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Beyond Data Scaling: Representation-Centric Pre-training for Vision-Language-Action Models
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Proposes VLAct, a representation-centric continued pre-training recipe for VLM-based VLA backbones (shallow-layer freezing, caption co-training, multi-head continuous action supervision, partially unified action layout) that reaches competitive results on LIBERO-Plus, RoboTwin 2.0, RoboDojo and RoboCasa-GR1 using 16 GPUs and open data.
Problem
Under a fixed robot-data budget, VLA continued pre-training tends to over-specialize the VLM backbone to a single action head and embodiment and erodes general vision-language features; the goal is a reusable, transferable VLA backbone.
Approach
Continued pre-training of a Qwen3-VL-4B backbone with frozen vision encoder and lower LLM half, caption co-training, simultaneous OFT/PI/GR00T action heads on a shared latent, and a partially unified cross-embodiment action space with wrap-aware angle loss; the pre-training heads are discarded at fine-tuning.
Key results
- VLAct reaches 82.6% on LIBERO-Plus versus 75.0% for the in-house Qwen3VL-OFT baseline and 80.5% for Abot-M0.
- On RoboTwin 2.0 Data Scaling setting, VLAct-OFT reaches 92.5% Clean and 90.8% Random success.
- On RoboCasa-GR1 with 20% of downstream trajectories, VLAct reaches 49.5%, above full-data GR00T-N1.6 at 47.6%.
Surprising findings
- Pure language instruction data as auxiliary co-training also improves over robot-only pre-training on LIBERO-Plus.
- OFT-only pre-training lowers downstream PI fine-tuning performance below from-scratch (55.1 vs 60.5), indicating head-specific representation collapse.
Limitations
- Memory tasks on RoboDojo remain a clear weakness (0.56% success).
- Comparisons with industrial systems use published numbers under differing training compute and protocols.
- Simulation and real-world experiments are limited in scale; real-world uses 10 trials per task.
Experimental setup
Datasets: DROID InternA1 RoboCoin MolmoAct LLaVA-ReCap-CC3M LLaVA OneVision RefCOCO COCO-ReM PixMo-Points RoboPoint SenseNova-SI-800K Nemotron-SFT-Instruction-Following-Chat-v2
Benchmarks: LIBERO-Plus VLA-Arena RoboTwin 2.0 DOMINO RoboCasa-GR1 RoboDojo
Metrics: success rate average score partial-progress score
Baselines: Qwen3VL-OFT pi0 pi0.5 Abot-M0 GR00T-N1.6 LingBot-VLA X-VLA OpenVLA-OFT StarVLA-alpha X-WAM
Builds on: StarVLA OpenVLA-OFT pi0 GR00T N1.5 FAST
Closest papers by meaning
- PriorVLA: Prior-Preserving Adaptation for Vision-Language-Action Models (NeurIPS 2026 · similarity 0.92)
- ElegantVLA: Learning When to Think for Efficient Vision-Language-Action Models (NeurIPS 2026 · similarity 0.92)
- FineVLA: Fine-Grained Instruction Alignment for Steerable Vision-Language-Action Policies (NeurIPS 2026 · similarity 0.92)
- Knowledge Insulating Vision-Language-Action Models: Train Fast, Run Fast, Generalize Better (NeurIPS 2025 · similarity 0.92)
- NS-VLA: Towards Neuro-Symbolic Vision-Language-Action Models (NeurIPS 2026 · similarity 0.91)
- VLA-REPLICA: A Low-Cost, Reproducible Benchmark for Real-World Evaluation of Vision-Language-Action Models (NeurIPS 2026 · similarity 0.91)
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