During November 2025, Nathan Levin focused on stabilizing the protocolbuffers/protobuf repository by addressing a critical bug in GPBCodedOutputStream’s size calculation. He reverted a recent branchless varint sizing logic, restoring simpler conditional checks to ensure correct behavior in edge cases and improve downstream compatibility. Working primarily in Objective-C with Cocoa and iOS development skills, Nathan’s targeted rollback enhanced serialization stability and maintainability, reducing the risk of regression and easing future enhancements. His work included automating the reversion of a problematic commit, improving traceability and documentation to support future reviews and ensuring reliable encoding and predictable sizing across varied inputs.