Yukihiro “Matz” Matsumoto

Yukihiro Matsumoto (born 1965 in Osaka), universally known as Matz, released the Ruby programming language in 1995 with a philosophy that made him beloved among developers: languages should be designed for human happiness. Ruby went on to power much of the modern web through Rails, and Matz has remained its chief designer for three decades.

Spinel: a compiler co-authored by Claude

At RubyKaigi 2026 in Hakodate, Matz unveiled Spinel, an ahead-of-time native compiler for Ruby that he had conceived three years earlier but only now built — in a matter of weeks, working with Anthropic’s Claude Code, with most files in the repository marked “co-authored by: Claude.” In his tests, Spinel-compiled code ran roughly 11.6 times faster than a stripped-down Ruby build, and the project went through three complete rewrites at accelerating speed.

The keynote traced a personal conversion. At RubyKaigi 2025 Matz had said humans should be primary and AI subservient; a year later, per Gihyo’s conference report, he described the relationship as having become a partnership — recounting how a Karatsuba-multiplication implementation that defeated a month of AI-assisted effort in 2024 took shape in fifteen minutes with Claude Code in 2026. He even imposed the constraint of building Spinel without a code editor, directing the AI entirely.

Observers noted the caveats alongside the wonder: Spinel supports only a subset of Ruby, and reviewers found that code which compiles is not necessarily code which works. But as a demonstration of what a master language designer can now build in weeks instead of years, the talk was received as a landmark in what AI-assisted systems programming can be.