Selective traces beat raw volume in coding agents
Training data quality is the clearest lever in this period’s agent work. STITCH filters long software-agent traces down to decision-critical segments, then fine-tunes on that smaller set. The reported gains are large: up to 63.16% relative improvement on SWE-bench Verified, 43.75% on Multi-SWE-bench Java with CodeArts Agent, and a 61.31% compilation pass rate on HarmonyOS ArkTS with less than 1K training trajectories. In parallel, Gentoo shows the same preference for structured signal at inference time. Its agent writes target-specific fuzz generators that beat human-written generators on 6 of 7 Java benchmarks, with average coverage gains of 11% to 21%. Coverage-guided mutation adds under 3% for agent-written generators in typical cases, which suggests the value is in encoding the right constraints early, not in spraying more random search later.