
@@ -32,14 +31,14 @@ def simple_dfn():
         name="gwf-test",
         blocks={
             "options": {
-                "export_ascii": FieldV2(
+                "export_ascii": Field(
                     name="export_array_ascii",
                     type="keyword",
                     block="options",
                 )
             },
             "griddata": {
-                "strt": FieldV2(
+                "strt": Field(
                     name="strt",
                     type="double",
                     block="griddata",
@@ -147,20 +146,20 @@ def test_make_grammar_with_period_block(tmp_path):
         name="gwf-test",
         blocks={
             "options": {
-                "print_input": FieldV2(
+                "print_input": Field(
                     name="print_input",
                     type="keyword",
                     block="options",
                 )
             },
             "period": {
-                "q": FieldV2(
+                "q": Field(
                     name="q",
                     type="double",
                     block="period",
                     shape="(nper, nnodes)",
                 ),
-                "aux": FieldV2(
+                "aux": Field(
                     name="aux",
                     type="double",
                     block="period",
@@ -196,7 +195,7 @@ def test_make_grammar_with_named_subfields(tmp_path):
         name="gwf-rch",
         blocks={
             "period": {
-                "recharge": FieldV2(
+                "recharge": Field(
                     name="recharge",
                     type="double",
                     block="period",
@@ -226,21 +225,21 @@ def test_make_grammar_with_oc_style_records(tmp_path):
         name="gwf-oc",
         blocks={
             "period": {
-                "saverecord": FieldV2(
+                "saverecord": Field(
                     name="saverecord",
                     type="record",
                     block="period",
                     children={
-                        "save": FieldV2(name="save", type="keyword", block="period"),
-                        "rtype": FieldV2(name="rtype", type="string", block="period"),
-                        "ocsetting": FieldV2(
+                        "save": Field(name="save", type="keyword", block="period"),
+                        "rtype": Field(name="rtype", type="string", block="period"),
+                        "ocsetting": Field(
                             name="ocsetting",
                             type="union",
                             block="period",
                             children={
-                                "all": FieldV2(name="all", type="keyword", block="period"),
-                                "first": FieldV2(name="first", type="keyword", block="period"),
-                                "last": FieldV2(name="last", type="keyword", block="period"),
+                                "all": Field(name="all", type="keyword", block="period"),
+                                "first": Field(name="first", type="keyword", block="period"),
+                                "last": Field(name="last", type="keyword", block="period"),
                             },
                         ),
                     },
diff --git a/test/test_mf6_reader.py b/test/test_mf6_reader.py
index 3e0997ec..5b25fcc9 100644
--- a/test/test_mf6_reader.py
+++ b/test/test_mf6_reader.py
@@ -7,7 +7,7 @@
 import pytest
 import xarray as xr
 from lark import Lark
-from modflow_devtools.dfns import Dfn, MapV1To2, load_flat
+from modflow_devtools.dfn import Dfn
 from modflow_devtools.download import download_and_unzip
 from packaging.version import Version
 
@@ -239,8 +239,8 @@ def test_transform_layered_array():
 
 
 def test_transform_full_component():
-    dfn = Dfn.from_dict(
-        {
+    dfn = Dfn(
+        **{
             "name": "test_transform",
             "schema_version": Version("2"),
             "blocks": {
@@ -402,12 +402,8 @@ def test_parse_gwf_wel_file(model_workspace):
 def test_transform_gwf_ic_file(model_workspace, dfn_path):
     """Test transforming a parsed GWF IC file into structured data."""
 
-    # Load the DFN for IC and convert to V2
-    from modflow_devtools.dfns import MapV1To2
-
-    v1_dfns = load_flat(dfn_path)
-    mapper = MapV1To2()
-    ic_dfn = mapper.map(v1_dfns["gwf-ic"])
+    v1_dfns = Dfn.load_all(dfn_path, schema_version="2.0.0.dev1")
+    ic_dfn = v1_dfns["gwf-ic"]
 
     # Find the IC file
     ic_files = list(model_workspace.rglob("*.ic"))
@@ -444,12 +440,8 @@ def test_transform_gwf_ic_file(model_workspace, dfn_path):
 def test_transform_gwf_wel_file(model_workspace, dfn_path):
     """Test transforming a parsed GWF WEL file into structured data."""
 
-    # Load the DFN for WEL and convert to V2
-    from modflow_devtools.dfns import MapV1To2
-
-    v1_dfns = load_flat(dfn_path)
-    mapper = MapV1To2()
-    wel_dfn = mapper.map(v1_dfns["gwf-wel"])
+    v1_dfns = Dfn.load_all(dfn_path, schema_version="2.0.0.dev1")
+    wel_dfn = v1_dfns["gwf-wel"]
 
     # Find the WEL file
     wel_files = list(model_workspace.rglob("*.wel"))
@@ -532,12 +524,8 @@ def test_parse_gwf_oc_file(model_workspace):
 def test_transform_gwf_oc_file(model_workspace, dfn_path):
     """Test transforming a parsed GWF OC file into structured data."""
 
-    # Load the DFN for OC and convert to V2
-    from modflow_devtools.dfns import MapV1To2
-
-    v1_dfns = load_flat(dfn_path)
-    mapper = MapV1To2()
-    oc_dfn = mapper.map(v1_dfns["gwf-oc"])
+    v1_dfns = Dfn.load_all(dfn_path, schema_version="2.0.0.dev1")
+    oc_dfn = v1_dfns["gwf-oc"]
 
     # Find the OC file
     oc_files = list(model_workspace.rglob("*.oc"))
@@ -593,9 +581,8 @@ def test_transform_gwf_dis_file(model_workspace, dfn_path):
     """Test transforming a parsed GWF DIS file into structured data."""
 
     # Load the DFN for DIS and convert to V2
-    v1_dfns = load_flat(dfn_path)
-    mapper = MapV1To2()
-    dis_dfn = mapper.map(v1_dfns["gwf-dis"])
+    v1_dfns = Dfn.load_all(dfn_path, schema_version="2.0.0.dev1")
+    dis_dfn = v1_dfns["gwf-dis"]
 
     # Find the DIS file
     dis_files = list(model_workspace.rglob("*.dis"))
@@ -642,9 +629,8 @@ def test_transform_gwf_npf_file(model_workspace, dfn_path):
     """Test transforming a parsed GWF NPF file into structured data."""
 
     # Load the DFN for NPF and convert to V2
-    v1_dfns = load_flat(dfn_path)
-    mapper = MapV1To2()
-    npf_dfn = mapper.map(v1_dfns["gwf-npf"])
+    v1_dfns = Dfn.load_all(dfn_path, schema_version="2.0.0.dev1")
+    npf_dfn = v1_dfns["gwf-npf"]
 
     # Find the NPF file
     npf_files = list(model_workspace.rglob("*.npf"))
@@ -692,9 +678,8 @@ def test_transform_gwf_sto_file(model_workspace, dfn_path):
     """Test transforming a parsed GWF STO file into structured data."""
 
     # Load the DFN for STO and convert to V2
-    v1_dfns = load_flat(dfn_path)
-    mapper = MapV1To2()
-    sto_dfn = mapper.map(v1_dfns["gwf-sto"])
+    v1_dfns = Dfn.load_all(dfn_path, schema_version="2.0.0.dev1")
+    sto_dfn = v1_dfns["gwf-sto"]
 
     # Find the STO file
     sto_files = list(model_workspace.rglob("*.sto"))

From b36ee27d88512d014ccbdca8562aa78632b1b32e Mon Sep 17 00:00:00 2001
From: wpbonelli <wbonelli@ucar.edu>
Date: Sun, 31 May 2026 13:46:11 -0700
Subject: [PATCH 2/4] compat fixes

---
 flopy4/mf6/utils/codegen/filters.py |  8 ++++----
 flopy4/mf6/utils/codegen/make.py    | 12 +++++++++---
 2 files changed, 13 insertions(+), 7 deletions(-)

diff --git a/flopy4/mf6/utils/codegen/filters.py b/flopy4/mf6/utils/codegen/filters.py
index c973ca15..14b58920 100644
--- a/flopy4/mf6/utils/codegen/filters.py
+++ b/flopy4/mf6/utils/codegen/filters.py
@@ -81,7 +81,7 @@ def output_path(dfn_name: str, root: Path) -> Path:
 
 def has_period_block(dfn: Dfn) -> bool:
     """True if the DFN defines a period block (stress package)."""
-    return "period" in (dfn["blocks"] or {})
+    return "period" in (dfn.get("blocks") or {})
 
 
 def has_dimensions_block(dfn: Dfn) -> bool:
@@ -289,7 +289,7 @@ def list_col_dim(f: Field, dfn: Dfn) -> str | None:
     Falls back to the single entry in the DFN's dimensions block.
     Returns None when the dimension cannot be determined unambiguously.
     """
-    dim_block = (dfn["blocks"] or {}).get("dimensions", {})
+    dim_block = (dfn.get("blocks") or {}).get("dimensions", {})
     if shape := f.get("shape", None):
         inner = shape.strip().strip("()")
         parts = [p.strip() for p in inner.split(",") if p.strip()]
@@ -787,7 +787,7 @@ def block_schema(v1_dfn: Dfn, block_name: str) -> list[ColumnSpec]:
     its nested children (built by the v2.0.0.dev1 migration). Returns one
     ColumnSpec per column in DFN order.
     """
-    v1_block = (v1_dfn["blocks"] or {}).get(block_name) or {}
+    v1_block = (v1_dfn.get("blocks") or {}).get(block_name) or {}
     list_field = next((f for f in v1_block.values() if f.get("type") == "list"), None)
     if list_field is None:
         return []
@@ -832,7 +832,7 @@ def v1_list_block_names(v1_dfn: Dfn) -> list[str]:
     """
     seen: set[str] = set()
     result = []
-    for block_name, block in (v1_dfn["blocks"] or {}).items():
+    for block_name, block in (v1_dfn.get("blocks") or {}).items():
         if block_name in seen:
             continue
         if any(
diff --git a/flopy4/mf6/utils/codegen/make.py b/flopy4/mf6/utils/codegen/make.py
index a779ac5b..558ec87c 100644
--- a/flopy4/mf6/utils/codegen/make.py
+++ b/flopy4/mf6/utils/codegen/make.py
@@ -405,8 +405,8 @@ def _build_block_property_specs(
     block property API for each recarray block.  Returns (specs, block_names)
     where block_names is used as a skip-set in the main field loop.
     """
-    dfn_dims = set((dfn["blocks"] or {}).get("dimensions", {}).keys())
-    dfn_dims_ordered = list((dfn["blocks"] or {}).get("dimensions", {}).keys())
+    dfn_dims = set((dfn.get("blocks") or {}).get("dimensions", {}).keys())
+    dfn_dims_ordered = list((dfn.get("blocks") or {}).get("dimensions", {}).keys())
 
     # Collect v2 list blocks, excluding those handled by TOML overrides.
     list_fields_map: dict[str, Field | None] = {
@@ -832,7 +832,13 @@ def build_component_spec(
                 )
                 break
 
-    field_specs = prefix_specs + extra_specs + data_specs + period_specs
+    _seen_py_names: set[str] = set()
+    _deduped: list[FieldSpec] = []
+    for _fs in prefix_specs + extra_specs + data_specs + period_specs:
+        if _fs.py_name not in _seen_py_names:
+            _seen_py_names.add(_fs.py_name)
+            _deduped.append(_fs)
+    field_specs = _deduped
 
     # Build period_col_map: value columns in the period block (cellid/aux/boundname excluded).
     # Only packages with a standard stress-period list format produce a non-empty map.

From d334a20f0142e3fb2d0a7292048cb80863b5dfc4 Mon Sep 17 00:00:00 2001
From: wpbonelli <wbonelli@ucar.edu>
Date: Sun, 31 May 2026 18:07:23 -0700
Subject: [PATCH 3/4] regenerate mf6 module

---
 flopy4/mf6/gwe/est.py  |  6 +++---
 flopy4/mf6/gwe/ic.py   |  2 +-
 flopy4/mf6/gwe/lke.py  |  1 +
 flopy4/mf6/gwf/buy.py  |  4 +++-
 flopy4/mf6/gwf/chd.py  |  6 +++---
 flopy4/mf6/gwf/chdg.py |  8 ++++----
 flopy4/mf6/gwf/csub.py | 18 ++++++++++--------
 flopy4/mf6/gwf/drng.py |  6 +++---
 flopy4/mf6/gwf/evt.py  | 16 ++++++++--------
 flopy4/mf6/gwf/evta.py |  6 +++---
 flopy4/mf6/gwf/ghbg.py |  6 +++---
 flopy4/mf6/gwf/lak.py  | 10 +++++++++-
 flopy4/mf6/gwf/npf.py  | 20 ++++++++++----------
 flopy4/mf6/gwf/rcha.py |  2 +-
 flopy4/mf6/gwf/rivg.py |  8 ++++----
 flopy4/mf6/gwf/sto.py  |  8 ++++----
 flopy4/mf6/gwf/vsc.py  | 12 ++++++++----
 flopy4/mf6/gwf/welg.py |  2 +-
 flopy4/mf6/gwt/ic.py   |  2 +-
 flopy4/mf6/gwt/lkt.py  |  1 +
 flopy4/mf6/ims.py      |  6 +++---
 flopy4/mf6/prt/prp.py  |  4 ++--
 flopy4/mf6/utl/ats.py  |  2 +-
 flopy4/mf6/utl/spca.py |  2 +-
 24 files changed, 88 insertions(+), 70 deletions(-)

diff --git a/flopy4/mf6/gwe/est.py b/flopy4/mf6/gwe/est.py
index 792d9de0..ab1ba4b6 100644
--- a/flopy4/mf6/gwe/est.py
+++ b/flopy4/mf6/gwe/est.py
@@ -24,13 +24,13 @@ class Est(Package):
         block="options", default=False, longname="activate zero-order decay in solid phase"
     )
     density_water: Optional[float] = field(
-        block="options", default=None, longname="density of water"
+        block="options", default="1000.0", longname="density of water"
     )
     heat_capacity_water: Optional[float] = field(
-        block="options", default=None, longname="heat capacity of water"
+        block="options", default="4184.0", longname="heat capacity of water"
     )
     latent_heat_vaporization: Optional[float] = field(
-        block="options", default=None, longname="latent heat of vaporization"
+        block="options", default="2453500.0", longname="latent heat of vaporization"
     )
     porosity: NDArray[np.float64] = array(
         block="griddata",
diff --git a/flopy4/mf6/gwe/ic.py b/flopy4/mf6/gwe/ic.py
index ddf27ec1..ed4631f5 100644
--- a/flopy4/mf6/gwe/ic.py
+++ b/flopy4/mf6/gwe/ic.py
@@ -21,7 +21,7 @@ class Ic(Package):
     strt: NDArray[np.float64] = array(
         block="griddata",
         dims=("nodes",),
-        default=None,
+        default="0.0",
         netcdf=True,
         converter=Converter(structure_array, takes_self=True, takes_field=True),
         longname="starting temperature",
diff --git a/flopy4/mf6/gwe/lke.py b/flopy4/mf6/gwe/lke.py
index 820bec5d..e089a019 100644
--- a/flopy4/mf6/gwe/lke.py
+++ b/flopy4/mf6/gwe/lke.py
@@ -104,6 +104,7 @@ class Lke(Package):
         converter=Converter(structure_array, takes_self=True, takes_field=True),
         longname="lake name",
     )
+    # TODO: laksetting — type 'union' not yet supported
     status: Optional[NDArray[np.object_]] = embedded_keystring(
         "STATUS",
         "nlakes",
diff --git a/flopy4/mf6/gwf/buy.py b/flopy4/mf6/gwf/buy.py
index 1fe1dc7d..5e7bc5a1 100644
--- a/flopy4/mf6/gwf/buy.py
+++ b/flopy4/mf6/gwf/buy.py
@@ -20,7 +20,9 @@ class Buy(Package):
     hhformulation_rhs: bool = field(
         block="options", default=False, longname="hh formulation on right-hand side"
     )
-    denseref: Optional[float] = field(block="options", default=None, longname="reference density")
+    denseref: Optional[float] = field(
+        block="options", default="1000.", longname="reference density"
+    )
     density_file: Optional[Path] = path(
         block="options", default=None, converter=to_path, inout="fileout"
     )
diff --git a/flopy4/mf6/gwf/chd.py b/flopy4/mf6/gwf/chd.py
index c7b5bd31..67c16d01 100644
--- a/flopy4/mf6/gwf/chd.py
+++ b/flopy4/mf6/gwf/chd.py
@@ -31,17 +31,17 @@ class Chd(Package):
         block="options", default=False, longname="print input to listing file"
     )
     print_flows: bool = field(
-        block="options", default=False, longname="print chd flows to listing file"
+        block="options", default=False, longname="print CHD flows to listing file"
     )
     save_flows: bool = field(
-        block="options", default=False, longname="save chd flows to budget file"
+        block="options", default=False, longname="save CHD flows to budget file"
     )
     ts_file: Optional[Path] = path(block="options", default=None, converter=to_path, inout="filein")
     obs_file: Optional[Path] = path(
         block="options", default=None, converter=to_path, inout="filein"
     )
     dev_no_newton: bool = field(
-        block="options", default=False, longname="turn off newton for unconfined cells"
+        block="options", default=False, longname="turn off Newton for unconfined cells"
     )
     maxbound: Optional[int] = field(
         block="dimensions", default=None, init=False, longname="maximum number of constant heads"
diff --git a/flopy4/mf6/gwf/chdg.py b/flopy4/mf6/gwf/chdg.py
index bf4844b9..37e3d8bc 100644
--- a/flopy4/mf6/gwf/chdg.py
+++ b/flopy4/mf6/gwf/chdg.py
@@ -32,10 +32,10 @@ class Chdg(Package):
         block="options", default=False, longname="print input to listing file"
     )
     print_flows: bool = field(
-        block="options", default=False, longname="print chd flows to listing file"
+        block="options", default=False, longname="print CHD flows to listing file"
     )
     save_flows: bool = field(
-        block="options", default=False, longname="save chd flows to budget file"
+        block="options", default=False, longname="save CHD flows to budget file"
     )
     obs_file: Optional[Path] = path(
         block="options", default=None, converter=to_path, inout="filein"
@@ -44,7 +44,7 @@ class Chdg(Package):
         block="options", default=False, longname="export array variables to netcdf output files."
     )
     dev_no_newton: bool = field(
-        block="options", default=False, longname="turn off newton for unconfined cells"
+        block="options", default=False, longname="turn off Newton for unconfined cells"
     )
     maxbound: Optional[int] = field(
         block="dimensions",
@@ -56,7 +56,7 @@ class Chdg(Package):
     head: Optional[NDArray[np.float64]] = array(
         block="period",
         dims=("nper", "nodes"),
-        default=None,
+        default="3.e30",
         netcdf=True,
         converter=Converter(structure_array, takes_self=True, takes_field=True),
         on_setattr=update_maxbound,
diff --git a/flopy4/mf6/gwf/csub.py b/flopy4/mf6/gwf/csub.py
index d55bebf4..809f6a01 100644
--- a/flopy4/mf6/gwf/csub.py
+++ b/flopy4/mf6/gwf/csub.py
@@ -21,10 +21,12 @@ class Csub(Package):
     print_input: bool = field(
         block="options", default=False, longname="print input to listing file"
     )
-    save_flows: bool = field(block="options", default=False, longname="keyword to save csub flows")
-    gammaw: Optional[float] = field(block="options", default=None, longname="unit weight of water")
+    save_flows: bool = field(block="options", default=False, longname="keyword to save CSUB flows")
+    gammaw: Optional[float] = field(
+        block="options", default="9806.65", longname="unit weight of water"
+    )
     beta: Optional[float] = field(
-        block="options", default=None, longname="compressibility of water"
+        block="options", default="4.6512e-10", longname="compressibility of water"
     )
     head_based: bool = field(
         block="options",
@@ -42,7 +44,7 @@ class Csub(Package):
     compression_indices: bool = field(
         block="options",
         default=False,
-        longname="keyword to indicate cr and cc are read instead of sse and ssv",
+        longname="keyword to indicate CR and CC are read instead of SSE and SSV",
     )
     update_material_properties: bool = field(
         block="options",
@@ -106,7 +108,7 @@ class Csub(Package):
         block="options", default=None, converter=to_path, inout="filein"
     )
     ninterbeds: Optional[int] = dim(
-        block="dimensions", coord=False, default=None, longname="number of csub interbed systems"
+        block="dimensions", coord=False, default=None, longname="number of CSUB interbed systems"
     )
     maxsig0: Optional[int] = dim(
         block="dimensions",
@@ -199,12 +201,12 @@ class Csub(Package):
         dims=("ninterbeds",),
         default=None,
         converter=Converter(structure_array, takes_self=True, takes_field=True),
-        longname="well name",
+        longname="interbed name",
     )
     cg_ske_cr: NDArray[np.float64] = array(
         block="griddata",
         dims=("nodes",),
-        default=None,
+        default="1e-5",
         netcdf=True,
         converter=Converter(structure_array, takes_self=True, takes_field=True),
         longname="elastic coarse specific storage",
@@ -212,7 +214,7 @@ class Csub(Package):
     cg_theta: NDArray[np.float64] = array(
         block="griddata",
         dims=("nodes",),
-        default=None,
+        default="0.2",
         netcdf=True,
         converter=Converter(structure_array, takes_self=True, takes_field=True),
         longname="initial coarse-grained material porosity",
diff --git a/flopy4/mf6/gwf/drng.py b/flopy4/mf6/gwf/drng.py
index a4cdcf68..0f6768fd 100644
--- a/flopy4/mf6/gwf/drng.py
+++ b/flopy4/mf6/gwf/drng.py
@@ -38,7 +38,7 @@ class Drng(Package):
         block="options", default=False, longname="print calculated flows to listing file"
     )
     save_flows: bool = field(
-        block="options", default=False, longname="save drng flows to budget file"
+        block="options", default=False, longname="save DRNG flows to budget file"
     )
     obs_file: Optional[Path] = path(
         block="options", default=None, converter=to_path, inout="filein"
@@ -58,7 +58,7 @@ class Drng(Package):
     elev: Optional[NDArray[np.float64]] = array(
         block="period",
         dims=("nper", "nodes"),
-        default=None,
+        default="3.e30",
         netcdf=True,
         converter=Converter(structure_array, takes_self=True, takes_field=True),
         on_setattr=update_maxbound,
@@ -67,7 +67,7 @@ class Drng(Package):
     cond: Optional[NDArray[np.float64]] = array(
         block="period",
         dims=("nper", "nodes"),
-        default=None,
+        default="3.e30",
         netcdf=True,
         converter=Converter(structure_array, takes_self=True, takes_field=True),
         on_setattr=update_maxbound,
diff --git a/flopy4/mf6/gwf/evt.py b/flopy4/mf6/gwf/evt.py
index 2f98e838..e60ab1b2 100644
--- a/flopy4/mf6/gwf/evt.py
+++ b/flopy4/mf6/gwf/evt.py
@@ -48,7 +48,7 @@ class Evt(Package):
     surf_rate_specified: bool = field(
         block="options",
         default=False,
-        longname="specify proportion of evapotranspiration rate at et surface",
+        longname="specify proportion of evapotranspiration rate at ET surface",
     )
     maxbound: Optional[int] = field(
         block="dimensions",
@@ -57,7 +57,7 @@ class Evt(Package):
         longname="maximum number of evapotranspiration cells",
     )
     nseg: Optional[int] = dim(
-        block="dimensions", coord=False, default=None, longname="number of et segments"
+        block="dimensions", coord=False, default=None, longname="number of ET segments"
     )
     naux: Optional[int] = dim(block="__dim__", coord=False, default=None)
     surface: Optional[NDArray[np.float64]] = array(
@@ -66,7 +66,7 @@ class Evt(Package):
         default=None,
         converter=Converter(structure_array, takes_self=True, takes_field=True),
         on_setattr=update_maxbound,
-        longname="et surface",
+        longname="ET surface",
     )
     rate: Optional[NDArray[np.float64]] = array(
         block="period",
@@ -74,7 +74,7 @@ class Evt(Package):
         default=None,
         converter=Converter(structure_array, takes_self=True, takes_field=True),
         on_setattr=update_maxbound,
-        longname="maximum et rate",
+        longname="maximum ET rate",
     )
     depth: Optional[NDArray[np.float64]] = array(
         block="period",
@@ -82,7 +82,7 @@ class Evt(Package):
         default=None,
         converter=Converter(structure_array, takes_self=True, takes_field=True),
         on_setattr=update_maxbound,
-        longname="et extinction depth",
+        longname="ET extinction depth",
     )
     pxdp: Optional[NDArray[np.float64]] = array(
         block="period",
@@ -90,7 +90,7 @@ class Evt(Package):
         default=None,
         converter=Converter(structure_array, takes_self=True, takes_field=True),
         on_setattr=update_maxbound,
-        longname="proportion of et extinction depth",
+        longname="proportion of ET extinction depth",
     )
     petm: Optional[NDArray[np.float64]] = array(
         block="period",
@@ -98,7 +98,7 @@ class Evt(Package):
         default=None,
         converter=Converter(structure_array, takes_self=True, takes_field=True),
         on_setattr=update_maxbound,
-        longname="proportion of maximum et rate",
+        longname="proportion of maximum ET rate",
     )
     petm0: Optional[NDArray[np.float64]] = array(
         block="period",
@@ -106,7 +106,7 @@ class Evt(Package):
         default=None,
         converter=Converter(structure_array, takes_self=True, takes_field=True),
         on_setattr=update_maxbound,
-        longname="proportion of maximum et rate at et surface",
+        longname="proportion of maximum ET rate at ET surface",
     )
     aux: Optional[NDArray[np.float64]] = array(
         block="period",
diff --git a/flopy4/mf6/gwf/evta.py b/flopy4/mf6/gwf/evta.py
index 7f5d2bae..f7afbefb 100644
--- a/flopy4/mf6/gwf/evta.py
+++ b/flopy4/mf6/gwf/evta.py
@@ -60,7 +60,7 @@ class Evta(Package):
     surface: Optional[NDArray[np.float64]] = array(
         block="period",
         dims=("nper", "ncpl"),
-        default=None,
+        default="0.",
         netcdf=True,
         converter=Converter(structure_array, takes_self=True, takes_field=True),
         longname="evapotranspiration surface",
@@ -68,7 +68,7 @@ class Evta(Package):
     rate: Optional[NDArray[np.float64]] = array(
         block="period",
         dims=("nper", "ncpl"),
-        default=None,
+        default="1.e-3",
         netcdf=True,
         converter=Converter(structure_array, takes_self=True, takes_field=True),
         longname="evapotranspiration rate",
@@ -76,7 +76,7 @@ class Evta(Package):
     depth: Optional[NDArray[np.float64]] = array(
         block="period",
         dims=("nper", "ncpl"),
-        default=None,
+        default="1.0",
         netcdf=True,
         converter=Converter(structure_array, takes_self=True, takes_field=True),
         longname="extinction depth",
diff --git a/flopy4/mf6/gwf/ghbg.py b/flopy4/mf6/gwf/ghbg.py
index 3cd5aafa..df944428 100644
--- a/flopy4/mf6/gwf/ghbg.py
+++ b/flopy4/mf6/gwf/ghbg.py
@@ -35,7 +35,7 @@ class Ghbg(Package):
         block="options", default=False, longname="print calculated flows to listing file"
     )
     save_flows: bool = field(
-        block="options", default=False, longname="save ghbg flows to budget file"
+        block="options", default=False, longname="save GHBG flows to budget file"
     )
     obs_file: Optional[Path] = path(
         block="options", default=None, converter=to_path, inout="filein"
@@ -54,7 +54,7 @@ class Ghbg(Package):
     bhead: Optional[NDArray[np.float64]] = array(
         block="period",
         dims=("nper", "nodes"),
-        default=None,
+        default="3.e30",
         netcdf=True,
         converter=Converter(structure_array, takes_self=True, takes_field=True),
         on_setattr=update_maxbound,
@@ -63,7 +63,7 @@ class Ghbg(Package):
     cond: Optional[NDArray[np.float64]] = array(
         block="period",
         dims=("nper", "nodes"),
-        default=None,
+        default="3.e30",
         netcdf=True,
         converter=Converter(structure_array, takes_self=True, takes_field=True),
         on_setattr=update_maxbound,
diff --git a/flopy4/mf6/gwf/lak.py b/flopy4/mf6/gwf/lak.py
index 5872ffd7..3b639bac 100644
--- a/flopy4/mf6/gwf/lak.py
+++ b/flopy4/mf6/gwf/lak.py
@@ -56,7 +56,7 @@ class Lak(Package):
         block="options", default=None, longname="surface depression depth"
     )
     maximum_iterations: Optional[int] = field(
-        block="options", default=None, longname="lak newton-raphson iterations"
+        block="options", default=None, longname="LAK Newton-Raphson iterations"
     )
     maximum_stage_change: Optional[float] = field(
         block="options", default=None, longname="stage closure tolerance"
@@ -259,6 +259,14 @@ class Lak(Package):
         converter=Converter(structure_array, takes_self=True, takes_field=True),
         longname="bed slope",
     )
+    number: Optional[NDArray[np.int64]] = array(
+        block="period",
+        dims=("nper",),
+        default=None,
+        converter=Converter(structure_array, takes_self=True, takes_field=True),
+        longname="lake or outlet number for this entry",
+    )
+    # TODO: laksetting — type 'union' not yet supported
     status: Optional[NDArray[np.object_]] = embedded_keystring(
         "STATUS",
         "nlakes",
diff --git a/flopy4/mf6/gwf/npf.py b/flopy4/mf6/gwf/npf.py
index edf81461..5daa84fd 100644
--- a/flopy4/mf6/gwf/npf.py
+++ b/flopy4/mf6/gwf/npf.py
@@ -35,26 +35,26 @@ class Xt3doptions(Record):
         _keyword: ClassVar[str] = "xt3d"
         rhs: Optional[bool] = attrs.field(default=None)
 
-    save_flows: bool = field(block="options", default=False, longname="keyword to save npf flows")
+    save_flows: bool = field(block="options", default=False, longname="keyword to save NPF flows")
     print_flows: bool = field(
-        block="options", default=False, longname="keyword to print npf flows to listing file"
+        block="options", default=False, longname="keyword to print NPF flows to listing file"
     )
     alternative_cell_averaging: Optional[str] = field(
         block="options", default=None, longname="conductance weighting option"
     )
     thickstrt: bool = field(
-        block="options", default=False, longname="keyword to activate thickstrt option"
+        block="options", default=False, longname="keyword to activate THICKSTRT option"
     )
     cvoptions: Optional[Cvoptions] = field(block="options", default=None)
     perched: bool = field(
-        block="options", default=False, longname="keyword to activate perched option"
+        block="options", default=False, longname="keyword to activate PERCHED option"
     )
     rewet: Optional[Rewet] = field(block="options", default=None)
     xt3doptions: Optional[Xt3doptions] = field(block="options", default=None)
     highest_cell_saturation: bool = field(
         block="options",
         default=False,
-        longname="keyword to activate highest_cell_saturation option",
+        longname="keyword to activate HIGHEST_CELL_SATURATION option",
     )
     save_specific_discharge: bool = field(
         block="options", default=False, longname="keyword to save specific discharge"
@@ -63,10 +63,10 @@ class Xt3doptions(Record):
         block="options", default=False, longname="keyword to save saturation"
     )
     k22overk: bool = field(
-        block="options", default=False, longname="keyword to indicate that specified k22 is a ratio"
+        block="options", default=False, longname="keyword to indicate that specified K22 is a ratio"
     )
     k33overk: bool = field(
-        block="options", default=False, longname="keyword to indicate that specified k33 is a ratio"
+        block="options", default=False, longname="keyword to indicate that specified K33 is a ratio"
     )
     tvk_file: Optional[Path] = path(
         block="options", default=None, converter=to_path, inout="filein"
@@ -78,7 +78,7 @@ class Xt3doptions(Record):
         block="options", default=False, longname="export array variables to netcdf output files."
     )
     dev_no_newton: bool = field(
-        block="options", default=False, longname="turn off newton for unconfined cells"
+        block="options", default=False, longname="turn off Newton for unconfined cells"
     )
     dev_omega: Optional[float] = field(
         block="options", default=None, longname="set saturation omega value"
@@ -97,7 +97,7 @@ class Xt3doptions(Record):
         default=1.0,
         netcdf=True,
         converter=Converter(structure_array, takes_self=True, takes_field=True),
-        longname="hydraulic conductivity (l/t)",
+        longname="hydraulic conductivity (L/T)",
     )
     k22: Optional[NDArray[np.float64]] = array(
         block="griddata",
@@ -113,7 +113,7 @@ class Xt3doptions(Record):
         default=None,
         netcdf=True,
         converter=Converter(structure_array, takes_self=True, takes_field=True),
-        longname="hydraulic conductivity of third ellipsoid axis (l/t)",
+        longname="hydraulic conductivity of third ellipsoid axis (L/T)",
     )
     angle1: Optional[NDArray[np.float64]] = array(
         block="griddata",
diff --git a/flopy4/mf6/gwf/rcha.py b/flopy4/mf6/gwf/rcha.py
index 61a14393..a47616b3 100644
--- a/flopy4/mf6/gwf/rcha.py
+++ b/flopy4/mf6/gwf/rcha.py
@@ -60,7 +60,7 @@ class Rcha(Package):
     recharge: Optional[NDArray[np.float64]] = array(
         block="period",
         dims=("nper", "ncpl"),
-        default=None,
+        default="1.e-3",
         netcdf=True,
         converter=Converter(structure_array, takes_self=True, takes_field=True),
         longname="recharge rate",
diff --git a/flopy4/mf6/gwf/rivg.py b/flopy4/mf6/gwf/rivg.py
index 9261f59b..b2077610 100644
--- a/flopy4/mf6/gwf/rivg.py
+++ b/flopy4/mf6/gwf/rivg.py
@@ -35,7 +35,7 @@ class Rivg(Package):
         block="options", default=False, longname="print calculated flows to listing file"
     )
     save_flows: bool = field(
-        block="options", default=False, longname="save riv flows to budget file"
+        block="options", default=False, longname="save RIV flows to budget file"
     )
     obs_file: Optional[Path] = path(
         block="options", default=None, converter=to_path, inout="filein"
@@ -54,7 +54,7 @@ class Rivg(Package):
     stage: Optional[NDArray[np.float64]] = array(
         block="period",
         dims=("nper", "nodes"),
-        default=None,
+        default="3.e30",
         netcdf=True,
         converter=Converter(structure_array, takes_self=True, takes_field=True),
         on_setattr=update_maxbound,
@@ -63,7 +63,7 @@ class Rivg(Package):
     cond: Optional[NDArray[np.float64]] = array(
         block="period",
         dims=("nper", "nodes"),
-        default=None,
+        default="3.e30",
         netcdf=True,
         converter=Converter(structure_array, takes_self=True, takes_field=True),
         on_setattr=update_maxbound,
@@ -72,7 +72,7 @@ class Rivg(Package):
     rbot: Optional[NDArray[np.float64]] = array(
         block="period",
         dims=("nper", "nodes"),
-        default=None,
+        default="3.e30",
         netcdf=True,
         converter=Converter(structure_array, takes_self=True, takes_field=True),
         on_setattr=update_maxbound,
diff --git a/flopy4/mf6/gwf/sto.py b/flopy4/mf6/gwf/sto.py
index 873cf994..ff72afbb 100644
--- a/flopy4/mf6/gwf/sto.py
+++ b/flopy4/mf6/gwf/sto.py
@@ -16,11 +16,11 @@
 
 @xattree(kw_only=True)
 class Sto(Package):
-    save_flows: bool = field(block="options", default=False, longname="keyword to save npf flows")
+    save_flows: bool = field(block="options", default=False, longname="keyword to save NPF flows")
     storagecoefficient: bool = field(
         block="options",
         default=False,
-        longname="keyword to indicate ss is read as storage coefficient",
+        longname="keyword to indicate SS is read as storage coefficient",
     )
     ss_confined_only: bool = field(
         block="options",
@@ -55,7 +55,7 @@ class Sto(Package):
     ss: NDArray[np.float64] = array(
         block="griddata",
         dims=("nodes",),
-        default=None,
+        default="1.e-5",
         netcdf=True,
         converter=Converter(structure_array, takes_self=True, takes_field=True),
         longname="specific storage",
@@ -63,7 +63,7 @@ class Sto(Package):
     sy: NDArray[np.float64] = array(
         block="griddata",
         dims=("nodes",),
-        default=None,
+        default="0.15",
         netcdf=True,
         converter=Converter(structure_array, takes_self=True, takes_field=True),
         longname="specific yield",
diff --git a/flopy4/mf6/gwf/vsc.py b/flopy4/mf6/gwf/vsc.py
index bf87154c..1644336b 100644
--- a/flopy4/mf6/gwf/vsc.py
+++ b/flopy4/mf6/gwf/vsc.py
@@ -17,7 +17,7 @@
 
 @xattree(kw_only=True)
 class Vsc(Package):
-    viscref: Optional[float] = field(block="options", default=None, longname="reference viscosity")
+    viscref: Optional[float] = field(block="options", default="1.0", longname="reference viscosity")
     temperature_species_name: Optional[str] = field(
         block="options", default=None, longname="auxspeciesname that corresponds to temperature"
     )
@@ -27,13 +27,17 @@ class Vsc(Package):
         longname="keyword to specify viscosity formulation for the temperature species",
     )
     thermal_a2: Optional[float] = field(
-        block="options", default=None, longname="coefficient used in nonlinear viscosity function"
+        block="options", default="10.", longname="coefficient used in nonlinear viscosity function"
     )
     thermal_a3: Optional[float] = field(
-        block="options", default=None, longname="coefficient used in nonlinear viscosity function"
+        block="options",
+        default="248.37",
+        longname="coefficient used in nonlinear viscosity function",
     )
     thermal_a4: Optional[float] = field(
-        block="options", default=None, longname="coefficient used in nonlinear viscosity function"
+        block="options",
+        default="133.15",
+        longname="coefficient used in nonlinear viscosity function",
     )
     viscosity_file: Optional[Path] = path(
         block="options", default=None, converter=to_path, inout="fileout"
diff --git a/flopy4/mf6/gwf/welg.py b/flopy4/mf6/gwf/welg.py
index 8aab79a4..a4996f12 100644
--- a/flopy4/mf6/gwf/welg.py
+++ b/flopy4/mf6/gwf/welg.py
@@ -63,7 +63,7 @@ class Welg(Package):
     q: Optional[NDArray[np.float64]] = array(
         block="period",
         dims=("nper", "nodes"),
-        default=None,
+        default="3.e30",
         netcdf=True,
         converter=Converter(structure_array, takes_self=True, takes_field=True),
         on_setattr=update_maxbound,
diff --git a/flopy4/mf6/gwt/ic.py b/flopy4/mf6/gwt/ic.py
index 57d36e4e..12175e47 100644
--- a/flopy4/mf6/gwt/ic.py
+++ b/flopy4/mf6/gwt/ic.py
@@ -21,7 +21,7 @@ class Ic(Package):
     strt: NDArray[np.float64] = array(
         block="griddata",
         dims=("nodes",),
-        default=None,
+        default="0.0",
         netcdf=True,
         converter=Converter(structure_array, takes_self=True, takes_field=True),
         longname="starting concentration",
diff --git a/flopy4/mf6/gwt/lkt.py b/flopy4/mf6/gwt/lkt.py
index 758b29bc..c78d015b 100644
--- a/flopy4/mf6/gwt/lkt.py
+++ b/flopy4/mf6/gwt/lkt.py
@@ -90,6 +90,7 @@ class Lkt(Package):
         converter=Converter(structure_array, takes_self=True, takes_field=True),
         longname="lake name",
     )
+    # TODO: laksetting — type 'union' not yet supported
     status: Optional[NDArray[np.object_]] = embedded_keystring(
         "STATUS",
         "nlakes",
diff --git a/flopy4/mf6/ims.py b/flopy4/mf6/ims.py
index 22bc6bbd..61af2727 100644
--- a/flopy4/mf6/ims.py
+++ b/flopy4/mf6/ims.py
@@ -56,7 +56,7 @@ class Rclose(Record):
     under_relaxation_gamma: Optional[float] = field(
         block="nonlinear",
         default=None,
-        longname="relaxation factor for simple or the history or memory term factor for the cooley and delta-bar-delta algorithms",
+        longname="relaxation factor for SIMPLE or the history or memory term factor for the Cooley and delta-bar-delta algorithms",
     )
     under_relaxation_theta: Optional[float] = field(
         block="nonlinear", default=None, longname="under relaxation reduction factor"
@@ -95,10 +95,10 @@ class Rclose(Record):
     rclose: Optional[Rclose] = field(block="linear", default=None)
     linear_acceleration: str = field(block="linear", longname="linear acceleration method")
     relaxation_factor: Optional[float] = field(
-        block="linear", default=None, longname="relaxation factor used by ilu factorization"
+        block="linear", default=None, longname="relaxation factor used by ILU factorization"
     )
     preconditioner_levels: Optional[int] = field(
-        block="linear", default=None, longname="level of fill for ilu decomposition"
+        block="linear", default=None, longname="level of fill for ILU decomposition"
     )
     preconditioner_drop_tolerance: Optional[float] = field(
         block="linear", default=None, longname="drop tolerance used to drop preconditioner terms"
diff --git a/flopy4/mf6/prt/prp.py b/flopy4/mf6/prt/prp.py
index 92409084..3ce9117c 100644
--- a/flopy4/mf6/prt/prp.py
+++ b/flopy4/mf6/prt/prp.py
@@ -38,7 +38,7 @@ class ReleaseTimesfile(Record):
         block="options", default=None, longname="exit solve method"
     )
     exit_solve_tolerance: Optional[float] = field(
-        block="options", default=None, longname="exit solve tolerance"
+        block="options", default="1e-5", longname="exit solve tolerance"
     )
     local_z: bool = field(
         block="options", default=False, longname="whether to use local z coordinates"
@@ -76,7 +76,7 @@ class ReleaseTimesfile(Record):
         block="options", default=None, longname="release time frequency"
     )
     coordinate_check_method: Optional[str] = field(
-        block="options", default=None, longname="coordinate checking method"
+        block="options", default="eager", longname="coordinate checking method"
     )
     dev_cycle_detection_window: Optional[int] = field(
         block="options", default=None, longname="cycle detection window size"
diff --git a/flopy4/mf6/utl/ats.py b/flopy4/mf6/utl/ats.py
index 11510d88..0b611d8d 100644
--- a/flopy4/mf6/utl/ats.py
+++ b/flopy4/mf6/utl/ats.py
@@ -15,7 +15,7 @@
 @xattree(kw_only=True)
 class Ats(Package):
     maxats: Optional[int] = dim(
-        block="dimensions", coord=False, default=None, longname="number of ats periods"
+        block="dimensions", coord=False, default="1", longname="number of ATS periods"
     )
     iperats: Optional[NDArray[np.int64]] = array(
         block="perioddata",
diff --git a/flopy4/mf6/utl/spca.py b/flopy4/mf6/utl/spca.py
index 0a6b22e7..ad6c79fc 100644
--- a/flopy4/mf6/utl/spca.py
+++ b/flopy4/mf6/utl/spca.py
@@ -18,7 +18,7 @@
 class Spca(Package):
     multi_package: ClassVar[bool] = True
 
-    readasarrays: bool = field(block="options", default=False, longname="use array-based input")
+    readasarrays: bool = field(block="options", default=True, longname="use array-based input")
     print_input: bool = field(
         block="options", default=False, longname="print input to listing file"
     )

From 9ba64713fa601f7302e40e961898eefdd87c65a1 Mon Sep 17 00:00:00 2001
From: wpbonelli <wbonelli@ucar.edu>
Date: Sun, 31 May 2026 18:23:24 -0700
Subject: [PATCH 4/4] don't fill arrays with default val

---
 flopy4/mf6/converter/ingress/structure.py | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/flopy4/mf6/converter/ingress/structure.py b/flopy4/mf6/converter/ingress/structure.py
index 8f6afc9b..d19261a0 100644
--- a/flopy4/mf6/converter/ingress/structure.py
+++ b/flopy4/mf6/converter/ingress/structure.py
@@ -1003,7 +1003,7 @@ def structure_array(
                     coords,
                     list(coords_dict.values()),
                     shape=shape,
-                    fill_value=field.default or FILL_DNODATA,
+                    fill_value=FILL_DNODATA,
                 )
             else:
                 # Empty dict - return empty sparse array
@@ -1011,7 +1011,7 @@ def structure_array(
                     np.empty((len(shape), 0), dtype=int),
                     [],
                     shape=shape,
-                    fill_value=field.default or FILL_DNODATA,
+                    fill_value=FILL_DNODATA,
                 )
         else:
             # Dense approach
@@ -1086,10 +1086,6 @@ def structure_array(
                             # For multi-dimensional arrays with object dtype, store the object
                             result[kper] = val
 
-            # Apply fill value replacement (skip for object dtypes)
-            if field.dtype != np.object_:
-                result[result == FILL_DNODATA] = field.default or FILL_DNODATA
-
     elif isinstance(value, list):
         # List format
         result = _parse_list_format(value, dims_names, tuple(shape), field)