diff --git a/backend/app/models/llm/constants.py b/backend/app/models/llm/constants.py
index a604d2a50..1a0dca634 100644
--- a/backend/app/models/llm/constants.py
+++ b/backend/app/models/llm/constants.py
@@ -32,6 +32,9 @@
     ],
 }
 
+# OpenAI models that support reasoning (effort parameter)
+OPENAI_REASONING_MODELS: set[str] = {"o1", "o1-preview", "o1-mini"}
+
 SUPPORTED_VOICES = {
     ("google", "tts"): ["Kore", "Orus", "Leda", "Charon"],
     ("sarvamai", "tts"): ["simran", "shubh", "roopa"],
diff --git a/backend/app/services/llm/mappers.py b/backend/app/services/llm/mappers.py
index e69b744b7..19cbd7d04 100644
--- a/backend/app/services/llm/mappers.py
+++ b/backend/app/services/llm/mappers.py
@@ -1,4 +1,3 @@
-import litellm
 import logging
 
 from app.models.llm import KaapiCompletionConfig, NativeCompletionConfig
@@ -7,6 +6,7 @@
     BCP47_TO_ELEVENLABS_LANG,
     ELEVENLABS_VOICE_TO_ID,
     DEFAULT_TTS_VOICE,
+    OPENAI_REASONING_MODELS,
 )
 
 logger = logging.getLogger(__name__)
@@ -67,7 +67,7 @@ def map_kaapi_to_openai_params(kaapi_params: dict) -> tuple[dict, list[str]]:
     knowledge_base_ids = kaapi_params.get("knowledge_base_ids")
     max_num_results = kaapi_params.get("max_num_results")
 
-    support_reasoning = litellm.supports_reasoning(model=f"openai/{model}")
+    support_reasoning = model in OPENAI_REASONING_MODELS
 
     # Handle reasoning vs temperature mutual exclusivity
     if support_reasoning:
diff --git a/backend/pyproject.toml b/backend/pyproject.toml
index 769ac259f..6f9be27ee 100644
--- a/backend/pyproject.toml
+++ b/backend/pyproject.toml
@@ -53,6 +53,8 @@ override-dependencies = [
     "cryptography>=46.0.5",
     "werkzeu>=3.1.6",
     "pypdf>=3.9.0",
+    # Pinned: avoid supply chain attack in litellm 1.82.7/1.82.8 (Mar 2026)
+    "litellm==1.82.1",
 ]
 dev-dependencies = [
     "pytest<8.0.0,>=7.4.3",
diff --git a/backend/uv.lock b/backend/uv.lock
index 5ef8d7d9f..ed90bd176 100644
--- a/backend/uv.lock
+++ b/backend/uv.lock
@@ -1,5 +1,5 @@
 version = 1
-revision = 3
+revision = 2
 requires-python = ">=3.12, <4.0"
 resolution-markers = [
     "python_full_version >= '3.14' and sys_platform == 'win32'",
@@ -16,6 +16,7 @@ resolution-markers = [
 [manifest]
 overrides = [
     { name = "cryptography", specifier = ">=46.0.5" },
+    { name = "litellm", specifier = "==1.82.1" },
     { name = "pillow", specifier = ">=12.1.1" },
     { name = "pypdf", specifier = ">=3.9.0" },
     { name = "werkzeu", specifier = ">=3.1.6" },