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[Model] DiffusionGemma: honor logprob_token_ids on the converging step - #57417

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LucasWilkinson merged 1 commit into
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mmastrac:dgemma-logprob-token-ids
Sep 18, 2026
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LucasWilkinson merged 1 commit into
vllm-project:mainfrom
mmastrac:dgemma-logprob-token-ids

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Purpose

DiffusionGemma ignores logprob_token_ids. The logprobs it stashes on a request's converging step only go through the top-k path, so a request cannot ask for specific
token ids.

The diffusion sampler now keeps the same LogprobTokenIdsState the autoregressive sampler does and passes it to compute_topk_scores with a per-row slot mapping, so
every requested id gets its exact logprob at every canvas position. Top-k alone, ids alone, or both all work.

Split out of #57250.

Test plan

Hardware: 1 DGX Spark.


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  • (Optional) The necessary documentation update, such as updating supported_models.md and examples for a new model.

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LGTM, thanks for the fix!

@LucasWilkinson LucasWilkinson added the ready ONLY add when PR is ready to merge/full CI is needed label Sep 17, 2026
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/ci run

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✅ @mmastrac, CI is now available for this PR.

  • /ci run starts upstream CI; /amd-ci run starts AMD CI only.
  • Your branch must contain every commit currently on its upstream target branch. Merge or rebase onto the latest target branch, then rerun the command. Append --allow-stale to a run command to test an outdated branch at your own risk.
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  • /ci cancel cancels scheduled or running CI builds for this PR branch; /amd-ci cancel does the same for AMD CI only.

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✅ Triggered Buildkite CI #89708 for commit a6f1b01fb13c.

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LucasWilkinson enabled auto-merge (squash) September 17, 2026 21:09
auto-merge was automatically disabled September 17, 2026 21:32

Head branch was pushed to by a user without write access

@mmastrac
mmastrac force-pushed the dgemma-logprob-token-ids branch from a6f1b01 to c6d8cc1 Compare September 17, 2026 21:32
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/ci run

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❌ This PR is 6 commits behind upstream main. Your branch must contain every commit currently on upstream main. No new CI build was started. Merge or rebase onto the latest main, then rerun /ci run. To test this branch at your own risk, use /ci run --allow-stale.

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mmastrac force-pushed the dgemma-logprob-token-ids branch from c6d8cc1 to 04addc9 Compare September 17, 2026 23:03
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/ci run

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❌ This PR is 2 commits behind upstream main. Your branch must contain every commit currently on upstream main. No new CI build was started. Merge or rebase onto the latest main, then rerun /ci run. To test this branch at your own risk, use /ci run --allow-stale.

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/ci run --allow-stale

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✅ Triggered Buildkite CI #89741 for commit 04addc9916ed.

⚠️ This PR is 2 commits behind upstream main. Running CI at your own risk because --allow-stale was requested; outdated CI configuration may cause failures. Before merging, merge or rebase onto the latest main, then rerun /ci run on the latest PR commit.

The logprobs stashed on a request's converging step went through the
top-k path only, so a request's logprob_token_ids were ignored. For a
choice over many single-token options that is a real defect: at a 26-way
slot only one to eight of the options rank in the top 20, the rest get no
value, and the answer changes with the k requested (measured: Swahili at
k=10, Greek at k=20 and 32, with most of the mass on tokens that spell the
option name).

The sampler now keeps the logprob token-id state like the autoregressive
sampler does and passes it to compute_topk_scores with a per-row slot
mapping, so every requested id gets its exact logprob at every canvas
position.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Signed-off-by: Matt Mastracci <matthew@mastracci.com>
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mmastrac force-pushed the dgemma-logprob-token-ids branch from 04addc9 to f31f54b Compare September 18, 2026 00:34
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/ci run --allow-stale

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✅ Triggered Buildkite CI #89763 for commit f31f54bb22f5.

⚠️ This PR is 4 commits behind upstream main. Running CI at your own risk because --allow-stale was requested; outdated CI configuration may cause failures. Before merging, merge or rebase onto the latest main, then rerun /ci run on the latest PR commit.

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