anyio.NoEventLoopError when serving static files on Python 3.14 (dup of #2767)

[chouhandarsh]

Describe the bug
Running a Chainlit app on Python 3.14 crashes on every request that serves a static file
(including the initial page load) with anyio.NoEventLoopError: Not currently running on any asynchronous event loop. Available async backends: asyncio, trio. The error originates
from starlette/responses.py calling anyio.to_thread.run_sync(os.stat, self.path).

To Reproduce

1. Create a fresh virtual environment with Python 3.14
2. pip install chainlit
3. chainlit run app.py
4. Open http://localhost:8000 in a browser
5. See repeated anyio.NoEventLoopError tracebacks in the terminal

Screenshots

**Desktop **

• OS: Linux Fedora
• Browser Chrome
• Python version : 3.14.6
  chainlit version: 2.11.0

Additional context
This looks like a duplicate of #2767 — same traceback and root cause. Downgrading to
Python 3.12/3.13 in a fresh venv works around it.

[dosubot]

Hi @chouhandarsh! I'm Dosu and I'm helping the Chainlit team.

You're correct that this is the same root cause as #2767. The issue has been thoroughly diagnosed in #2952 — nest_asyncio.apply() (called at import time in chainlit/cli/__init__.py) corrupts asyncio task registration on Python 3.14 because it uses the loop= keyword argument that was removed in 3.14. This causes asyncio.current_task() to return None, which makes anyio think there's no running event loop [1].

A fix is available in PR #2953 which removes nest_asyncio entirely, since the entry point (asyncio.run(start())) doesn't actually need re-entrant loop support [1].

In the meantime, downgrading to Python 3.12 or 3.13 is the correct workaround.

To reply, just mention @dosu.

---

Share context across your team and agents. Try Dosu.

[github-actions]

This issue is stale because it has been open for 14 days with no activity.

[github-actions]

This issue was closed because it has been inactive for 7 days since being marked as stale.