Contract Diff: behavioural tests for AI-written Solidity before deploy

The broader category of AI security and testing in CI for Solidity is crowded and well funded. Olympix and Octane already sell into GitHub CI and are both listed as Circle partners, so they are already in front of stablecoin teams. Certora has an open-source product for checking AI-written contracts, and Recon offers cloud fuzzing in CI with AI-generated test suites. The narrower idea still looks open: automatic behavioural-equivalence checks between an agent-edited contract and a reference version. The only purpose-built tool I found, Trail of Bits' Diffusc, was archived in February 2025. None of the commercial products I found market old-versus-new differential fuzzing as their main feature. They look for vulnerabilities or check properties that users write themselves. A new entrant could win by making differential testing work with no setup. That means automatically building the harness that runs the old and new versions side by side, forking the deployed version on-chain as the reference, and treating intended changes as an explicit approved list so that every other change in behaviour fails the build. It could also target what stablecoin and tokenisation teams specifically worry about: mint, burn, freeze, blacklist, role and upgrade-storage behaviour, and how compliance hooks behave across upgrades. The trigger for each check would be an AI agent's pull request, not a manual upgrade. The risk is that this becomes a feature. Olympix, Octane, Recon or Certora could add a diff mode quickly, and Foundry users can write differential harnesses by hand. The audit-firm partner channel looks weaker than it sounds. Several of the closest players are audit firms themselves or are tied to one: Trail of Bits, Cyfrin, Nethermind, and Recon, which also sells to auditors. They would rather use their own tooling than accept a third-party report that cuts their billable hours. I found no sign that any audit firm accepts outside behavioural reports as standard audit input.

• Diffusc (Trail of Bits / crytic)

  The closest match to Diff CI. It is open source, uses Slither and Echidna to differential-fuzz two upgradeable contract implementations before an upgrade, and offers standard, fork and hybrid modes. The repo was archived in February 2025 and is now read-only, so nobody is maintaining it.

• Olympix

  A funded proactive security suite with static analysis, unit test generation, mutation testing, fuzz test generation and PoC generation, running in VS Code and GitHub CI. It is listed as a Circle partner, which puts it directly in front of stablecoin teams. It does not market old-versus-new behaviour diffing.

• Octane

  AI security platform that raised $6.7M, led by Winklevoss Capital and Archetype. A GitHub App analyses every pull request for more than 50 vulnerability classes. It is also a Circle partner and is integrated with Avalanche. It looks for vulnerabilities rather than diffing behaviour.

• Certora AI Composer

  Open-source alpha launched in November 2025 that puts the Certora Prover inside the AI code generation loop, so AI-written Solidity is checked against formal properties before it ships. It is aimed squarely at safe AI-written contracts, but it depends on properties the user writes rather than a reference implementation.

• Recon (Recon Pro / Chimera)

  Cloud invariant testing and fuzzing for EVM contracts, with CI/CD campaigns and AI-generated fuzzing suites (Recon Magic), built on the open-source Chimera framework. Its own figures list clients including Liquity, Centrifuge and Balancer. A team could write differential harnesses on it, and it is also an auditor-side player.

• Nethermind AuditAgent

  AI audit scanner from Nethermind, which is also an audit firm. A GitHub Actions workflow and REST API can fail builds on new critical findings. It is a scanner, not a differential tester.

• Aderyn CI Assistant (Cyfrin)

  A free GitHub Action for static analysis of Solidity in CI, from the audit firm Cyfrin. It is the baseline that buyers already get for free.

• Matterhorn / ASI Alliance

  Announced tools for auditing AI-generated (vibe-coded) blockchain code before deployment, combining automated analysis, human review and testing. I could not confirm that it has shipped.

Checked 2026-10-14