Observing Open-Source Model Internal States via J-space
Murky-Sign37 · reddit · 2026-07-12
This post covers two main layers: Anthropic's discovery of J-space, an internal working space where Claude "thinks in silence," and the author's application of this analytical approach to open-source model Qwen3-8B via local experiments.
Key takeaways include:
- Meaning of J-space: It is not readable chain-of-thought, but a hidden conceptual space within activations. The model may pass through a series of intermediate internal states before outputting the final answer.
- Experimental method: The author used the open-source Jacobian lens (J-lens) to observe the internal states of Qwen3-8B, locally capturing "prose drift" prior to tool calls—such as a tendency to generate natural language prefixes instead of JSON.
- Engineering utility: This signal was integrated into an agent guard pipeline to halt, cancel, or preserve useful internal states, and the recovered samples were distilled into LoRA data.
- Supplementary materials: The post includes an 8-minute blackboard lecture video and a terminal demo to help understand the probe setup and guard loop implementation.
Related event: Anthropic Reveals Claude's Hidden Reasoning Space: J-space(16 posts)→
More from coding & agent
- Dev builds talk on guardrails workflow for shipping AI-written code without reading it — TejasKumar_ · 2026-09-11
- banteg: Codex auto-review has regressed, blocking steps needed to complete authorized tasks — banteg · 2026-09-11
- A doc-anchored agent workflow: you write, the agent only critiques and finds disagreements — lucasmeijer · 2026-09-11
- SymKit MCP: 44 tools for AI agents to verify symbolic derivations — Foreign-Specific-604 · 2026-09-11
- GitHub Copilot team routes user bug reports to an AI agent via Slack — marlene_zw · 2026-09-11
- Scanning 23 agent sessions, a dev found 3 silent failure modes in memory systems — No_Advertising2536 · 2026-09-11