Oct 15, 2026wkelyson
Upgrading from Ruby 3.4.4 to Ruby 4.0.3: a step-by-step guide for Rails apps
Ruby 4.0 is the first major version bump in over a decade, but most of the work is under the hood. Here is what actually breaks when moving a Rails app from 3.4.4 to 4.0.3, what you gain, and a phased upgrade plan you can run in a week.