The harness doesn't make the model smarter. It stops it from repeatedly becoming stupider.

Reddit r/AI_Agents Tools
ai-harness reasoning-steering arc-agi-benchmark openai-adapter performance-improvement compaction-technique model-optimization

Summary

The article argues that harnesses for AI models don't boost innate reasoning but steer models to maintain performance, with examples showing a significant improvement on ARC-AGI-3 through state retention and compaction.

Think about it. Harness is not the model. It's a determinate substrate. It doesn't boost model's innate "reasoning". It merely steers it so that you end up with same neural weights but completely different trajectory. For instance, ARC's Standard harness lets the model maintain visible notes, but it's up to the model to decide what to preserve. OpenAI's Provider Adapter that was used for their Astra model, on the other hand, preserves its reasoning state between requests and uses compaction to keep useful history available when conversations grow long. Just by retaining reasoning and replacing rolling truncation with compaction, Astra went from 54.8% on ARC-AGI-3 with ARC's standard harness to 99.9% with OpenAI's own adapter.
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