Agent Reinforcement Fine Tuning – Will Hang & Cathy Zhou, OpenAI
Dec 9, 2025 · 16:55
Will Hang and Cathy Zhou of OpenAI's fine-tuning team introduce Agent Reinforcement Fine-Tuning (RFT), a method to improve AI agents by training them end-to-end on tasks involving tool calls and reasoning. They define an agent as a model that interleaves reasoning with external tool interactions, unlike regular models. The hierarchy of optimization moves from prompt engineering to task optimization to RFT, which changes model weights based on a custom reward signal. New features allow models to call tools via public endpoints and use custom rewards hosted externally. Case studies show concrete gains: Cognition improved code edit planning by 10 points with 1,000 examples and reduced tool call steps from 8–10 to 4; Codto's deep research agent boosted recall by 6% while cutting long-tail tool calls (over 15) down to 2–4; Cosine achieved state-of-the-art on enterprise code benchmarks by using strict graders that reward only pass-tested code; and Macco wrote GPU kernels from just 100 PyTorch prompts, beating SOTA by 72% after addressing reward hacking with seven edge-case detectors. Four principles for success: define tasks unambiguously, mirror production traffic in train/eval sets,…
