Your Code Has Bugs. Lean4 Has Proofs: Formal Verification for Engineers — Varun Pant, AWS
Aug 28, 2026 · 10:07
Varun Pant of AWS argues that formal verification is the only check that can prove AI-generated code correct for every input, as tests and human review cannot scale to the thousands of weekly pull requests coding agents now produce. He advocates spec-driven development with the Lean proof assistant, where humans own the specification and machines own the code and proof, validated by a small independent kernel. Pant walks through Lean's tactics via a chess analogy and details production examples: an AI rewrote zlib in Lean, generating 32,000 lines of proof; Cedar's Lean specification and Rust implementation are reconciled by roughly 100 million differential tests nightly; Verus uses Z3 solvers; and AWS's in-progress Starta tool aims to bring any language into the same verified core.
