OpenAI Reports GPT-5.6 Sol Score Triples on ARC-AGI-3 After Harness Change

daniel_mac8 · x · 2026-08-15

X user danielmac8 posts that OpenAI reported GPT-5.6 Sol jumped from 13.3% to 38.3% on ARC-AGI-3 after enabling retained reasoning and compaction, only changing the harness. This illustrates that model capability and agent capability are different, emphasizing harness engineering. Recommends following DarwinX and AutoDesign.

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