# tinker_cookbook.exceptions.WeightsMergeError

## _class_ [**tinker_cookbook.exceptions.WeightsMergeError**](https://github.com/thinking-machines-lab/tinker-cookbook/blob/main/tinker_cookbook/exceptions.py#L182)( _[WeightsError](https://tinker-docs.thinkingmachines.ai/cookbook/api-reference/exceptions/weightserror/), ValueError_)

Failed to merge LoRA adapter weights into a base model.

Raised when adapter weights are incompatible with the base model (shape mismatches, missing keys, etc.). Inherits from `ValueError` because merge errors are validation failures (wrong shapes, missing config keys).