Update README with conversion note about key format compatibility

README.md

@@ -32,9 +32,23 @@ SAM3 (Segment Anything Model 3) is Meta AI's state-of-the-art foundation model f
 
 | File | Description |
 |---|---|
-| `sam3.safetensors` | Model weights (safetensors format) |
+| `sam3.safetensors` | Model weights (safetensors format, converted from official `.pt`) |
 | `LICENSE` | SAM License (required for redistribution) |
 
+## ⚠️ Conversion Note
+
+The `sam3.safetensors` in this repo is converted **directly from the official `sam3.pt`** checkpoint using:
+
+```python
+import torch
+from safetensors.torch import save_file
+
+state_dict = torch.load("sam3.pt", map_location="cpu")
+save_file(state_dict, "sam3.safetensors")
+```
+
+This preserves the original key names (`detector.*`, `tracker.*`). Do **not** use the HuggingFace Transformers-format safetensors from `facebook/sam3` — those have different key names (`detector_model.*`) and are **incompatible** with `build_sam3_video_model()`.
+
 ## Usage
 
 ```python