---
license: mit
language:
- en
library_name: transformers
pipeline_tag: reinforcement-learning
tags:
- robotics
- vla
- vision-language-action
- openvla
- omnivla
- robot
- qwen
- dinov2
- siglip
datasets:
- libero_90
- cast
model-index:
- name: openvla-micro
  results: []
---

# OpenVLA-Micro

**A drop-in replacement for OmniVLA 7B that runs ~14× faster with 0.997 action cosine similarity.**

OpenVLA-Micro is a compact Vision-Language-Action model that replaces OmniVLA 7B (DINOv2-L + SigLIP-so400m + Llama-2 7B) with a much smaller stack (DINOv2-S/14 + SigLIP-B/16 + Qwen2.5 0.5B) while preserving compatibility with OmniVLA's pretrained action head through a learned hidden-state shim (896→4096).

## Model Architecture

| Component | Encoder | Output Dim |
|---|---|---|
| Vision (DINO) | `DINOv2-S/14` (facebook/dinov2-small) | 256 tokens × 384d → MLP → 8704 |
| Vision (SigLIP) | `SigLIP-B/16` (google/siglip-base-patch16-224) | 196 tokens × 768d → MLP → 8704 |
| Projector | Linear(8704→896) + GELU + Linear(896→896) | 452 tokens × 896d |
| LLM | `Qwen2.5-0.5B` (24 layers, 896 hidden, 8 heads) | Variable × 896d |
| Shim | Linear(896→2048) + GELU + Linear(2048→4096) | 32 action tokens × 4096d |
| Action Head | OmniVLA's pretrained head (unchanged) | 8 chunks × 7-DoF |

Total parameters: **~0.6B** (vs 7B for OmniVLA/OpenVLA).

## Performance

### vs OmniVLA 7B (teacher)

| Metric | Value | Note |
|---|---|---|
| Hidden state cosine | **0.63** | Last-layer HS at action positions |
| Action cosine | **0.997** | After OmniVLA action head |
| Action MSE | ~0.001 | Effectively identical predictions |
| Inference speed | **~14× faster** | 0.5B vs 7B LLM |

Trained on 1000 CAST episodes (17k steps) via hidden-state distillation. The shim was trained for ~21k steps (plateaued at ~8k).

### vs OpenVLA 7B (original)

OpenVLA-Micro is distilled from *OmniVLA*, which itself fine-tuned *OpenVLA* with 32 action tokens and a modified action head. Direct comparison with the original OpenVLA is not apples-to-apples due to different action tokenization, but the ~14× speedup and near-lossless action quality relative to OmniVLA apply similarly vs OpenVLA.

## Quick Start

```python
from PIL import Image
from modeling_openvla_micro import OpenVLAMicro

model = OpenVLAMicro.from_pretrained("theguy21/openvla-micro", device="cuda")
model.eval()

image = Image.open("demo.jpg").convert("RGB")
action = model.predict_action(image, "pick up the red block")
print(action)  # [0.12, -0.03, 0.45, -0.01, 0.22, 0.08, -0.15]
```

### CLI — GPU

```bash
python inference.py --image demo.jpg "pick up the red block"
```

### CLI — CPU / Edge

```bash
# Standard CPU (~6GB RAM, 3-5 sec/step)
python inference_cpu.py --image demo.jpg "pick up the red block"

# Low-RAM CPU (~2.5GB RAM, requires bitsandbytes)
python inference_cpu.py --low-ram --image demo.jpg "pick up the red block"
```

### As an OmniVLA drop-in replacement

Use `OpenVLAMicroWrapper` (from `model_wrapper.py`) to expose the same forward interface as OmniVLA's `VLAForActionPrediction`:

```python
from model_wrapper import OpenVLAMicroWrapper
from modeling_openvla_micro import DinoSigLIPEncoder, CombinedProjector, ShimMLP

ckpt = torch.load("openvla-micro-distill.pt", map_location="cpu")
ve = DinoSigLIPEncoder()
ve.load_state_dict(ckpt["model"]["vision_backbone"])
# ... (see model_wrapper.py for full example)

output = vla(input_ids, attention_mask, pixel_values, labels=labels, output_hidden_states=True)
actions_hidden_states = extract_actions(output.hidden_states[-1], labels)
predicted_actions = omnivla_action_head.predict_action(actions_hidden_states, modality_id)
```

## Architecture Diagram

```
Image (224×224)
  ├── DINOv2-S/14 → 256 patches × 384d → ShimMLP(384→8704)
  └── SigLIP-B/16 → 196 patches × 768d → ShimMLP(768→8704)
       └── Concat (452 tokens) → Linear(8704→896) → GELU → Linear(896→896)
              └── Qwen2.5 0.5B (24 layers, 896 hidden)
                     └── Hidden State Shim (896→2048→4096)
                            └── OmniVLA Action Head (pretrained, frozen)
                                   └── 8 chunks × 7-DoF actions
```

## Files

| File | Size | Description |
|---|---|---|
| `modeling_openvla_micro.py` | 15 KB | Model definitions |
| `model_wrapper.py` | 11 KB | OmniVLA-compatible interface |
| `inference.py` | 1.5 KB | GPU/CPU CLI inference |
| `inference_cpu.py` | 2 KB | Edge device inference (with low-RAM mode) |
| `train_shim.py` | 15 KB | Reference shim training script |
| `config.json` | 1.2 KB | Model configuration |
| `openvla-micro-merged.pt` | 1.6 GB | Base checkpoint (no shim, 896-dim output) |
| `openvla-micro-distill.pt` | 1.6 GB | Full checkpoint (with baked-in shim, 4096-dim) |

**Which checkpoint to use?**

- `openvla-micro-distill.pt` — **recommended**. Outputs 4096-dim hidden states that plug directly into OmniVLA's action head. One-step inference.
- `openvla-micro-merged.pt` — base model only (896-dim). Use if you want to train your own shim or action head.

## Requirements

```
torch>=2.0.0
torchvision>=0.15.0
transformers>=4.38.0
timm>=0.9.0
Pillow>=10.0.0
numpy>=1.24.0
```

For low-RAM CPU: `bitsandbytes>=0.43.0`

## Training the Shim

```bash
python train_shim.py \
    --cache-dir ./teacher_cache \
    --data-dir ./dataset \
    --base-model openvla-micro-merged.pt \
    --teacher-dim 4096
```

See `train_shim.py` for full options. The script expects pre-cached teacher hidden states; adapt `DistillDataset` to your format.

## License

MIT