The metadata just consists of the total size of the model for now. We plan to add other information in the future:

index["metadata"]
{'total_size': 433245184}

The weights map is the main part of this index, which maps each parameter name (as usually found in a PyTorch model state_dict) to the file it's stored in:

index["weight_map"]
{'embeddings.LayerNorm.bias': 'pytorch_model-00001-of-00003.bin',
 'embeddings.LayerNorm.weight': 'pytorch_model-00001-of-00003.bin',