In February 2026, Josh Gulbronson developed a configurable immutability feature for collection copies in the square/wire repository, focusing on performance optimization for critical application paths. He introduced a wire.make_immutable_copy option in Messages, allowing developers to bypass automatic immutable copies of Lists and Maps when set to false, which reduces memory allocations but requires explicit mutability management. Josh unified this configuration as a Target-level setting, streamlining the API surface and enhancing performance across Kotlin targets. His work leveraged Java, Kotlin, and Protocol Buffers, demonstrating depth in API design and development while addressing the balance between safety and efficiency in software systems.