Reasonable Team Publishes TLA+ Tutorial: Not a Silver Bullet, AI Agents Could Change That
fhuszar · x · 2026-09-26
After Boris Cherny's viral tweet using Opus 5.5 to model the Claude Agent SDK in TLA+ and Lean (1M views), Ferenc Huszár's Reasonable team published a full tutorial. Key points:
- What TLA+ is: a 30+ year-old formal toolkit for describing allowed system behaviors and invariant/liveness properties.
- Not a silver bullet: TLA+ checks a model of software, not the software itself, and its main model checker only explores finite instances—so it can't fully verify implementations.
- The direction: combining temporal specifications, modern proof systems, and AI agents—from modeling behavior to generating machine-checked proofs—toward software specified, implemented, and verified in one loop.
- Their own work: a sneak peek at Reasonable's efforts to make this loop real, plus an interactive TLA+ playground.
The post also cites Datadog's harness-first agents as early evidence TLA+ pays off in agentic coding.
Related event: Claude Team's Viral Tweet Revives Interest in TLA+ Formal Verification(2 posts)→
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