140k+ probing runs show joint layer-module selection beats final-layer probing in transformers

Ambroise Odonnat · hf · 2026-11-13

A systematic study asks which representation inside transformer foundation models should be probed. Jointly selecting both the layer and the module (8 modules per block: LN, MHA, FC, residuals, etc.) yields better probing features than depth-only or final-layer approaches, and simple fixed strategies recover much of the gain. The study spans 140,000+ linear probing evaluations across 15 vision foundation models on 18 datasets and 9 LLMs on 24 MTEB tasks, challenging the default assumption that the last layer holds the best representations.

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