Mosaic: multi-session agentic RL with hierarchical advantage estimation

LARK-Lab · hf · 2026-10-16

LARK-Lab introduces Mosaic, extending agentic reinforcement learning to trajectories spanning multiple sessions. Since agent tasks often cross several conversations, per-trajectory advantage estimation breaks down. Mosaic uses hierarchical advantage estimation to optimize session-level contributions and credit allocation, enabling RL training that covers multiple sessions within a single rollout — a new credit-assignment approach for long-horizon agent training.

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