[MuonChaser]

Overview

Fixes #63162: honor the tri-state return_tokens_as_token_ids override on both disaggregated derender paths, including generate streaming after merged #63103.

Claims

• Explicit request true/false overrides the answering server's flag; omitted/null falls back to that server's setting.
• /render omits the new context key when null, preserving legacy generate compatibility for default requests. Explicit overrides require an upgraded generate node.
• Full and streaming chat/completion logprobs retain their existing placeholder-byte, decoding and hidden-reasoning contracts; raw tokens and non-derender text behavior remain unchanged.

Validation

Check	Result
Six new streaming cases with main's serving implementation, keeping the new context field constant	2 failed / 4 passed before the tokenizer fix; all 6 pass after
Incorrect text-only text_mode merge negative control	All 6 fail with an error stream
Focused protocol, conversion and generation-stream suites, including new cases	120 passed in 44.77s
Full/stream derender routes and render omission cases over HTTP	34 passed in 82.14s
Contributed real-model test using the existing indirect server/client fixtures, Qwen3-0.6B	2 passed in 102.39s
Additional real-model streaming parity probe, both server flags and all request values	2 passed in 77.93s
All applicable pre-commit hooks, including mypy and Buildkite tethering	Passed

The Rust frontend capability check skips the two unsupported render cases. No Rust server E2E, model-quality evaluation or performance benchmark is claimed. Existing entrypoints integration CI selects the changed suites; upstream CI has not run because the contributor pre-run gate remains unsatisfied.

Reproduction commands and before/after output

.venv/bin/python -m pytest \
  tests/entrypoints/scale_out/token_in_token_out/test_generate_stream.py \
  tests/entrypoints/scale_out/derender/test_generate_logprobs_conversion.py \
  tests/entrypoints/scale_out/token_in_token_out/test_protocol.py \
  tests/entrypoints/scale_out/token_in_token_out/test_tokens_logprobs.py -q
.venv/bin/python -m pytest \
  tests/entrypoints/scale_out/render/test_render.py \
  tests/entrypoints/scale_out/derender/test_derender.py \
  tests/entrypoints/scale_out/derender/test_derender_stream.py \
  -k 'logprob_override or test_render_omits_null_token_id_override' -q
.venv/bin/python -m pytest \
  tests/entrypoints/scale_out/token_in_token_out/test_serving_tokens.py \
  -k test_derender_logprob_request_override -q
.venv/bin/python -m pre_commit run

For the isolated streaming regression, keep the new tests/protocol field and substitute main 3b6eeb0606's serving.py, then run:

.venv/bin/python -m pytest \
  tests/entrypoints/scale_out/token_in_token_out/test_generate_stream.py \
  -k test_stream_derender_logprob_request_override -q

Before:

E AssertionError: assert ('token_id:10', None) == ('é', [195, 169])
2 failed, 4 passed, 60 deselected, 1 warning in 3.49s

After restoring the fix:

6 passed, 60 deselected, 1 warning in 3.77s

GPU validation used the official CUDA wheel for 7ff608a03c (merged #63103), with the six patched Python modules overlaid and hash-matched to this rebased checkout. Serving/model Python paths are unchanged between that wheel base and the rebase base; unrelated newer Kimi kernel CMake pins were not rebuilt or validated. The Qwen checkpoint is revision c1899de289a04d12100db370d81485cdf75e47ca, tested on one RTX 4090 with eager execution, prefix caching disabled and 30% GPU memory utilization.

The human submitter confirmed line-by-line review of this rebased revision and personally running both the new streaming regression and the updated GPU fixture regression before publication.

Details

The request override was dropped at render serialization, generate used only its server flag, and separate derender always decoded. A nullable ParseContext field preserves explicit false; field-level null omission prevents adding an unknown key for older generate nodes. Each answering path resolves the override against its own server default. Placeholder formatting reuses the existing helper; decoded logprobs retain the existing decoder and UTF-8 fallback repair.

The rebase keeps main's streaming processor setup, _logprob_settings and text_mode behavior. The model regression reuses the module's indirect server fixture, avoiding a nested server while another fixture owns GPU memory. Its Rust capability skip matches the unsupported /render route.

Duplicate searches found only this PR and merged #60082/#63103; neither merged feature includes this request-override fix. The affected logprobs docs explain precedence and rolling upgrade behavior. AI assistance was used for implementation, tests, documentation and review preparation.

---

Pull Request Checklist

• I used vLLM's /pr-checklist skill. (Mandatory for agents, optional for humans).

• AI assistance was used during the creation of this PR.

• Design Fit: Minimizes impact on core components, reuses existing functionality, and justifies added complexity.

• Testing and Validation: Validates the change and ensures any added tests are meaningful and reliable, with CI coverage or documented CI resource constraints and validation performed outside CI.

• Code Quality and Style: Keeps code and comments clear and concise, and updates relevant documentation and examples.

• Pull Request Contents: Includes a brief summary and relevant links, supports claims with evidence, explains root causes and implementation trade-offs, and follows the contributing guide.

[claude]

Claude Code Review

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[mergify]

Documentation preview: https://vllm--63173.org.readthedocs.build/en/63173/

[DarkLight1337]

cc @hickeyma

[hickeyma]

Thanks @MuonChaser for pushing the fix. It looks good and covers everything in #63162. A few things to address:

• test_render_generate_logprob_override asserts that derender with stream=true returns a 400. #63103 removes that restriction, so this test breaks once that merges. It's not related to this bug anyway, so please drop it.
• There seems like a lot of tests compared to the fix. Can you move the coverage into the existing suites instead of adding a new file with its own tokenizer, engine and app?
  • _resolve_logprobs placeholders → test_generate_logprobs_conversion.py
  • /derender precedence → test_derender.py / test_derender_stream.py
  • _logprobs_tokenizer precedence → test_serving_tokens.py (_build_serving_tokens already takes the flag)
• Also drop the cases that pass whatever the flag is set to: the hidden reasoning ones, the missing parse_context check and the top-logprob count.
• Both tests change settings on the module scoped app fixture and the two derenderer references point at the same object. That only works because every test sets both values. Please use monkeypatch or a functionscoped fixture
• ParseContext.to_chat_request() now passes return_tokens_as_token_ids through but nothing reads it from there. Either drop it or have _logprobs_tokenizer read it from derender_request so there's one place to look.
• In _resolve_logprobs the not return_tokens_as_token_ids and checks before the U+FFFD repair can't trigger because a token_id:N string never ends in U+FFFD. You can remove them.
• self._return_tokens_as_token_ids(...) gets called for every choice. Work it out once next to top_limit. That'll also shorten the five call sites.
• Placeholder bytes come back as null on both derender paths. Coupled chat returns bytes there, though it's not consistent about it either. I'm fine with null since that matches generate's text mode but please add a comment in the parity test saying why the coupled bytes get blanked out. Right now it looks like the test is just hiding the difference.

[MuonChaser]

@hickeyma Addressed in 08b40a0.

Thanks for the detailed review. I removed the standalone route-test application and reused the existing conversion, derender and streaming suites. The real-model request-override regression now lives in test_serving_tokens.py, with a comment explaining the existing coupled/derender placeholder-bytes difference. The unrelated streaming rejection, hidden-reasoning, missing-context and top-count checks are gone; server defaults are passed through parametrized server fixtures without shared-state mutation.

I also removed the unused to_chat_request() propagation and redundant U+FFFD guards, and resolve the flag once per call beside top_limit on all five derender paths.

Validation: five representative new HTTP cases fail on the baseline for decoded-versus-placeholder mismatches; all 30 revised HTTP cases pass with the fix. The existing focused suites pass 101 tests, the real-model regression passes both server configurations, and staged pre-commit checks pass.

[hickeyma]

Thanks @MuonChaser, LGTM.

A few optional follow ups, none of them blocking:

• The new test in test_serving_tokens.py starts its own server for each flag value. The module server fixture already takes indirect params, so it could reuse that and cut most of the extra args. (My earlier pointer to _build_serving_tokens was wrong, sorry about that. That helper is in test_generate_stream.py.)
• /render now always sends return_tokens_as_token_ids in parse_context, even when it's null. That means an older generate node rejects every derender request, not just the ones that set it. The docs cover upgrade order but leaving the field out when it's None would avoid the problem.
• The streaming override test starts 6 render servers. Chat and completion could share one per flag value.

[DarkLight1337]

@claude review

[claude]

🔴 During a render-first rolling upgrade, every output_mode: "derender" request fails with a 400 on older generate nodes, including requests that never set the flag. The new return_tokens_as_token_ids field defaults to None, but /render always serializes it. Older nodes reject any unknown parse_context key in derender mode, including a null value. Fix: omit the field from the /render output when it is None, for example by building ParseContext with only the explicitly set value. Only requests that actually set the override should then need an upgraded generate node.

Why this was flagged

ServingRender._build_parse_context (vllm/entrypoints/scale_out/render/serving.py:236) always sets return_tokens_as_token_ids=request.return_tokens_as_token_ids, which is usually None. The /render routes return the whole GenerateRequest through create_json_response (render/api_router.py:50, :71), so "return_tokens_as_token_ids": null appears in every parse_context. Older generate nodes parse ParseContext with extra="allow". Their _check_parse_context_fields (protocol.py:403) then fails any derender request that has an unknown key. As a result, every derender request routed from an upgraded render node to an older generate node gets a 400, not just ones that use the new override. On the base branch the field is absent and these requests succeed. The doc note in token_in_token_out.md says to upgrade generate nodes first and calls this accepted. It still means a render-first or mixed rollout breaks all derender traffic, and omitting the field when it is null would avoid that cost.

Verification: Trigger: render nodes are upgraded before generate nodes, and clients send output_mode: "derender". render/serving.py:236 always sets return_tokens_as_token_ids, so every parse_context carries "return_tokens_as_token_ids": null. _check_parse_context_fields (base protocol.py:402-411) raises, and that becomes a 400. Before this change those requests worked.

[MuonChaser]

Addressed in 4084e72.

Fixed by omitting only None at the ParseContext field's serialization boundary. Missing/null request values no longer add a key to /render responses; explicit false and true remain serialized and retain their precedence.

The new live render-server regression fails for the two default cases before the change and passes all four cases after it. I also checked the actual HTTP payloads against the generate protocol from b689feb: default requests are accepted, while explicit overrides still fail closed in derender mode. The broader routes (34 tests), focused suites (101 tests), real-model regression (2 tests) and staged pre-commit checks pass. Updated the rollout documentation accordingly.

[mergify]

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @MuonChaser.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork

[hickeyma]

@MuonChaser #63103 merged and this needs a rebase. Some things to be handled also:

• In serving.py, keep main's side and just pass request to _logprobs_tokenizer. The PR's text_mode line breaks streaming derender logprobs.
• test_derender_logprob_request_override needs the Rust frontend skip because /render returns 501 there. It should also use the indirect server param becaue a second server will probably fail the free memory check while the module server holds the GPU. I said this was optional last time but it's required now.
• Please add a mock test in test_generate_stream.py for the override with stream: true.

[MuonChaser]

@hickeyma Addressed in a0e3dde; rebased with #63103 included.

I kept main's streaming setup and _logprob_settings unchanged, including treating derender as text mode, and only passed the request into the tokenizer selector.

The model regression now uses the existing indirect module server/client fixtures with Qwen3-0.6B, plus the Rust frontend capability skip. Added six scripted-engine streaming override cases to test_generate_stream.py. With main's serving implementation and the context field held constant, the two explicit override cases fail; all six pass with the fix. The incorrect text-only merge also makes all six cases fail.

Validation: 120 focused tests, 34 HTTP cases, both contributed real-model fixture cases, two additional real-model streaming parity cases, and all applicable pre-commit checks pass. The Rust selection check skips the two unsupported cases; no Rust E2E is claimed.

[hickeyma]

Thanks @MuonChaser nearly there. One more change:

test_derender_logprob_request_override compares logprobs with == across separate requests. Exact floats could make this flaky. The server fixture's comment already mentions 1 ULP differences on ROCm and test_derender_parity.py only compares token and bytes. Please compare token and bytes exactly and use pytest.approx for logprob.

[MuonChaser]

@hickeyma Addressed in 638fbfd. Sampled and top-candidate logprob values now use pytest.approx; token strings, bytes and the rest of the response structure still compare exactly.

Validated the actual test coroutine with one-ULP differences and negative token/bytes/logprob mutations; six streaming cases and applicable pre-commit checks pass. This revision only changes test assertions; no new GPU run is claimed.

[hickeyma]

Thanks @MuonChaser for the update. One last thing. The default pytest.approx tolerance is too tight here. With a bf16 model, a one step logit change moves the logprob by much more than 1e-6 relative and near certain tokens round to steps of about 1.2e-7. The default abs=1e-12 won't absorb this. Do you mind using pytest.approx(x, abs=1e-3) as test_vision.py does?

[MuonChaser]

@hickeyma Addressed in 9ca8dcf. Both sampled and top-candidate logprobs now use pytest.approx(..., abs=1e-3), matching test_vision.py; token strings, bytes and response structure remain exact.

Offline assertion checks accept bf16-logit and near-zero differences while still rejecting incorrect tokens/bytes and out-of-tolerance logprobs. Applicable pre-commit checks pass.