{
  "slug": "verified-cairo",
  "name": "Verified Cairo AIR (Stone and S-two)",
  "tagline": "StarkWare's Lean 4 soundness proofs of the Cairo VM AIR",
  "maintainer": "StarkWare with Jeremy Avigad and Yoav Seginer",
  "url": "https://arxiv.org/abs/2606.04311",
  "category": "zk-circuits",
  "targets": [
    "Cairo VM AIR",
    "Stone",
    "S-two"
  ],
  "approach": "Lean 4 proofs that AIR satisfiability implies a correct Cairo execution; Sierra-to-CASM building blocks",
  "license": "Open source",
  "status": "Active (paper June 2026); in-house at StarkWare, not a service",
  "summary": "StarkWare, with Jeremy Avigad and Yoav Seginer, has proved in Lean 4 that satisfying the Cairo VM's AIR (for both the Stone and S-two provers) implies a correct Cairo execution, and in July 2026 used the same methodology to verify the STRK20 privacy pool with more than 230 theorems.",
  "details": [
    "This is the longest-running production zkVM verification effort and the model for 'AIR soundness' work elsewhere. Nethermind's Horus, which verified Cairo 0 contracts with SMT, was archived on 2026-09-09; the Lean route is now the only maintained one for Cairo."
  ],
  "strengths": [
    "Whole-VM soundness statement for a deployed prover.",
    "Long track record and academic rigour.",
    "Extended to an application (STRK20)."
  ],
  "limits": [
    "Cairo specific and in-house.",
    "Not packaged as a reusable framework.",
    "Completeness is not the headline property."
  ],
  "fit": [
    "If you build on Starknet, read the papers to understand what is and is not covered by StarkWare's proofs."
  ],
  "references": [
    [
      "Lean 4 soundness of the S-two Cairo AIR (arXiv 2606.04311)",
      "https://arxiv.org/abs/2606.04311"
    ],
    [
      "STRK20 formal verification (2026-07-23)",
      "https://starkware.co/blog/strk20-formal-verification/"
    ],
    [
      "Horus archived (2026-09-09)",
      "https://github.com/NethermindEth/horus-checker"
    ]
  ],
  "category_name": "ZK circuit verification",
  "page": "https://sorryfree.com/frameworks/verified-cairo/",
  "updated": "2026-09-13"
}