SWE-Verifier: a 4B model lifts coding agents ~1.7pp on SWE-Bench at 9–13% extra cost

radamihalcea · x · 2026-10-30

Researchers introduce SWE-Verifier, a lightweight 4B generative verifier that selectively guides coding agents roughly 70× its size at critical decision points.

How it works: instead of trajectory-level or all-step verification, it scores each proposed action and only triggers candidate sampling plus ranking when needed. It's trained from Qwen3.5-4B on preference data grouping contrasting actions with environment observations and rubric-guided teacher scores.

Results (SWE-Bench Verified, mini-swe-agent):

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