Sergey Pepyakin worked on the IrreducibleOSS/binius and binius64 repositories, focusing on core circuit design and cryptographic verification in Rust. He delivered a comprehensive refactor of the binius64 codebase, modernizing build and test workflows, clarifying component naming, and optimizing performance through improved index handling and build configuration. Sergey expanded test coverage for arithmetic gadgets and cryptographic primitives, including robust edge-case validation for unsigned 32-bit addition and SHA256 circuits. His work emphasized maintainability and reliability, addressing bugs and enhancing documentation. By leveraging Rust, TOML, and version control, Sergey improved project structure and ensured the cryptographic circuits were release-ready and robust.