With the official ARC-AGI-3 harness, GPT-5.6 Sol scored 13.3% on the public task set. On the public leaderboard for the game OpenAI tested with, no frontier model gets past the first level. With the modified harness, GPT-5.6 Sol cleared all six. GPT-5.6 Sol has cleared Pokémon FireRed on a vision-only setup, played through Slay the Spire 2 using Codex’s computer use tools, and made progress on the early stages of Baba Is You. OpenAI reimplemented the ARC-AGI-3 harness this way and replaced rolling truncation with compaction, a Responses API feature that summarizes older context instead of dropping it outright.