Python free-threading support

[frankie567]

Now that free-threading (aka no-GIL) is a thing in Python 3.14, it could be interesting to explore if we can migrate to that. Not sure what kind of performance gain we could get, but it's worth to check.

The main blockers right now are libraries with C extensions that have not been adapted yet to this new mode.

Dependency blockers

1. sqlalchemy (ready, to release in 2.1): Implement support for free-threaded Python sqlalchemy/sqlalchemy#12881
   • but... asyncio features rely on greenlet, which doesn't seem to aim at supporting free-threading: Prevent greenlet from building on free-threaded Python python-greenlet/greenlet#423
2. asyncpg: Add Python 3.14 support, experimental subinterpreter/freethreading support MagicStack/asyncpg#1279
3. httptools (dependency of Uvicorn): Support for free-threaded Python MagicStack/httptools#118

Experiments

2025-10-18

Tried to run the API with:

• env PYTHON_GIL=0 to avoid greenlet warning
• Installed asyncpg from Add Python 3.14 support, experimental subinterpreter/freethreading support MagicStack/asyncpg#1279
• --http h11 option of Uvicorn to avoid 3

Server is starting, can serve a few requests, but then blocks and doesn't answer new requests. Probably a concurrency problem with greenlet.