Thinking Machines explains LLM nondeterminism and ships batch-invariant kernels for reproducibility

AccBalanced · x · 2026-10-19

Thinking Machines Lab (Horace He et al.) breaks down why LLM APIs remain nondeterministic even at temperature 0: concurrent execution plus floating-point non-associativity — batched kernels merge requests, so which core finishes first changes results. The fix: batch-invariant kernels enabling deterministic inference. @cHHillee notes this addresses train/inference behavior mismatch, and @Sauers shows a model can be SFT-trained (using layer-34 activations from HF Trainer vs vLLM) to detect whether it's in training or deployment, generalizing from vLLM to SGLang.

Original post →

More from Infra

Infra channel →