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LaST-R1: Reinforcing Robotic Manipulation via Adaptive Physical Latent Reasoning
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Proposes LaST-R1, an RL post-training framework (LAPO) that jointly optimizes latent chain-of-thought reasoning and action generation in a VLA, plus an adaptive latent CoT length mechanism, reaching 99.9% on LIBERO from one-shot SFT warm-up.
Problem
Latent-reasoning VLA models are trained only by imitation learning on static demonstrations, limiting adaptability and generalization; existing online RL for VLAs optimizes only action space and ignores the reasoning process.
Approach
LAPO treats latent reasoning embeddings as implicit decision variables and uses a step-level likelihood ratio (a Gaussian-based latent ratio plus action token ratio) so environment rewards shape both latent reasoning and actions; an adaptive <latent_end> token lets the policy choose its reasoning length.
Key results
- Achieves 99.9% average success rate on LIBERO with one-shot SFT warm-up, ranking first on all four suites (vs. pi_RL 98.3%).
- On real-world tasks, average success rises from 52.5% after warm-up to 93.75% after RL, versus 71.25% for full-SFT pi0.5.
- Ablation on LIBERO-Spatial: LAPO with latent reasoning reaches 99.9% vs. Action-Only + PPO 95.2%.
Surprising findings
- Adaptive latent CoT with the RL-optimized policy converges toward short reasoning lengths (2 or 4 tokens dominating), and the paper reports execution steps even below expert demonstrations in most scenarios.
- Setting the candidate-position count M=8 slightly degrades performance relative to M=4.
Limitations
- Real-world evaluation uses only four tasks with 20 rollouts per setting and human-judged success.
- Pre-training dataset is large but the LIBERO and real-world results depend on a one-shot or few-shot warm-up and specific hyperparameters (sigma, lambda weights).
- Latent-ratio derivation assumes isotropic Gaussian latents with fixed variance, an approximation.
Experimental setup
Datasets: LIBERO Open-X-Embodiment DROID RoboMIND
Benchmarks: LIBERO-Spatial LIBERO-Object LIBERO-Goal LIBERO-Long real-world Franka tasks
Metrics: success rate average rank out-of-distribution success rate
Baselines: OpenVLA GR00T-N1 pi0 pi0.5 OpenVLA-OFT GRAPE TGRPO VLA-RL SimpleVLA-RL RLinf-GRPO pi_RL
Builds on: PPO Qwen3-VL SimpleVLA-RL GRAPE DINOv3
Closest papers by meaning
- Robot-R1: Reinforcement Learning for Enhanced Embodied Reasoning in Robotics (NeurIPS 2025 · similarity 0.90)
- SOLE-R1: Video-Language Reasoning as the Sole Reward for On-Robot Reinforcement Learning (NeurIPS 2026 · similarity 0.89)
- Efficient Robotic Policy Learning via Latent Space Backward Planning (ICML 2025 · similarity 0.88)
- Plan-Seq-Learn: Language Model Guided RL for Solving Long Horizon Robotics Tasks (ICLR 2024 · similarity 0.88)
- Multi-Stage Manipulation with Demonstration-Augmented Reward, Policy, and World Model Learning (ICML 2025 · similarity 0.88)
- SOLD: Slot Object-Centric Latent Dynamics Models for Relational Manipulation Learning from Pixels (ICML 2025 · similarity 0.88)
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