动察 Beating AI News Flash: Hugging Face has open-sourced a Multi-harness RL solution that can directly plug existing Coding Agents such as Claude Code, Codex, and OpenCode into the reinforcement learning process to train open-source models connected to them, without needing to build a separate training environment for each Agent.
Large model companies such as OpenAI have long been training models in their own Agent environments. This time, Hugging Face has turned similar capabilities into a general open-source tool, allowing other teams to directly use existing Agents for RL.
Moreover, the model does not have to be trained in only one type of Agent. In a single training run, tasks can be run in turn across Claude Code, Codex, OpenCode, and Mini-SWE-Agent, enabling the same model to adapt to different prompts, tools, and execution logic, reducing the "imbalance" of only being good at one kind of Harness.
They tested with a 2.6-billion-parameter small model from Liquid AI. With the same weights and only a change of Agent, the task pass rate could drop from about 62% to 33%. After training simultaneously in four Agent environments, the average pass rate increased from 42.2% to 54.2%, and the improvement across different Agents was also more balanced than training in only a single environment.

