LC-IL: language critiques turn suboptimal demos into robot skills, +7 pts over baselines

shaohua0116 · x · 2026-11-13

Presented at CoRL 2026 workshops, Language-Critique Imitation Learning (LC-IL) teaches robots from imperfect demos by labeling what to do, what went wrong, and how to correct it—via structured language critiques (task progress, action quality, movement guidance) generated per frame. A fine-tuned SmolLM2-135M captioner and a differentiable LC-loss plug into BC and diffusion policies (LC-BC/LC-DP) with zero test-time overhead. Across 7 continuous-control tasks, LC-BC averages 67.7 and LC-DP 72.6, beating BC, DPO, ILWD, and DemIDIE by 7+ points; it hits 87% with only 33% expert purity in mixed-quality data and 92.6% with just 10% expert demos.

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