Python

fireweave is the FireWeave server SDK for Python. It evaluates control points, optionally registers targets, drives a release lifecycle, and records exposures and signals. OpenFeature and the wire protocol still use the parameter name flagKey.

FireWeave is pre-release. Core has zero runtime dependencies. OpenFeature and the PostHog adapter are extras.

Supported versions

From pyproject.toml:

	Value
Package	`fireweave` `0.1.0`
Python	`>=3.10`
Extra `fireweave[openfeature]`	`openfeature-sdk>=0.10.0,<0.11` (pre-1.0)
Extra `fireweave[posthog]`	`posthog==7.31.0`
Extra `fireweave[dev]`	both extras + pytest

Classifiers list 3.10–3.13. CI runs 3.10 and 3.14. Treat >=3.10 as the supported floor; do not treat floating CI cells as a support guarantee.

Install

PyPI has fireweave==0.1.0 (verified 2026-08-17). pip install 'fireweave[openfeature]' is valid. Checkout remains an alternative for a specific commit or an unreleased tree.

PyPI 0.1.0
From checkout

Verified 2026-08-17: PyPI fireweave 0.1.0, requires Python >=3.10, homepage FireWeave-HQ/fireweave-sdk.

pip install 'fireweave[openfeature]'
# optional: pip install 'fireweave[posthog]'

Re-check the index if you need extras or a newer tree than 0.1.0.

From docs/quickstart.md:

git clone https://github.com/FireWeave-HQ/fireweave-sdk && cd fireweave-sdk
python -m venv .venv
.venv/bin/pip install -e 'sdks/python[openfeature]'

Add ,posthog for the PostHog adapter. From sdks/python/: pip install -e '.[dev]'.

FIREWEAVE_POSTHOG_KEY and FIREWEAVE_POSTHOG_HOST appear in examples/python/ only. They are not SDK configuration. Remote-adapter env vars are FW_API_URL and FW_PROJECT_API_KEY.

Initialize

Construct the adapter and runtime explicitly. No hidden globals.

from fireweave import FireweaveClient, FireweaveRuntime, InMemoryAdapter

adapter = InMemoryAdapter({
    "new-checkout": {"type": "boolean", "enabled": True, "variant": "on", "value": True},
})
runtime = FireweaveRuntime(adapter)
runtime.initialize()
client = FireweaveClient(runtime)

assert client.control_points.get_boolean_value("new-checkout", False) is True
client.shutdown()

FireweaveClient is also a context manager: with FireweaveClient(runtime) as client:. initialize(backend_required=False). shutdown(timeout_ms=None) flushes exposures, then closes the adapter; never raises; idempotent. Default shutdown timeout: 10_000 ms. Async: from fireweave.aio import AsyncFireweaveClient — not in the core __all__. Wrappers offload via asyncio.to_thread.

Configuration and authentication

FireweaveConfig fields: project_api_key, host, personal_api_key, secret_key, local_evaluation, only_evaluate_locally, require_targeting_key, allow_anonymous, allowed_hosts, reserved_attribute_keys, limits, feature_flags_request_timeout_ms (default 3000), shutdown_timeout_ms (default 10000). FireweaveRemoteAdapter reads FW_API_URL and FW_PROJECT_API_KEY when options are omitted. Auth: Authorization: Bearer <key>. FW_DEPRECATION_WARNINGS=1 emits a one-shot notice when you use client.flags. Default DEFAULT_ALLOWED_HOSTS: five PostHog hosts (app.posthog.com, us.posthog.com, eu.posthog.com, us.i.posthog.com, eu.i.posthog.com) plus loopback. https off-loopback; http on loopback only. A literal "*" disables host pinning.

from fireweave import FireweaveRemoteAdapter, FireweaveRuntime

adapter = FireweaveRemoteAdapter()  # reads FW_API_URL + FW_PROJECT_API_KEY
runtime = FireweaveRuntime(adapter)
runtime.initialize()

See Configuration and auth.

Targets

from fireweave import RegisterTargetOptions

result = runtime.register_target(
    "user_42",
    RegisterTargetOptions(kind="user", properties={"plan": "pro", "region": "eu-west"}),
)
print(result.ok, result.error)

RegisterTargetOptions: kind, properties, environment. The remote adapter posts POST /v1/targets/register, retries once on retryable failures, and returns ok=False rather than raising. In-memory and local adapters report UnsupportedCapability. See Targeting and targets.

Control points

client.control_points is the product API. client.flags is the same object (deprecated alias). FlagType: BOOLEAN, STRING, INTEGER, FLOAT, OBJECT.

from fireweave import EvaluationContext, FlagType

ctx = EvaluationContext(targeting_key="user_42", attributes={"tier": "gold"})

on = client.control_points.get_boolean_value("new-checkout", False, ctx)
theme = client.control_points.get_string_value("checkout-theme", "classic", ctx)
count = client.control_points.get_integer_value("max-items", 0, ctx)
ratio = client.control_points.get_float_value("discount", 0.0, ctx)

decision = client.control_points.evaluate(
    "new-checkout", FlagType.BOOLEAN, False, ctx,
    include_payload=False,
    send_exposure=False,
)
print(decision.value, decision.reason)

Also: get_object_value, get_details (alias of evaluate). Evaluation never raises. send_exposure defaults to false. See Control points.

Releases

Snake_case. set_context requires rollout_id and stamp_ids (stmp_ + 26 Crockford characters). Optional change_id (chg_ + 26).

fw = client
fw.releases.set_context(
    rollout_id="rollout_01HZX3",
    change_id="chg_01HZXEX0000000000000000001",
    stamp_ids=["stmp_01HZXEX0000000000000000001"],
)
fw.releases.start()
fw.releases.complete()
# or: fw.releases.fail(reason="...")

Whether release transitions always reach fw-server is NEEDS VERIFICATION (compatibility known gap: Node/Python may record some paths in-process only).

See Releases.

Exposures

client.exposures.record("user_42", "new-checkout", "on", True)
client.exposures.flush()

record(targeting_key, flag_key, variant=None, value=None, rollout_id=None). Dedup is on (targetingKey, flagKey, variant, value). send_exposure on evaluate defaults to false. shutdown() flushes first. See Exposures.

Signals

client.signals.record_health("checkout-service", "ok", rollout_id="rollout_01HZX3")
client.signals.record_error("checkout-service", error_kind="Timeout", message="upstream")
client.signals.record_metric("checkout.latency_ms", 42.0, unit="ms")
client.signals.record_outcome("checkout", "completed")

See Signals and outcomes.

Capabilities

caps = client.capabilities.get()

guardrails.check / guardrails.evaluate are stubs (UnsupportedCapability). See Capabilities.

Adapters

Adapter	Import	Use
`FireweaveRemoteAdapter`	`from fireweave import FireweaveRemoteAdapter`	Production fw-server
`InMemoryAdapter`	`from fireweave import InMemoryAdapter`	Tests / offline
`FireweaveLocalAdapter`	`from fireweave import FireweaveLocalAdapter`	Dev `dev_flags` boolean map
`PostHogAdapter`	`from fireweave.adapters.posthog import PostHogAdapter`	Extra `fireweave[posthog]`. Not in core `__init__`.

Local OpenFeature helper (requires the openfeature extra):

from fireweave.openfeature import (
    make_fireweave_local_provider,
    get_fw_local_captures,
    reset_fw_local_captures,
)

provider = make_fireweave_local_provider(dev_flags={"new-checkout": True})

In-process local evaluation via PostHog (secret_key / personal_api_key + local_evaluation) is available on the PostHog extra, not on the remote adapter. See Adapters.

OpenFeature

Not in core __init__. Requires fireweave[openfeature]:

from openfeature import api
from openfeature.evaluation_context import EvaluationContext
from fireweave import FireweaveRuntime, InMemoryAdapter
from fireweave.openfeature import FireweaveProvider

runtime = FireweaveRuntime(InMemoryAdapter({
    "new-checkout": {"type": "boolean", "enabled": True, "value": True, "variant": "on"},
}))
api.set_provider(FireweaveProvider(runtime))
of_client = api.get_client()

enabled = of_client.get_boolean_value(
    "new-checkout", False, EvaluationContext(targeting_key="user_42"))
print("new-checkout:", enabled)

api.shutdown()

Resolvers: resolve_boolean_details, resolve_string_details, resolve_integer_details, resolve_float_details, resolve_object_details. Ctor: backend_required=False, include_payload=False. Multi-provider is untested on Python. OpenFeature Tracking is not implemented. See OpenFeature.

Errors

ErrorKind has the same 15 PascalCase kinds. Concrete subclasses include NotReadyError, FlagNotFoundError, TypeMismatchError, InvalidContextError, TargetingKeyMissingError (subtype of InvalidContextError, OF code TARGETING_KEY_MISSING), AuthenticationError, AuthorizationError, RateLimitedError, TimeoutError_, NetworkError, BackendUnavailableError, MalformedResponseError, UnsupportedCapabilityError, ConfigurationError, AlreadyClosedError, InternalError. Evaluation never raises. See Errors.

Testing

InMemoryAdapter fixture fields used in tests: type, enabled, value, variant, optional matchAttribute. The repo test-server does not implement POST /v1/targets/register. See Testing.

Shutdown

client.shutdown()  # flushes exposures, closes adapter, never raises
api.shutdown()     # if you used OpenFeature

See Initialize, ready, shutdown.

Not in this SDK

A controlPoints camelCase namespace (Python is control_points).
Working guardrails.
OpenFeature Tracking.

Quickstart

Offline evaluate in every language.

Compatibility

Type split, adapters, and conformance.

Get Started

SDKs

Concepts

OpenFeature

Production

Testing

Troubleshooting

Migration

Reference

Supported versions

Install

Initialize

Configuration and authentication

Targets

Control points

Releases

Exposures

Signals

Capabilities

Adapters

OpenFeature

Errors

Testing

Shutdown

Not in this SDK

Next

Quickstart

Compatibility

​Supported versions

​Install

​Initialize

​Configuration and authentication

​Targets

​Control points

​Releases

​Exposures

​Signals

​Capabilities

​Adapters

​OpenFeature

​Errors

​Testing

​Shutdown

​Not in this SDK

​Next

Quickstart

Compatibility

Supported versions

Install

Initialize

Configuration and authentication

Targets

Control points

Releases

Exposures

Signals

Capabilities

Adapters

OpenFeature

Errors

Testing

Shutdown

Not in this SDK

Next