The State of AI Post-Training Agents

Thoughtful · 3 months ago · 52

Anthropic tested how well frontier AI models can improve other models through post-training on FrogsGame, a puzzle task. Claude Fable 5 achieved 30.9% pass@4 on the benchmark, a 3x improvement over previous Claude models, by discovering how to generate high-quality synthetic training data from a deterministic algorithm rather than the weak base model. The results suggest frontier models are improving at research-level decision-making in post-training, moving beyond generic recipes toward understanding data quality and evaluation as the core bottlenecks.