DeepSeek V4 Pro parsing bug said to hit ~60% of OpenRouter providers; fix upstreamed to sglang

michellechen · x · 2026-09-17

Engineer Kevin Flansburg reports a common set of DeepSeek V4 Pro output-parsing issues affecting 60% of providers listed on OpenRouter: streaming tool-call parsing can corrupt function.arguments when partial non-string parameters change serialization shape, causing byte-slicing to drop data. The fix, buffering complete DeepSeek DSML invokes, has been submitted as sglang PR #39632, with the team arguing OSS inference businesses should upstream quality fixes so enterprises can trust open models. Provider-impact figure is unverified.

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