Django 6, Python 3.14, UV - Failed to run server

[subinabid]

Describe the bug
A newly built app on Django 6 pythin 3.14 failed to start the server after adding drf-spectacular. Please note that UV is used as package manager. Only the installation is done. Settings are not chaged.

uv add drf-spectacular
uv run python manage.py runserver

The server is failing with exit code 245

uv run python manage.py check

There's a segmentation fault while running check

To Reproduce
UV is used for package maangement
A django 6 app that works well in development

uv add drf-spectacular
uv run python manage.py runserver

Expected behavior
The django dev server should start

[Freyja-Folkvangr]

Additional Python 3.14 compatibility issue: _UnionGenericAlias deprecation

This might be related to the segfault reported above. In drf_spectacular/plumbing.py:1340, there's an isinstance() check using typing._UnionGenericAlias:

return isinstance(hint, (
    # includes _UnionGenericAlias
))

Python 3.14 deprecated _UnionGenericAlias (Python docs):

In Python 3.14, types.UnionType is now an alias for Union, and both Union[int, str] and int | str create instances of the same class.

The segfault could occur when this deprecated internal class is used in isinstance() checks, as Python 3.14 changed the internal implementation of Union types.

Evidence

Running schema generation emits multiple warnings before potential crash:

drf_spectacular/plumbing.py:1340: DeprecationWarning: '_UnionGenericAlias' is deprecated and slated for removal in Python 3.17
  return isinstance(hint, (

Recommended Fix

Replace _UnionGenericAlias checks with the stable API:

from typing import get_origin, Union

# Instead of isinstance(hint, _UnionGenericAlias):
if get_origin(hint) is Union:
    # handle union type

Environment

• Python 3.14.2
• drf-spectacular 0.29.0
• Django 5.2.7