Gemma-4-31B-it occasionally emits <turn|> token when served via vLLM, causing failures when using it with GitHub Copilot Custom Model Provider

#138
by aygupt - opened

I have been using gemma-4-31B-it deployed with vLLM in Github CoPilot mainly for coding purposes. However sometimes I get this error after getting a response back for a prompt :-

...<turn|>

x Sorry, no response was returned.

Is this an issue with chat-template or an issue from vLLM's side ?

I have attached a screenshot for more details.
chat_error

My Configuration :-
Model: google/gemma-4-31B-it
Serving: vLLM
Client: GitHub Copilot (Custom Model Provider)
Deployment: Docker
vLLM: 0.25.1

vLLM Configuration :-
--model google/gemma-4-31B-it
--served-model-name personal-coder
--dtype auto
--kv-cache-dtype fp8
--max-model-len 143360
--override-generation-config '{"temperature":1.0,"top_p":0.95,"top_k":64}'
--max-num-batched-tokens 5120
--gpu-memory-utilization 0.97
--enable-prefix-caching
--enable-chunked-prefill
--enable-auto-tool-choice
--tool-call-parser gemma4
--reasoning-parser gemma4
--trust-remote-code
--language-model-only

Google org

Hi @aygupt , thanks for reporting this . I'd like to try reproducing this on my end.
Could you please share the minimal reproducible prompt or message payload that reliably triggers this error? Also, just a quick check there was an recent update to the Gemma 4 chat template that touches on turn boundaries. Could you confirm if you're using the latest chat template ?

Sign up or log in to comment