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One more thing…
Northeastern & Stanford · Agent runtime
Meet Shepherd: An Open-Source Python Substrate That Lets Meta-Agents Fork, Replay, and Revert Any Agent Run
A coding agent at step 10 is holding edited files, a running dev server, installed packages, and a warm prompt cache. It misreads a traceback and rewrites a file that was already correct. Now you have two bad options: patch forward, growing the context and the token bill, or restart, re-paying every model and tool call while reproducing nothing exactly, because runs are non-deterministic.
What you want is step eight. Git versions files, not a live process or a cache, so no existing runtime offers it. Shepherd records an agent run as a Git-like trace of typed events, where each commit covers the agent process and the filesystem together, copy-on-write. A branch therefore carries live state, not just files. Core operations are mechanized in Lean, and permissions are declared in the signature — a May[GitRepo, ReadOnly] binding compiles down to that run’s writable roots and is enforced at the syscall jail.
Reported: forks 5× faster than Docker and over 95% prompt-cache reuse on replay. Once a run is forkable, a meta-agent can sit on top of it. Live supervision raised CooperBench pair-coding pass rates from 28.8% to 54.7%. Branching exploration beat baselines across four benchmarks by up to 11 points while cutting wall-clock time by up to 58%. Forking rollouts for Tree-RL moved TerminalBench-2 from 34.2% to 39.4%. MIT-licensed, pip install shepherd-ai, Python 3.11+, early alpha.
Read on Marktechpost → · GitHub · PyPI · Project page
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