StateBridge: Training-free Hidden-state Alignment for Latent Communication in LLM Multi-Agent Systems

TL;DR - StateBridge enables LLM agents to communicate through continuous hidden states using a training-free, closed-form alignment method. It avoids text’s information bottleneck and learned projectors while improving performance across reasoning, coding, and question-answering tasks.

• Aligns sender final-layer states with the receiver’s input space via an orthogonal transformation.
• Uses norm calibration and vocabulary anchoring to maintain compatibility with pretrained input distributions.
• Prepends aligned states to the receiver’s input as a continuous prefix.
• Achieved best or tied-best results on 22 of 26 model-task pairs across four models from two families.