OpenAI says using its Responses API harness with GPT-5.6 Sol tripled its ARC-AGI-3 score and used fewer tokens, after Sol with the official harness scored 7.8% (OpenAI)

OpenAI announced that using its Responses API harness with GPT-5.6 Sol significantly improved performance on the ARC-AGI-3 benchmark. This combination tripled the ARC-AGI-3 score and consumed fewer tokens compared to when Sol used the official harness, which achieved a 7.8% score. This indicates a notable efficiency and accuracy gain for GPT-5.6 Sol with the custom harness.