Anthropic Open-Sources j-lens Interpretability Tool

eyishazyer · x · 2026-07-15

The post mentions that Anthropic has open-sourced a tool used to "read what Claude is thinking before it speaks," named Jacobian Lens (j-lens).

The core claim is that they used it to discover something called j-space: a set of tiny internal directions that can capture the concept a model is about to talk about before it writes the first word. The author emphasizes that a challenge with such tools is usually the need to manually pre-select directions to observe, whereas this method attempts to locate these concepts directly from internal representations.

Related event: Anthropic Open-Sources Jacobian Lens for Claude(3 posts)→

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