THE STATE OF AI POST-TRAINING AGENTS

Summary from the TLDR Dev newsletter

Recent evaluations of advanced AI models, including Claude Fable 5, Opus 4.8, and GPT-5.5, show improvements in their ability to improve a fixed base model through post-training tasks like FrogsGame. Important advancements include better data quality generation, effective strategies for reinforcement learning, and the ability to calibrate self-evaluations, with Fable 5 being the best by producing high-quality training traces and effectively using time.