Sol and Terra outperform GPT-5.5 on the PostTrainBench-Lite self-improvement benchmark, but they still often rely on narrow strategies and sometimes overfit to the eval rather than reliably designing adaptive post-training recipes.

Despite beating GPT-5.5 on a shortened self-improvement benchmark, Sol and Terra tend to collapse to narrow strategies and overfit, suggesting GPT-5.6 is stronger at extended coding execution than at broad, adaptive AI research judgment. ✦ AI generated

Karina Nguyen · Latent Space · 2026-06-27 · original ↗

OpenAI evaluated GPT-5.6 on PostTrainBench-Lite, a shortened version of a benchmark where agents get 5 hours instead of 10 to improve an open-source base model. Karina Nguyen said Sol and Terra outperform GPT-5.5, but still often rely on narrow strategies and sometimes overfit to the eval.

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