Fathom Mode

Most AI agents fail not because they reason poorly, but because they reason faithfully from a misread intent. Fathom Mode for Claude targets this failure mode, called Intent Decay: at 85% per-step accuracy, a 10-step agent pipeline delivers only 19.7% end-to-end reliability. It is a planning-session protocol that runs before Claude acts, in both Claude Code and Cowork. Opus 4.7 carries the dialogue: it restates its understanding, surfaces missing details, catches technical misconceptions, and asks one focused question per turn. A deterministic Python core handles the rest, maintaining an Intent Graph, the Fathom Score, Causal Provenance, and a zero-LLM compile step that turns the dialogue into a reviewable plan. The key invariant: Claude may infer supporting structure, but user-stated causal reasoning is kept separate from system-inferred structure before any code is written. After one approval, Claude executes from the compiled plan. The demo shows two real tasks: a daily-work review producing a personalized PDF, and a chaos-theory visualization where Fathom catches the user's Lotka-Volterra misconception in the first turn.