Chain Lens: Training-Free Multi-Token Hidden-State Readout by Reusing MTP Heads

voooooogel · x · 2026-11-12

voooooogel published a LessWrong post introducing the chain lens, a new interpretability technique that extends single-token lenses like the J-lens into multi-token readouts without any training.

The trick: OSS models already ship MTP (multi-token prediction) heads that take a hidden state and predict future tokens, normally for speculative decoding. The authors feed the J-lens-transported hidden state into the MTP head and sample from it like a language model to roll out a token sequence verbalizing the state. Refinements such as contrastive decoding against a generic hidden-state prior further improve results.

Related event: Chain Lens: Training-Free Multi-Token Readout from Model Activations(6 posts)→

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