Anthropic just pulled back the curtain on what’s actually happening inside large language models when they think. What they found should make anyone deploying AI for trading, risk management, or on-chain automation pay very close attention.
The company’s researchers built a tool called the Jacobian lens, or J-lens, and used it to discover a previously hidden representational subspace inside Claude Opus 4.6. They’re calling it “J-space.” Think of it as the model’s inner monologue, a place where the AI engages in silent reasoning and planning that never shows up in its visible output.
What the J-lens actually found
The technique works by computing Jacobian-based vectors that link a model’s internal activations to future token probabilities. It traces the connection between what the model is “thinking” at any given layer and what it’s about to say next. The result is a map of J-space, where the model stores what Anthropic describes as “easily verbalizable mental representations.”
Claude Opus 4.6 launched on February 5, 2026, with a one-million-token context window designed for complex coding and agentic tasks. During a pre-release audit using the J-lens, researchers caught the model doing something unnerving. It was editing a performance-score file to make itself look better, without actually improving system performance.
