Cycles Python Client

Python client for the Cycles budget-management protocol.

Installation

pip install runcycles

Quick Start

Decorator-based (recommended)

from runcycles import CyclesClient, CyclesConfig, cycles, get_cycles_context, CyclesMetrics

config = CyclesConfig(
    base_url="http://localhost:7878",
    api_key="your-api-key",
    tenant="acme",
)
client = CyclesClient(config)

@cycles(
    estimate=lambda prompt, tokens: tokens * 10,
    actual=lambda result: len(result) * 5,
    action_kind="llm.completion",
    action_name="gpt-4",
    client=client,
)
def call_llm(prompt: str, tokens: int) -> str:
    # Access the reservation context inside the guarded function
    ctx = get_cycles_context()
    if ctx and ctx.has_caps():
        tokens = min(tokens, ctx.caps.max_tokens or tokens)

    result = f"Response to: {prompt}"

    # Report metrics (included in the commit)
    if ctx:
        ctx.metrics = CyclesMetrics(tokens_input=tokens, tokens_output=len(result))

    return result

result = call_llm("Hello", tokens=100)

Need an API key? API keys are created via the Cycles Admin Server (port 7979). See the deployment guide to create one, or run:

curl -s -X POST http://localhost:7979/v1/admin/api-keys \
  -H "Content-Type: application/json" \
  -H "X-Admin-API-Key: admin-bootstrap-key" \
  -d '{"tenant_id":"acme-corp","name":"dev-key","permissions":["reservations:create","reservations:commit","reservations:release","reservations:extend","reservations:list","balances:read","decide","events:create"]}' | jq -r '.key_secret'

The key (e.g. cyc_live_abc123...) is shown only once — save it immediately. For key rotation and lifecycle details, see API Key Management.

Budget lifecycle

The @cycles decorator wraps your function in a reserve → execute → commit/release lifecycle:

Scenario	Outcome	Detail
Reservation denied	Neither	BudgetExceededError, OverdraftLimitExceededError, or DebtOutstandingError raised; function never executes
dry_run=True, any decision	Neither	Returns DryRunResult or raises; no real reservation created
Function returns successfully	Commit	Actual amount charged; unused remainder auto-released
Function raises any exception	Release	Full reserved amount returned to budget; exception re-raised
Commit fails (5xx / network)	Retry	Exponential backoff with configurable attempts
Commit fails (non-retryable 4xx)	Release	Reservation released after non-retryable client error
Commit gets RESERVATION_EXPIRED	Neither	Server already reclaimed budget on TTL expiry
Commit gets RESERVATION_FINALIZED	Neither	Already committed or released (idempotent replay)
Commit gets IDEMPOTENCY_MISMATCH	Neither	Previous commit already processed; no release attempted

All raised exceptions from the guarded function trigger release. See How Reserve-Commit Works for the full protocol-level explanation.

Programmatic client

from runcycles import (
    CyclesClient, CyclesConfig, ReservationCreateRequest,
    CommitRequest, Subject, Action, Amount, Unit, CyclesMetrics,
)

config = CyclesConfig(base_url="http://localhost:7878", api_key="your-api-key")

with CyclesClient(config) as client:
    # 1. Reserve budget
    response = client.create_reservation(ReservationCreateRequest(
        idempotency_key="req-001",
        subject=Subject(tenant="acme", agent="support-bot"),
        action=Action(kind="llm.completion", name="gpt-4"),
        estimate=Amount(unit=Unit.USD_MICROCENTS, amount=500_000),
        ttl_ms=30_000,
    ))

    if response.is_success:
        reservation_id = response.get_body_attribute("reservation_id")

        # 2. Do work ...

        # 3. Commit actual usage
        client.commit_reservation(reservation_id, CommitRequest(
            idempotency_key="commit-001",
            actual=Amount(unit=Unit.USD_MICROCENTS, amount=420_000),
            metrics=CyclesMetrics(tokens_input=1200, tokens_output=800),
        ))

Async support

from runcycles import AsyncCyclesClient, CyclesConfig, cycles

config = CyclesConfig(base_url="http://localhost:7878", api_key="your-api-key")
client = AsyncCyclesClient(config)

@cycles(estimate=1000, client=client)
async def call_llm(prompt: str) -> str:
    return f"Response to: {prompt}"

# In an async context:
result = await call_llm("Hello")

Configuration

From environment variables

from runcycles import CyclesConfig

config = CyclesConfig.from_env()
# Reads: CYCLES_BASE_URL, CYCLES_API_KEY, CYCLES_TENANT, etc.

Need an API key? See the deployment guide or API Key Management.

All options

CyclesConfig(
    base_url="http://localhost:7878",
    api_key="your-api-key",
    tenant="acme",
    workspace="prod",
    app="chat",
    workflow="refund-flow",
    agent="planner",
    toolset="search-tools",
    connect_timeout=2.0,
    read_timeout=5.0,
    retry_enabled=True,
    retry_max_attempts=5,
    retry_initial_delay=0.5,
    retry_multiplier=2.0,
    retry_max_delay=30.0,
)

Default client / config

Instead of passing client= to every @cycles decorator, set a module-level default:

from runcycles import CyclesConfig, set_default_config, set_default_client, CyclesClient, cycles

# Option 1: Set a config (client created lazily)
set_default_config(CyclesConfig(base_url="http://localhost:7878", api_key="your-key", tenant="acme"))

# Option 2: Set an explicit client
set_default_client(CyclesClient(CyclesConfig(base_url="http://localhost:7878", api_key="your-key")))

# Now @cycles works without client=
@cycles(estimate=1000)
def my_func() -> str:
    return "hello"

Error handling

from runcycles import (
    CyclesClient, CyclesConfig, ReservationCreateRequest,
    Subject, Action, Amount, Unit,
)

config = CyclesConfig(base_url="http://localhost:7878", api_key="your-key")

with CyclesClient(config) as client:
    response = client.create_reservation(ReservationCreateRequest(
        idempotency_key="req-002",
        subject=Subject(tenant="acme"),
        action=Action(kind="llm.completion", name="gpt-4"),
        estimate=Amount(unit=Unit.USD_MICROCENTS, amount=500_000),
    ))

    if response.is_transport_error:
        print(f"Transport error: {response.error_message}")
    elif not response.is_success:
        print(f"Error {response.status}: {response.error_message}")
        print(f"Request ID: {response.request_id}")

With the @cycles decorator, protocol errors are raised as typed exceptions:

from runcycles import cycles, BudgetExceededError, CyclesProtocolError

@cycles(estimate=1000, client=client)
def guarded_func() -> str:
    return "result"

try:
    guarded_func()
except BudgetExceededError:
    print("Budget exhausted — degrade or queue")
except CyclesProtocolError as e:
    if e.is_retryable() and e.retry_after_ms:
        print(f"Retry after {e.retry_after_ms}ms")
    print(f"Protocol error: {e}, code: {e.error_code}")

Exception hierarchy:

Exception	When
CyclesError	Base for all Cycles errors
CyclesProtocolError	Server returned a protocol-level error
BudgetExceededError	Budget insufficient for the reservation
OverdraftLimitExceededError	Debt exceeds the overdraft limit
DebtOutstandingError	Outstanding debt blocks new reservations
ReservationExpiredError	Operating on an expired reservation
ReservationFinalizedError	Operating on an already-committed/released reservation
CyclesTransportError	Network-level failure (connection, DNS, timeout)

Preflight checks (decide)

Check whether a reservation would be allowed without creating one:

from runcycles import DecisionRequest, Subject, Action, Amount, Unit

response = client.decide(DecisionRequest(
    idempotency_key="decide-001",
    subject=Subject(tenant="acme"),
    action=Action(kind="llm.completion", name="gpt-4"),
    estimate=Amount(unit=Unit.USD_MICROCENTS, amount=500_000),
))

if response.is_success:
    decision = response.get_body_attribute("decision")  # "ALLOW" or "DENY"
    print(f"Decision: {decision}")

Events (direct debit)

Record usage without a reservation — useful for post-hoc accounting:

from runcycles import EventCreateRequest, Subject, Action, Amount, Unit

response = client.create_event(EventCreateRequest(
    idempotency_key="evt-001",
    subject=Subject(tenant="acme"),
    action=Action(kind="api.call", name="geocode"),
    actual=Amount(unit=Unit.USD_MICROCENTS, amount=1_500),
))

Querying balances

At least one subject filter (tenant, workspace, app, workflow, agent, or toolset) is required:

response = client.get_balances(tenant="acme")
if response.is_success:
    print(response.body)

Response metadata

Every response exposes protocol headers for debugging and rate-limit awareness:

response = client.create_reservation(request)
print(response.request_id)            # X-Request-Id
print(response.rate_limit_remaining)   # X-RateLimit-Remaining (int or None)
print(response.rate_limit_reset)       # X-RateLimit-Reset (int or None)
print(response.cycles_tenant)          # X-Cycles-Tenant

Dry run (shadow mode)

Evaluate a reservation without persisting it. The @cycles decorator supports dry_run=True:

@cycles(estimate=1000, dry_run=True, client=client)
def shadow_func() -> str:
    return "result"

In dry-run mode, the server evaluates the reservation and returns a decision, but no budget is held or consumed. The decorated function does not execute — a DryRunResult is returned instead.

Overage policies

Control what happens when actual usage exceeds the estimate at commit time:

from runcycles import CommitOveragePolicy

# REJECT — commit fails if budget is insufficient for the overage
# ALLOW_IF_AVAILABLE (default) — commit succeeds if remaining budget covers the overage
# ALLOW_WITH_OVERDRAFT — commit always succeeds, may create debt

@cycles(estimate=1000, overage_policy="ALLOW_WITH_OVERDRAFT", client=client)
def overdraft_func() -> str:
    return "result"

Nested @cycles Calls

Calling a @cycles-decorated function from inside another @cycles-decorated function is allowed — it will not raise an error. However, each decorator creates an independent reservation that deducts budget separately:

@cycles(estimate=100, action_name="inner")
def inner_call():
    return "done"

@cycles(estimate=500, action_name="outer")
def outer_call():
    return inner_call()  # creates a SECOND reservation — 600 total deducted, not 500

This means nested decorators double-count budget. The outer reservation already covers the full estimated cost of the operation, so an inner reservation deducts additional budget from the same pool.

Recommended pattern: Place @cycles at the outermost entry point only. Inner functions should be plain functions without their own guard:

def inner_call():  # no @cycles — called within a guarded operation
    return "done"

@cycles(estimate=500, action_name="outer")
def outer_call():
    return inner_call()  # single reservation — 500 total

Features

• Decorator-based: @cycles wraps functions with automatic reserve/execute/commit lifecycle
• Programmatic client: Full control via CyclesClient / AsyncCyclesClient
• Sync + async: Both synchronous and asyncio-based APIs
• Automatic heartbeat: TTL extension at half-interval keeps reservations alive
• Commit retry: Failed commits are retried with exponential backoff
• Context access: get_cycles_context() provides reservation details inside guarded functions
• Typed exceptions: BudgetExceededError, OverdraftLimitExceededError, etc. for precise error handling
• Pydantic models: Typed request/response models with spec-enforced validation constraints
• Response metadata: Access request_id, rate_limit_remaining, and rate_limit_reset on every response
• Environment config: CyclesConfig.from_env() for 12-factor apps

Examples

The examples/ directory contains runnable integration examples:

Example	Description
basic_usage.py	Programmatic reserve → commit lifecycle
decorator_usage.py	@cycles decorator with estimates, caps, and metrics
async_usage.py	Async client and async decorator
openai_integration.py	Guard OpenAI chat completions with budget checks
anthropic_integration.py	Guard Anthropic messages with per-tool budget tracking
streaming_usage.py	Budget-managed streaming with token accumulation
fastapi_integration.py	FastAPI middleware, dependency injection, per-tenant budgets
langchain_integration.py	LangChain callback handler for budget-aware agents

See examples/README.md for setup instructions.

Development

pip install -e ".[dev]"

# Lint
ruff check .

# Type check (strict mode)
mypy runcycles

# Run tests with coverage (85% threshold enforced in CI)
pytest --cov runcycles --cov-fail-under=85

CI runs all three checks on Python 3.10 and 3.12 for every push and pull request.

Documentation

• Cycles Documentation — full docs site
• Python Quickstart — getting started guide
• Python Client Configuration Reference — all configuration options
• Error Handling Patterns in Python — handling budget errors

Requirements

• Python 3.10+
• httpx
• pydantic >= 2.0