[Bugfix] Fixed when return_token_ids=False, the first event still contains prompt_token_ids.

[chaunceyjiang]

Purpose

Follow up #22587

FIX #27336

vllm/vllm/entrypoints/openai/protocol.py

Lines 1241 to 1250 in 3567816

	return_token_ids: bool | None = Field(
	default=None,
	description=(
	"If specified, the result will include token IDs alongside the "
	"generated text. In streaming mode, prompt_token_ids is included "
	"only in the first chunk, and token_ids contains the delta tokens "
	"for each chunk. This is useful for debugging or when you "
	"need to map generated text back to input tokens."
	),
	)

Test Plan

echo
curl http://localhost:8000/v1/completions \
-H "Content-Type: application/json" \
-H "Authorization: Bearer YOUR_API_KEY" \
-d '{
    "prompt": "Once upon a time, there was a brave knight named",
    "stream": true,
    "temperature": 0.7
}'

main:

data: {"id":"cmpl-bb3c414e6a24489c8a25bd07b6c86394","object":"text_completion","created":1761553425,"model":"/home/jovyan/qwen3-8b","choices":[{"index":0,"text":" Sir","logprobs":null,"finish_reason":null,"stop_reason":null,"prompt_token_ids":[12522,5193,264,882,11,1052,572,264,33200,46609,6941],"token_ids":null}],"usage":null}

this pr:

data: {"id":"cmpl-d1eb817714c94cb2b5fb559b5d2fd7fa","object":"text_completion","created":1761553358,"model":"/home/jovyan/qwen3-8b","choices":[{"index":0,"text":" Sir","logprobs":null,"finish_reason":null,"stop_reason":null,"prompt_token_ids":null,"token_ids":null}],"usage":null}

Test Result

---

Essential Elements of an Effective PR Description Checklist

• The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
• The test plan, such as providing test command.
• The test results, such as pasting the results comparison before and after, or e2e results
• (Optional) The necessary documentation update, such as updating supported_models.md and examples for a new model.
• (Optional) Release notes update. If your change is user facing, please update the release notes draft in the Google Doc.

[chaunceyjiang]

/cc @ultmaster PTAL.

[chaunceyjiang]

Follow up #22587

/cc @njhill @youkaichao @DarkLight1337 PTAL.

[DarkLight1337]

Fixed when return_token_ids=True

You mean when return_token_ids=False?

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

ℹ️ About Codex in GitHub

Codex has been enabled to automatically review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

When you sign up for Codex through ChatGPT, Codex can also answer questions or update the PR, like "@codex address that feedback".

[chaunceyjiang]

You mean when return_token_ids=False?

ohh, yes. thanks~

[DarkLight1337]

Thanks for fixing!

[ultmaster]

I've looked at the PR and it seems to be a bug introduced by me. Sorry. The PR looks good.