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[Transformers backend] Support batch-sharded sampling - #66545
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DarkLight1337 merged 2 commits intoNov 9, 2026
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Implement `compute_logits_local` in the backend's `CausalMixin` so that `enable_batch_sharded_sampling` is no longer silently disabled for Transformers modeling backend models, matching native Llama. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Signed-off-by: Harry Mellor <19981378+hmellor@users.noreply.github.com>
This was referenced Nov 9, 2026
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November 9, 2026 11:15
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Tbh we should have defined this method in the model interface but that's outside the scope of this PR. cc @WoosukKwon
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Overview
Add
compute_logits_localto the Transformers modeling backend's causal models, so batch-sharded sampling (enable_batch_sharded_sampling) works for them as it does for native Llama. Part of serving Llama with the backend (#66547).Claims
Validation
B200, Llama-3.2-1B-Instruct, TP=2:
2 passed.
[llama-transformers]fails onmain(AssertionError: [False, False]: the sharded sampler never ran).Pull Request Checklist
I used vLLM's
/pr-checklistskill. (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.
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