Bartek Nowotarski developed a major runtime upgrade for the starkware-libs/stwo-cairo repository, focusing on enabling WebAssembly (WASM) support without relying on the Rust standard library. He refined memory address bounds to ensure safer execution in constrained environments and upgraded the cairo-vm dependency to leverage improved performance and security. Bartek also migrated JSON parsing from sonic-rs to serde_json, enhancing serialization reliability and compatibility across components. His work included updating documentation and test coverage to reflect these changes. This feature expanded deployment options for stwo-cairo, demonstrating depth in Rust, dependency management, and serialization within a complex runtime context.