[MayorX500]

Purpose

Add per-session language and prompt support for Qwen3-ASR realtime WebSocket transcription, and clean the streamed ASR output contract.

This PR allows realtime STT clients to request a specific language via session.update.language using ISO-639-1 codes such as en, zh, ja, ko, de, fr, and es. Omitting language, sending null, or sending "" keeps auto-detection behavior.

It also surfaces language metadata in transcription.delta.language and transcription.done.language, while stripping Qwen3-ASR's internal realtime preamble such as language English<asr_text> from user-visible transcript text.

This is not duplicating existing work: the related ASR language/prompt work did not cover the realtime WebSocket output contract and Qwen3-ASR realtime preamble cleanup path.

Documentation and the realtime example client were updated. This PR was developed with AI assistance and manually reviewed/tested.

Test Plan

Run focused realtime unit tests:

.venv/bin/python -m pytest -p no:cacheprovider \
  tests/entrypoints/speech_to_text/realtime/test_realtime_protocol.py \
  tests/entrypoints/speech_to_text/realtime/test_qwen3_asr_realtime_prompt.py \
  tests/entrypoints/speech_to_text/realtime/test_qwen3_asr_realtime_output.py \
  -q

Compile-check realtime modules not fully covered by the focused unit tests:

.venv/bin/python -m py_compile \
  vllm/entrypoints/speech_to_text/realtime/connection.py \
  vllm/entrypoints/speech_to_text/realtime/serving.py \
  vllm/model_executor/models/voxtral_realtime.py

Run live Qwen3-ASR realtime integration tests on an A100 host against:

VLLM_ALLOW_LONG_MAX_MODEL_LEN=1 vllm serve Qwen/Qwen3-ASR-1.7B \
  --host 0.0.0.0 \
  --port 8000 \
  --hf-overrides '{"architectures":["Qwen3ASRRealtimeGeneration"]}' \
  --max-model-len 4096 \
  --max-num-seqs 64 \
  --max-num-batched-tokens 8192 \
  --gpu-memory-utilization 0.8 \
  --enforce-eager

Integration coverage includes:

• English audio with auto language detection.
• Chinese audio with forced zh.
• Chinese audio forced to en, proving language forcing overrides detection.
• Chinese audio forced to ja, ko, de, fr, and es.
• Prompt/hint behavior.
• Empty language and empty prompt edge cases.
• Invalid model/language/error handling.
• Commit-before-session-update validation.
• Concurrent realtime connections with different languages.
• Reconfiguration before commit, where the last valid session.update wins.
• Assertion that <asr_text> and Qwen internal language preambles never leak into deltas.

Test Result

Focused unit tests:

17 passed, 15 warnings in 0.29s

Compile check:

PY_COMPILE_OK

Live integration suite on CerebrasA100 / A100 40GB:

SUMMARY: 20 passed, 0 failed, 20 total

Key live integration confirmations:

• transcription.delta and transcription.done include the expected language value.
• Auto-detected English returns language="en".
• Auto-detected Chinese via empty language returns language="zh".
• Forced languages return the requested language code.
• Prompt hints are applied.
• Concurrent sessions keep independent language configuration.
• No <asr_text> marker or language <Name><asr_text> preamble leaked into streamed output.

[claude]

Claude Code Review

This pull request is from a fork — automated review is disabled. A repository maintainer can comment @claude review to run a one-time review.

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[mergify]

Documentation preview: https://vllm--47563.org.readthedocs.build/en/47563/

[nielsreijers]

Hi,

Just curious: why was this closed? As far as I can tell there's still no support for Qwen ASR for language hints on the realtime path, right? It would be nice to have it!

[tamerrkanak]

@nielsreijers FYI: #61031 adds language (and prompt) to the Qwen3-ASR realtime path via session.update, reusing the REST prompt builder. Testing or feedback is very welcome.