PostHog's Jeeves: a 9B decision model scoring 0.935 on JevBench

petrusenko_max · x · 2026-09-29

PostHog introduced Jeeves, a 9B Jev-like decision model built on Qwen3.5-9B with a LoRA adapter, pointer head, and a block-4 diffusion drafter, trained via SFT and CISPO. It scores 0.889 on held-out test data vs 0.822 for Kev-9B and 0.857 for Jev, and 0.935 vs 0.866 on JevBench public tiers.

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