J-Space - J-Space
Research explainers on J-Space and the internal workspaces where modern LLMs stage reportable reasoning. How safety teams use interpretability to catch behaviors that tests miss — and make model behavior operational. Deep dives on Anthropic’s interpretability work, internal workspaces in LLMs, and what J-Space reveals about model behavior. That expression formalizes the prose definition. The PDF text used here does not display this equation. How the Activation Controllability Benchmark paper works: a fixed copy task, a 0.85 similarity keep-rule, and residual-stream concept projections. Gao et al.’s logit-diff ablation score measures how sparse an SAE latent’s effect on output logits is. It is not a rule for admitting circuit components. Gao et al. (2024) cite the BERT interpretability illusion as a gloss: random activating examples can make an overly broad feature explanation look right. In arXiv:2412.09565v2 (Bailey et al., 8 Feb 2025), an activation is obfuscated against a named late