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RoboMonkey: Scaling Test-Time Sampling and Verification for Vision-Language-Action Models

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arxiv 2506.17811 v2 pith:MHJA455F submitted 2025-06-21 cs.RO cs.AIcs.SYeess.SY

RoboMonkey: Scaling Test-Time Sampling and Verification for Vision-Language-Action Models

classification cs.RO cs.AIcs.SYeess.SY
keywords vlasactionscalingrobomonkeytest-timeverificationdemonstratefine-tuning
verification ladder T0 review T1 audit T2 compute T3 formal T4 reserved
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Vision-Language-Action (VLA) models have demonstrated remarkable capabilities in visuomotor control, yet ensuring their robustness in unstructured real-world environments remains a persistent challenge. In this paper, we investigate test-time scaling through the lens of sampling and verification as means to enhance the robustness and generalization of VLAs. We first demonstrate that the relationship between action error and the number of generated samples follows an exponentiated power law across a range of VLAs, indicating the existence of inference-time scaling laws. Building on these insights, we introduce RoboMonkey, a test-time scaling framework for VLAs. At deployment, RoboMonkey samples a small set of actions from a VLA, applies Gaussian perturbation and majority voting to construct an action proposal distribution, and then uses a Vision Language Model (VLM)-based verifier to select the optimal action. We propose a synthetic data generation pipeline for training such VLM-based action verifiers, and demonstrate that scaling the synthetic dataset consistently improves verification and downstream accuracy. Through extensive simulated and hardware experiments, we show that pairing existing VLAs with RoboMonkey yields significant performance gains, achieving a 25% absolute improvement on out-of-distribution tasks and 9% on in-distribution tasks. Additionally, when adapting to new robot setups, we show that fine-tuning both VLAs and action verifiers yields a 7% performance increase compared to fine-tuning VLAs alone.

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Cited by 29 Pith papers

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score.

  1. Improving Robotic Generalist Policies via Flow Reversal Steering

    cs.RO 2026-06 unverdicted novelty 7.0

    Flow Reversal Steering steers flow matching generalist policies by reversing suboptimal actions to nearby better modes, enabling improved zero-shot control, quick distillation, and RL bootstrapping in robotic manipulation.

  2. Q-VGM: Q-Value-Gradient Matching for Off-Policy Reinforcement Learning of Flow-Matching VLA

    cs.RO 2026-06 unverdicted novelty 7.0

    Q-VGM introduces value-gradient matching via VGG-Flow to improve flow-matching VLA policies with a Cal-QL critic, achieving success rate lifts on LIBERO, RoboTwin, and real-robot tasks.

  3. BOKBO (Best of K Bad Options): Calibrated Abstention for VLA Policies

    cs.LG 2026-05 unverdicted novelty 7.0

    BOKBO is the first conformal abstention method for K-sample VLA policies that supplies finite-sample distribution-free guarantees on executed violation rates, with global and Mondrian per-task variants.

  4. Think Twice, Act Once: Verifier-Guided Action Selection For Embodied Agents

    cs.AI 2026-05 unverdicted novelty 7.0

    VeGAS improves MLLM-based embodied agents by sampling action ensembles and using a verifier trained on LLM-synthesized failure cases, yielding up to 36% relative gains on hard multi-object long-horizon tasks in Habita...

  5. World Action Verifier: Self-Improving World Models via Forward-Inverse Asymmetry

    cs.LG 2026-04 accept novelty 7.0

    WAV self-improves action-conditioned world models by cycle-consistent verification of state plausibility and sparse action reachability, doubling sample efficiency and lifting policy reward by over 22% on nine tasks.

  6. When to Act, Ask, or Learn: Uncertainty-Aware Policy Steering

    cs.RO 2026-02 unverdicted novelty 7.0

    UPS framework uses conformal prediction to calibrate VLM verifiers for choosing between high-confidence action execution, natural language task queries, or policy interventions, then applies residual learning from int...

  7. Verifier-free Test-Time Sampling for Vision-Language-Action Models

    cs.RO 2025-10 conditional novelty 7.0

    A verifier-free test-time sampling method for vision-language-action models that selects actions by KL divergence to a condition-masked reference distribution, improving task success rates.

  8. Action Chunk Scheduling for Batched Robot Policy Serving

    cs.RO 2026-07 conditional novelty 6.0

    A lookahead scheduler that simulates each robot's action-queue state before choosing batches improves throughput in heterogeneous multi-robot policy serving by up to 18% in real-world tests.

  9. Addressing the Orchestration Gap in Generalist Robots via Physical Agency

    cs.RO 2026-07 conditional novelty 6.0

    A closed-loop inference-time orchestrator using a frontier VLM lifts frozen robot policies from 12.8% to 53.3% on LIBERO-PRO and from near-zero to over 90% on reasoning-limited real-robot tasks, without retraining the...

  10. ELASTIC: Efficiently Learning to Adaptively Scale Test-Time Compute for Generative Control Policies

    cs.RO 2026-06 unverdicted novelty 6.0

    ELASTIC learns a state-dependent meta-policy that allocates sequential and parallel test-time compute for generative control policies, outperforming fixed baselines in simulation and reducing real-robot latency by 34%...

  11. Sequential Planning via Anchored Robotic Keypoints

    cs.RO 2026-06 unverdicted novelty 6.0

    SPARK reaches 43.7% success on six LIBERO-PRO cells by LLM-generated typed behavior trees plus multi-prompt perception and recovery, more than doubling CaP-Agent0 and VLA baselines.

  12. E-TTS: A New Embodied Test-Time Scaling Framework for Robotic Manipulation

    cs.RO 2026-06 unverdicted novelty 6.0

    E-TTS introduces a plug-and-play test-time scaling method for embodied tasks that unifies reasoning-action sampling with history buffers and closed-loop refinement to improve performance on manipulation benchmarks.

  13. Neglected Free Lunch from Post-training: Progress Advantage for LLM Agents

    cs.LG 2026-06 unverdicted novelty 6.0

    The log-probability ratio from RL post-training recovers the optimal advantage function, providing an effective free signal for test-time scaling, uncertainty estimation, and failure attribution in LLM agents.

  14. DREAM-Chunk: Reactive Action Chunking with Latent World Model

    cs.RO 2026-06 unverdicted novelty 6.0

    DREAM-Chunk uses test-time sampling and latent-world-model rollouts to select robust action chunks from chunking-based VLA policies, improving performance under stochastic dynamics on simulation and hardware tasks.

  15. VeriSpace: Spatially Grounded Action Verification for Vision-Language-Action Models

    cs.RO 2026-06 unverdicted novelty 6.0

    VeriSpace is a 3D-aware action verifier that improves test-time action selection in VLA models by encoding scenes with visual and geometric information and reasoning over spatial relations and goal progress.

  16. Q-VGM: Q-Value-Gradient Matching for Off-Policy Reinforcement Learning of Flow-Matching VLA

    cs.RO 2026-06 conditional novelty 6.0

    Q-VGM offline RL fine-tuning converts critic Q-gradients into residual velocity targets for flow-matching VLAs, raising LIBERO success from 75.0% to 92.5%.

  17. Retrieve-then-Steer: Online Success Memory for Test-Time Adaptation of Generative VLAs

    cs.RO 2026-05 unverdicted novelty 6.0

    Retrieve-then-steer stores successful observation-action segments in memory, retrieves relevant chunks, filters them, and uses an elite prior with confidence-adaptive guidance to steer a flow-matching action sampler f...

  18. Retrieve-then-Steer: Online Success Memory for Test-Time Adaptation of Generative VLAs

    cs.RO 2026-05 unverdicted novelty 6.0

    A retrieve-then-steer method stores successful robot actions in memory and uses them to steer a frozen VLA's flow-matching sampler for better test-time reliability without parameter updates.

  19. VLA-ATTC: Adaptive Test-Time Compute for VLA Models with Relative Action Critic Model

    cs.RO 2026-05 unverdicted novelty 6.0

    VLA-ATTC equips VLA models with adaptive test-time compute via an uncertainty clutch and relative action critic, cutting failure rates by over 50% on LIBERO-LONG.

  20. FASTER: Value-Guided Sampling for Fast RL

    cs.LG 2026-04 unverdicted novelty 6.0

    FASTER models multi-candidate denoising as an MDP and trains a value function to filter actions early, delivering the performance of full sampling at lower cost in diffusion RL policies.

  21. Test-Time Perturbation Learning with Delayed Feedback for Vision-Language-Action Models

    cs.CV 2026-04 unverdicted novelty 6.0

    PDF improves VLA success rates on LIBERO and Atari by applying test-time perturbation learning with delayed feedback to correct trajectory overfitting and overconfidence.

  22. A1: A Fully Transparent Open-Source, Adaptive and Efficient Truncated Vision-Language-Action Model

    cs.RO 2026-04 unverdicted novelty 6.0

    A1 is a transparent VLA framework achieving state-of-the-art robot manipulation success with up to 72% lower latency via adaptive layer truncation and inter-layer flow matching.

  23. Steerable Vision-Language-Action Policies for Embodied Reasoning and Hierarchical Control

    cs.RO 2026-02 unverdicted novelty 6.0

    Steerable VLAs trained on rich synthetic commands at subtask, motion, and pixel levels enable VLMs to steer robot behavior more effectively, outperforming prior hierarchical baselines on real-world manipulation and ge...

  24. EVE: A Generator-Verifier System for Generative Policies

    cs.RO 2025-12 conditional novelty 6.0

    Zero-shot VLM verifiers, ensembled and fused via guided diffusion, improve frozen generative robot policies' success rates by 1-2 percentage points on simulated manipulation tasks.

  25. A Survey on Vision-Language-Action Models for Embodied AI

    cs.RO 2024-05 unverdicted novelty 6.0

    This is the first survey on vision-language-action models, providing a taxonomy across three lines, plus summaries of datasets, simulators, benchmarks, challenges, and future directions in embodied AI.

  26. FORCE: Efficient VLA Reinforcement Fine-Tuning via Value-Calibrated Warm-up and Self-Distillation

    cs.RO 2026-06 unverdicted novelty 5.0

    FORCE is a 3-stage RL fine-tuning method for VLA models that stabilizes Q-function via on-policy warm-up and filters high-value actions for updates, claiming 79% success rate gains and 32.5% faster training without hu...

  27. TEXEDO : Test Time Scaling for Controller-aware Language-conditioned Humanoid Motion Generation

    cs.RO 2026-06 unverdicted novelty 5.0

    TEXEDO uses test-time sampling and a combined feasibility-semantic reward model to select executable, text-aligned motions for humanoid robots from a pretrained generator.

  28. Test-Time Scaling in Multimodal Foundation Models: A Comprehensive Survey of Generation and Reasoning

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    A survey of test-time scaling for multimodal foundation models that introduces a three-way taxonomy of sampling, feedback, and search approaches along with applications and benchmarks.

  29. Position: Good Embodied Reward Models Need Bad Behavior Data

    cs.RO 2026-05 unverdicted novelty 4.0

    Embodied reward models systematically over-reward unsafe, suboptimal, and shortcut robot behaviors due to training on successful data only, and modest inclusion of bad behavior data improves alignment with human preferences.