ResearchResearch paperReinforcement Learning · Large Language Models · Reasoning & Planning1 source · Oct 15, 2026

Harness-Delta Attribution: Dissecting Gains From Harness Evolution

In this work, we introduce Harness-Delta Attribution (HDA), an evaluation protocol that dissects an evolution gain into artifact-driven overfitting, gains explained by test-time scaling, and the remainder, which gives an upper bound on residual generalizable improvement.

Key points

  • Harness evolution automatically optimizes the prompts, skills, tools, and orchestration code around a fixed-weight model, offering a way to improve agentic systems without updating model weights.
  • We apply HDA to 11 executor models and three harness-evolution frameworks across math, coding, creativity, and agentic tasks.
  • In 21 of these settings that show statistically significant search-set gains, we find that a large share of the improvement is explained by overfitting or test-time scaling.
  • These results motivate attribution-aware evaluation in future harness evolution research.

Sources (1)

  • [1]Harness-Delta Attribution: Dissecting Gains From Harness Evolution
    Hugging Face Daily Papers · Oct 15, 12:00 AM
    In this work, we introduce Harness-Delta Attribution (HDA), an evaluation protocol that dissects an evolution gain into artifact-driven overfitting, gains explained by test-time scaling, and the remainder, which gives an upper bound on residual generalizable improvement.
    Harness evolution automatically optimizes the prompts, skills, tools, and orchestration code around a fixed-weight model, offering a way to improve agentic systems without updating model weights.

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