Ruby 4.0 - curated list of resources

Most important links to read about Ruby 4.0 changes

Author

Lucian Ghinda
January 12, 2026

Ruby 4.0 came out on December 25th. If you want to learn about all the new features in Ruby 4.0, here are some resources you should check out.

First, let’s start with the official announcement. I am putting here a screenshot

You can read the entire list of commits between Ruby 3.4 to Ruby 4.0 in Github.

PS: Yes, last year the Ruby official website got a new look. You can read about it here  A New Look for Ruby's Documentation

Don’t get fooled by that screenshot above where is might seem the review is small. Victor is doing an amazing job documeting all those changes. Here is one:

As always Peter Cooper is doing an amazing job identifying the most important pieces that you should know about Ruby 4.0.

Stefan Wintermeyer writes an good analysis providing context for the features in the release, focusing on internal changes, the new JIT compiler, parallelization API, and type system maturity.

Hiroshi Shibata published a list of all the new features that are part of Bundler 4.0 that every Ruby developer should know.

Koichi Sasada (ko1) and Yusuke Endoh (mame) both Ruby core committers go over the changes in Ruby 4.0 and they also provide backstories about the decision process or discussions behind the included changes.

In this article (translated by Koichi Sasada) Yusuke Endoh goes in depth explaining the purpose, intention and future of Ruby::Box.

They end the article with:

“This is a huge contribution opportunity like few in recent years, so please go play with it a lot”

Davide Santangelo (with or without AI) creates here a compilation of multiple resources to give us a nice review of all the important changes in Ruby 4.0

Max Bernstein goes over the improvements in ZJIT happening in the second half of 2025 ending with a graph showing the performance improvements of ZJIT going steadly up:

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