vLLM nightly (0.20.2rc1.dev9+) emits the qwen3 reasoning parser's output
under `delta.reasoning` (legacy field name), not `delta.reasoning_content`
that soak-helper.py was watching. Result: for any thinking-on response
whose `<think>` block doesn't close within `max_tokens`, soak-helper saw
zero deltas → fell back to the "couldn't measure" path → reported
`ttft_ms == t_ms` and `decode_tps = 0.0`. The model was generating
correctly; the harness just couldn't see the wire output.
Repro request (JDWarner's #107 turn 5): math problem with
`max_tokens=2000` + `chat_template_kwargs.enable_thinking=true`.
Before patch:
status=200 t_ms=22709 ttft_ms=22709 decode_tps=0.0
completion_tokens=2000 content="" reasoning_content=""
After patch (same request, same compose, same model):
status=200 t_ms=22709 ttft_ms=234 decode_tps=88.985
completion_tokens=2000 content="" reasoning_content="Here's a thinking
process:\n\n1. **Understand the User's Problem:**\n..." (3959 chars)
Validation soak (fresh-mode, 20 sessions × 5 turns = 100 turns, qwen3.6-27b
dual.yml):
verdict PASS
silent_empty 0 / 100 (0.0%) ← was ~3-5/40 baseline
p50_decode_tps 90.22
p95_ttft_ms 1389
errors 0
max_growth 0 MiB / 200
Closes the cross-rig "silent-empty turn-5" pattern parked behind the
Cliff 2b investigation — it was a harness measurement bug, not a model
or rig issue.
noonghunna
88eb67aa18