[Naveassaf]

Summary

Nemotron3's parser overrides DeepSeek-R1's parser to handle the enable_thinking=False / force_nonempty_content=True cases, where the model is asked to skip thinking but R1's parser still routes everything into reasoning whenever it can't cleanly parse a <think>...</think> block. To recover, the Nemotron parser swaps reasoning with final_content so the answer is delivered as content rather than reasoning.

The swap was gated on final_content is None, which misses the case where the model emits whitespace-only content (e.g. a stray "\n" or " " after ). In that case final_content is a non-None string, the swap is skipped, and the client receives whitespace as the response while the actual answer remains stranded in reasoning.

This PR changes the Nemotron3 parser to match the upstream model-side fix shipped in the Nemotron Super checkpoint: https://huggingface.co/nvidia/NVIDIA-Nemotron-3-Super-120B-A12B-NVFP4/commit/4f0cf9daaeb7a4d5e23f80a00e7ed15f0e03caf6

[claude]

Claude Code Review

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[gemini-code-assist]

Code Review

This pull request updates the NemotronV3ReasoningParser to treat whitespace-only final_content as empty when deciding whether to swap it with the reasoning field. Feedback suggests refining this logic to ensure the swap only occurs if the reasoning field itself contains non-whitespace content, preventing redundant or potentially invalid swaps.

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vllm/reasoning/nemotron_v3_reasoning_parser.py (29)

The current logic swaps reasoning and final_content whenever final_content is empty or whitespace. However, if reasoning is also None or whitespace-only, this swap could result in final_content becoming None (if reasoning was None) or remaining whitespace-only. This doesn't help 'rescue' an answer and might even violate the intent of force_nonempty_content by replacing a whitespace string with None. It is safer to only perform the swap if there is actual non-whitespace content in the reasoning field to be rescued.

            and (final_content is None or not final_content.strip())
            and (reasoning and reasoning.strip())

[bbrowning]

Ideally we'd also add a test for this case to prevent regression. However, given that this exactly matches the change already merged upstream in the model's HuggingFace repo and it's a very small change, will approve this as-is.

If you're up for it, I'd happily approve a follow-up PR to add some additional unit test coverage for this reasoning parser for this or other edge cases it handles but that isn't covered by tests.