Steerable but Not Decodable: Function Vectors Operate Beyond the Logit Lens
Activation steering presupposes that task-relevant behaviors correspond to linear directions in activation space -- directions that should both steer the model and be readable along the unembedding. Function vectors (FVs), extracted as mean differences across ICL demonstrations, are the canonical test case; the prediction: steering and decoding succeed or fail together. Across 12 tasks, 6 models from 3 families, and 4,032 directed cross-template pairs, we find the opposite. FV steering routinely succeeds where the logit lens cannot decode the correct answer at any intermediate layer, while the converse -- decodable without steerable -- is nearly empty (3 of 72). The gap is not representat...
| Authors | Mohammed Suhail B Nadaf |
|---|---|
| Primary category | cs.LG |
| Published | 3 April 2026 |
| Last updated at source | 8 May 2026 |
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