Compatibility

Spec version 0.1.0. OpenFeature specification floor v0.8.0. Source: SDK master dfeb478 plus live registry checks on 2026-08-17.

Language surfaces are not identical. This page records the asymmetry. Do not assume a method exists in every SDK.

Packages and publish state

Surface	Package	Version in tree	Published? (verified 2026-08-17)
Node / Bun / Deno	`@fireweaveai/sdk`	`2.1.0`	Yes. npm `0.1.0`, `2.0.0`, `2.1.0`. Dist-tag `latest` = 2.1.0. `2.0.0` is a different API (direct PostHog adapter). Pin `2.1.0`.
Python	`fireweave`	`0.1.0`	Yes on PyPI (`fireweave==0.1.0`). `pip install 'fireweave[openfeature]'` is valid. Checkout remains an alternative for an unreleased tree.
Go	`github.com/FireWeave-HQ/fireweave-sdk/sdks/go`	`0.1.0` (matrix); `go.mod` is `go 1.25.12`	No. Go proxy 404. Checkout + `replace` only.
Java	`ai.fireweave:fireweave-{sdk,openfeature,adapter-posthog,testing}`	`0.1.0-SNAPSHOT`	No. POM: “DO NOT PUBLISH.” Maven Central has no `ai.fireweave` artifacts.
Browser	`@fireweaveai/web-sdk`	`2.1.0`	Yes on npm (`2.1.0`, `gitHead` = `dfeb478`). `npm install @fireweaveai/web-sdk@2.1.0` is valid.

Registry tags can move. Re-check npm/PyPI before you ship install copy. As of 2026-08-17: Node latest = 2.1.0, Web 2.1.0, Python 0.1.0; Go and Java stay unpublished.

License MIT; “do not redistribute packages built from this repository until the license is ratified and publication is authorized.”

Runtime floors (manifests)

CI also runs extra cells (latest / stable / canary). Those float. Support floors are the manifest numbers, not the floating cells.

SDK	Manifest floor	Also exercised in CI (not a guarantee)
Node	Node `>=20.20` (`engines`)	Node 20 + 24
Bun (same package)	Bun `1.2` (runtime docs)	Bun 1.2.0 + latest
Deno (same package)	Deno `2.0` (runtime docs)	`v2.x` + canary
Python	Python `>=3.10` (`requires-python`)	3.10 + 3.14
Go	`go 1.25.12` (`go.mod`)	`1.25.x` + stable
Java	Java 11+ (`maven.compiler.release`)	JDK 11 + 25
Web	Browser. No Node/Deno target.	Bun + happy-dom only

Evaluation types

OpenFeature and the wire use flagKey. Native product noun is control point where that namespace exists.

	Native evaluate	Boolean	String	Numeric	Object
Node 2.1	`client.controlPoints.*` (`flags` alias)	`getBooleanValue`	`getStringValue`	`number` (IEEE-754 double)	`getObjectValue`
Python	`client.control_points.*` (`flags` alias)	`get_boolean_value`	`get_string_value`	`integer` + `float`	`get_object_value`
Go	`client.Flags().Evaluate` only	via `FlagTypeBoolean`	via `FlagTypeString`	`integer` + `float`	via `FlagTypeObject`
Java	`evaluate` / `getBooleanValue` / `getStringValue`	helper	helper	`INTEGER` / `FLOAT` via `evaluate` or OF	via `evaluate` or OF
Web	`client.controlPoints.` (sync*)	`getBooleanValue`	`getStringValue`	`number`	`getObjectValue`

Numeric limitations (pre-declared)

Language	Limitation	Behavior
Node / Web	Single `number` resolver; IEEE-754 double	Integers beyond ±(2^53−1) are not lossless. Node: 2 conformance skips.
Java OpenFeature	Integer resolver is 32-bit `Integer`	Outside range → `TYPE_MISMATCH` + default (never silent truncation). 1 skip.
All	Canonical JSON numbers	Cross-language integer reliability within ±(2^53−1).

Go OpenFeature integers are int64.

Feature matrix

Capability	Node 2.1	Python	Go	Java	Web
Product namespace	`controlPoints` (`flags` alias)	`control_points` (`flags` alias)	`Flags()` only	none	`controlPoints` (sync)
`registerTarget` / identify	`runtime.registerTarget`	`runtime.register_target`	absent	absent	`client.identify()` → `registerTarget`
Remote adapter	`FireweaveRemoteAdapter`	`FireweaveRemoteAdapter`	`adapters/remote`	`FireweaveRemoteAdapter`	`FireweaveRemoteWebAdapter`
In-memory	`InMemoryAdapter`	`InMemoryAdapter`	`adapters/inmemory`	`ai.fireweave.testing.InMemoryAdapter`	`InMemoryWebAdapter`
Local / dev adapter	`FireweaveLocalAdapter`	`FireweaveLocalAdapter`	absent	absent	`FireweaveLocalWebAdapter`
Direct PostHog adapter	removed	`fireweave[posthog]`	`adapters/posthog`	seam only (`create(config)` → `UnsupportedCapability`)	none
In-process local eval	none	via PostHog extra	via PostHog adapter	blocked on unpublished `com.posthog:posthog-server`	never (`localEvaluation` structurally false)
Env-var config	`FW_API_URL`, `FW_PROJECT_API_KEY`, `FW_DEPRECATION_WARNINGS`	same on remote adapter	`FW_API_URL`, `FW_PROJECT_API_KEY` on remote	no `System.getenv`	reads no environment
Default host allowlist	Fireweave hosts + loopback	PostHog hosts + loopback	PostHog (PostHog adapter) / configured host + loopback (remote)	PostHog hosts + loopback	Fireweave hosts + loopback
`sendExposure` default	false	false	false	false	false
Shutdown flushes exposures	yes	yes	via `Flush` / provider shutdown	`close()` does not	yes (+ unload flush)
Guardrails	stub	stub	stub	stub	stub
OpenFeature Tracking (§6)	not implemented	not implemented	not implemented	not implemented	not implemented

OpenFeature pins

Binding	Provider	OF SDK pin	Resolvers
Node	`FireweaveProvider`	`@openfeature/server-sdk` ^1.22.0 (peer)	boolean, string, number, object
Python	`fireweave.openfeature.FireweaveProvider`	`openfeature-sdk` `>=0.10,<0.11` extra	boolean, string, integer, float, object
Go	`openfeature.NewProvider`	`go-sdk` v1.17.2	boolean, string, float, int64, object
Java	`ai.fireweave.openfeature.FireweaveProvider`	`dev.openfeature:sdk` 1.15.1	boolean, string, 32-bit Integer, double, object
Web	`FireweaveWebProvider`	`@openfeature/web-sdk` ^1.9.0 (peer)	boolean, string, number, object — sync

Verified: typed resolvers, detailed resolution, flagMetadata, provider initialize/shutdown, user-registered hooks. FireWeave ships no product hooks except Go’s reserved-key guard. Domains are domain-safe. Multi-provider: compatible where OpenFeature ships it (Node); untested on Python. Tracking: planned, not present. See OpenFeature.

Conformance

From docs/compatibility.md + contracts/README.md:

	Fixtures
Server contracts (65)	Python 65/65, Go 65/65, Java 64/65, Node 63/65
Web (`contracts/web/`)	10/10

All skips are pre-declared (skipped-with-documented-limitation). Node skips are the IEEE-754 integer fixtures. Java skip is the 32-bit integer range fixture.

Server vs web

	Server SDKs	Web
`controlPoints.*`	Promise / blocking	synchronous
Evaluation source	per-call (Node remote has no cache)	prefetched cache
Extra lifecycle	—	STALE (5s prefetch ceiling)
Telemetry flush	shutdown hook (except Java `close`)	`visibilitychange` / `pagehide`, `keepalive` / `sendBeacon`
Config	env where implemented	constructor only

Known gaps (do not paper over)

Java PostHog — PostHogAdapter.create(config) → UnsupportedCapability until upstream publishes a Java server SDK.
Release/signal delivery skew — Go (and Java via the adapter seam) deliver release transitions/signals to the backend telemetry sink; Node/Python may record some paths in-process only. NEEDS VERIFICATION per adapter before claiming “signals always reach fw-server.”
OpenFeature Tracking (§6) — not implemented. Default evaluate remains side-effect-free (sendExposure false).

Language pages

Node.js, Bun, Deno

@fireweaveai/sdk 2.1.0 vs 2.0.0.

Python

fireweave extras and snake_case.

Go

Flags() only; no registerTarget.

Java

No env auto-read; close does not flush.

Browser

Sync reads, identify, STALE.

Get Started

SDKs

Concepts

OpenFeature

Production

Testing

Troubleshooting

Migration

Reference

Packages and publish state

Runtime floors (manifests)

Evaluation types

Numeric limitations (pre-declared)

Feature matrix

OpenFeature pins

Conformance

Server vs web

Known gaps (do not paper over)

Language pages

Node.js, Bun, Deno

Python

Go

Java

Browser

​Packages and publish state

​Runtime floors (manifests)

​Evaluation types

​Numeric limitations (pre-declared)

​Feature matrix

​OpenFeature pins

​Conformance

​Server vs web

​Known gaps (do not paper over)

​Language pages

Node.js, Bun, Deno

Python

Go

Java

Browser

Packages and publish state

Runtime floors (manifests)

Evaluation types

Numeric limitations (pre-declared)

Feature matrix

OpenFeature pins

Conformance

Server vs web

Known gaps (do not paper over)

Language pages