FastAPI `Depends(func, scope="function")` with `yield`

The Fix

pip install fastapi==0.128.4

Based on closed fastapi/fastapi issue #14316 · PR/commit linked

Production note: This usually shows up under retries/timeouts. Treat it as a side-effect risk until you can verify behavior with a canary + real traffic.

Jump to Verify Open PR/Commit

@@ -129,7 +129,10 @@ def get_parameterless_sub_dependant(*, depends: params.Depends, path: str) -> De
         use_security_scopes.extend(depends.scopes)
     return get_dependant(
-        path=path, call=depends.dependency, security_scopes=use_security_scopes
+        path=path,
+        call=depends.dependency,

repro.py

from types import NoneType
from typing import Iterator, Annotated

from fastapi import APIRouter
from fastapi import Depends
from fastapi import FastAPI


app = FastAPI()


class ApplicationError(Exception): ...


def dependency_with_cleanup_error() -> Iterator[None]:
    yield
    raise ApplicationError()


router = APIRouter(
    dependencies=[Depends(dependency_with_cleanup_error, scope="function")]
)


@router.get("/broken")
def broken():
    # Will return 200, and then fail in the cleanup.
    return {"status": "ok"}


@router.get("/works")
def endpoint(
    v: Annotated[NoneType, Depends(dependency_with_cleanup_error, scope="function")],
):
    # Will correctly return 500
    return {"status": "ok"}


app.include_router(router)

verify

Re-run the minimal reproduction on your broken version, then apply the fix and re-run.

fix.md

Option A — Upgrade to fixed release\npip install fastapi==0.128.4\nWhen NOT to use: Do not use this fix if you rely on the previous cleanup behavior of dependencies.\n\n

Why This Fix Works in Production

Trigger: `Depends(func, scope="function")` with `yield` dependency exits after the request is sent instead of after the function
Mechanism: Function-scoped dependencies were not cleaned up correctly after the response was sent
Why the fix works: Enables proper support for `scope="function"` on `APIRoute` dependencies by passing the dependency’s scope through to `get_dependant`. (first fixed release: 0.128.4).

Why This Breaks in Prod

Function-scoped dependencies were not cleaned up correctly after the response was sent
Production symptom (often without a traceback): class ApplicationError(Exception): ...

Proof / Evidence

GitHub issue: #14316
Fix PR: https://github.com/fastapi/fastapi/pull/14301
First fixed release: 0.128.4
Reproduced locally: No (not executed)
Last verified: 2026-02-08
Confidence: 0.85
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.53

Discussion

High-signal excerpts from the issue thread (symptoms, repros, edge-cases).

Jump to Sources Open on GitHub

“This was solved by https://github.com/fastapi/fastapi/pull/14301, released in FastAPI 0.121.1. 🐛”

@tiangolo · 2025-11-08 · confirmation · source

Failure Signature (Search String)

`Depends(func, scope="function")` with `yield` dependency exits after the request is sent instead of after the function

Copy-friendly signature

signature.txt

Failure Signature
-----------------
class ApplicationError(Exception): ...
def dependency_with_cleanup_error() -> Iterator[None]:

Error Message

Signature-only (no traceback captured)

error.txt

Error Message
-------------
class ApplicationError(Exception): ...
def dependency_with_cleanup_error() -> Iterator[None]:

Minimal Reproduction

repro.py

from types import NoneType
from typing import Iterator, Annotated

from fastapi import APIRouter
from fastapi import Depends
from fastapi import FastAPI


app = FastAPI()


class ApplicationError(Exception): ...


def dependency_with_cleanup_error() -> Iterator[None]:
    yield
    raise ApplicationError()


router = APIRouter(
    dependencies=[Depends(dependency_with_cleanup_error, scope="function")]
)


@router.get("/broken")
def broken():
    # Will return 200, and then fail in the cleanup.
    return {"status": "ok"}


@router.get("/works")
def endpoint(
    v: Annotated[NoneType, Depends(dependency_with_cleanup_error, scope="function")],
):
    # Will correctly return 500
    return {"status": "ok"}


app.include_router(router)

What Broke

Users experienced unexpected behavior with function-scoped dependencies in FastAPI routes.

Why It Broke

Function-scoped dependencies were not cleaned up correctly after the response was sent

Fix Options (Details)

Option A — Upgrade to fixed release Safe default (recommended)

pip install fastapi==0.128.4

When NOT to use: Do not use this fix if you rely on the previous cleanup behavior of dependencies.

Use when you can deploy the upstream fix. It is usually lower-risk than long-lived workarounds.

Fix reference: https://github.com/fastapi/fastapi/pull/14301

First fixed release: 0.128.4

Last verified: 2026-02-08. Validate in your environment.

When NOT to Use This Fix

Do not use this fix if you rely on the previous cleanup behavior of dependencies.

Verify Fix

verify

Re-run the minimal reproduction on your broken version, then apply the fix and re-run.

Did This Fix Work in Your Case?

Quick signal helps us prioritize which fixes to verify and improve.

Prevention

Capture the exact failing error string in logs and tests so you can reproduce via a minimal script.
Pin production dependencies and upgrade only with a reproducible test that hits the failing path.

Version Compatibility Table

Version	Status
0.128.4	Fixed

Related Issues

No related fixes found.

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Related clusters: Configuration error Data consistency Race condition

Sources

We don’t republish the full GitHub discussion text. Use the links above for context.

FastAPI `Depends(func, scope="function")` with `yield` dependency exits after the request is sent (Fix)