[Triage] gunicron with fastapi and asgi no trace output on error

[keros]

Type

Bug Report

Description

I'm new to gunicorn and not 100% sure if this is a bug or if I doing something wrong.
I run into (my own) programming error and triggered an exception.
I looked into the logs and found nothing except of the access logs.

My question here should it be like this?
I expected that gunicorn logs the exception to stdout/stderr in this case?

Steps to Reproduce (for bugs)

Setup environment:

mkdir /tmp/logger-test
cd /tmp/logger-test
python3 -m venv venv
source venv/bin/activate
pip install "gunicorn~=26.0.0" "fastapi~=0.138.0"

My test app (app.py):

from fastapi import FastAPI


app = FastAPI()


@app.get("/ping")
async def ping() -> dict[str, str]:
    mylist = [1, 2, 3]
    print(f"mylist[0]: {mylist[0]}")
    print(f"mylist[25]: {mylist[25]}")  # force exception here
    return {"message": "pong"}

Run it:

gunicorn -c gunicorn.py

Access test app:

curl http://127.0.0.1:8080/ping
Internal Server Error

Configuration

My gunicorn config (gunicorn.py):

wsgi_app = "app:app"

accesslog = "-"
errorlog = "-"
loglevel = "debug"
capture_output = True

# asgi worker for fastapi
worker_class = "asgi"
workers = 2
worker_connections = 1000
bind = "127.0.0.1:8080"
control_socket = "-"
timeout = 30
max_requests = 5000

Logs / Error Output

Output on gunicron shell:

...
[2026-06-26 15:32:05 +0200] [50770] [DEBUG] GET /ping
mylist[0]: 1
[2026-06-26 15:32:05 +0200] [50770] [DEBUG] Exception after response complete (client disconnected)
127.0.0.1 - - [26/Jun/2026:15:32:05 +0200] "GET /ping HTTP/1.1" 500 21 "-" "curl/7.88.1"

### Gunicorn Version

gunicorn 26.0.0

### Python Version

Python 3.11.2

### Worker Class

asgi (beta)

### Operating System

Debian 12

### Additional Context

_No response_

### Checklist

- [X] I have searched existing discussions and issues for duplicates
- [X] I have checked the documentation and FAQ