MiMo-V2 paper: agentic groupwise grading redistributes RL advantages to curb reward hacks

Sauers_ · x · 2026-10-17

The MiMo-V2 paper details a groupwise agentic grading scheme for code-agent RL. (a) Groupwise Reward Synthesis builds task-specific rubrics (solution + behavior) offline from rollouts, grades trajectories online, and combines reward as test outcome × solution score × behavior score. (b) Groupwise Advantage Redistribution compares passing trajectories online, ranks their quality with a groupwise grader, resets confirmed reward-hack rewards to zero, and redistributes sequence-level positive advantage from low- to high-quality passing solutions — letting the agent choose which trajectories earn positive RL advantage.

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