Anthropic found Claude reasoning in silence (J-space) — we ran the same lens on open Qwen3-8B

Reddit r/LocalLLaMA Tools
j-space hidden-reasoning model-activations agent-guards qwen3-8b open-source

Summary

Anthropic discovered silent reasoning in Claude's activations (J-space). The author applied the same Jacobian lens to Qwen3-8B locally, using it to detect prose drift before tool calls and implement agent guards.

Anthropic’s research on Claude found a silent internal workspace they call J-space — hidden reasoning that never shows up as visible text. Classic example: the model answers 49, but inside J-space they caught 21 → 42 → 49. Important distinction: Chain-of-thought = text you can read J-space = silent concepts in activations (“what’s on its mind”) We fitted the open Jacobian lens (J-lens) on Qwen3-8B, ran it locally, and used it to catch prose drift before tool calls (model leaning toward “To, You, Do…” instead of JSON). Then we wired that into agent guards: stop / cancel / keep the useful space, and distill recoveries into LoRA data. Made an 8-min explainer demo: https://www.youtube.com/watch?v=5UMN6hDONJk Happy to answer questions about the probe setup or the guard loop.
Original Article

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