L3M is a runtime written in Lean 4 that keeps all agent state in Git, so a run can be rewound, forked or merged. A tool's review tier follows from how far its effects can be undone.
In the News: October 17, 2026 (Evening)
L3M, a Lean 4 agent harness, tiers tools by how far their effects can be undone, and tools that need no review reach about two thirds of shell pass rate.
Evening edition
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