The Ruby 4.0 release is the 30th birthday of the language! Read to understand everything that's changed in Ruby 4, and how to upgrade with the least friction.

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Ruby 4.0 was released on December 25, 2025, marking the language's 30th anniversary. The upgrade is relatively painless with mostly backwards-compatible changes. Key features include Ruby::Box for isolated namespaces within processes, ZJIT as a new method-based JIT compiler alongside YJIT, improvements to Ractors with a new Ractor::Port API, changes to nil splatting behavior, and the ability to start lines with logical operators. Set and Pathname are now built-in core classes, and Array gains new methods like rfind. The article provides a step-by-step upgrade guide covering release notes review, deprecation warnings, testing, bundler updates, and version switching.

Everything you need to know about Ruby 4.0

Logical operators at the beginning of a line in Ruby 4