What's new in Ruby 4.0

kept by eddie dec 19, 25

Ruby 4.0 ships Christmas 2025 with a new ZJIT compiler, redesigned Ractor ports, experimental isolated namespaces via Ruby::Box, and faster object allocations.

Ruby 4.0.0 Released
Ruby 4.0.0 introduces experimental Ruby Box for isolated definitions and ZJIT, a new JIT compiler built in Rust, alongside Ractor improvements and core class updates.
also on ZJIT, Ruby, #programming-languages
Ruby 4.0.0 Preview2
Ruby 4.0.0 preview2 introduces Unicode 17.0 support, an experimental ZJIT compiler, and language changes like `*nil` no longer calling `nil.to_a`.
also on YJIT, Ruby, #programming-languages
Story - NERD
NERD is a programming language optimized for LLM tokenization, reducing tokens by 50-70% compared to TypeScript, designed for AI-authored code.
also on #compiler, #programming-languages
mostlyobvio.us — Curiosity reduced the heap size by 60%
By modifying OpenTelemetry's AWS SDK instrumentation to skip autoloaded services, the author cut Ruby heap usage from 163.8 MB to 67.1 MB, a ~60% reduction.
also on Ruby, #performance, #software-engineering
RubyKaigi 2026 - RubyKaigi 2026
RubyKaigi 2026 was held April 22-24 at Hakodate Arena and Citizen Hall in Hokkaido, Japan, with keynotes from Matz, Charles Nutter, and Satoshi Tagomori.
also on Ruby, #programming-languages