OCaml 5.5.0 released

Category: Languages
Status: confirmed
Sources: OCaml 5.5.0 release notes, release announcement, r/programming
Summary: OCaml 5.5.0 shipped on 2026-06-19. Language additions include module-dependent functions (modular explicits, a lightweight functor form letting a function take a module argument), polymorphic function parameters, and extended local definitions (let module, let exception, let open usable in most structure items). Runtime and compiler work includes a relocatable compiler, dropping the Winpthreads dependency on Windows in favor of WinAPI directly, garbage-collector idle-phase and generational-stack-scanning improvements, and roughly 60 new standard-library functions. The release carries multiple breaking changes to type-system handling.
Why it matters: Module-dependent functions reduce the need for full functors for common module-passing patterns, and the relocatable compiler and Windows changes ease toolchain packaging.
Follow-up: Watch for opam ecosystem updates against the 5.5 breaking changes.