Teaching Claude Code to Upgrade Rails (Artificial Ruby NYC, March, 2026)

Presented at Artificial Ruby NYC on March 25th, 2026.

For more than 8 years, we've been upgrading Rails applications at FastRuby.io. More than 60,000 developer-hours going from Rails 2.3 all the way to 8.1. Along the way, we've learned what
works and what doesn't — and we've seen what happens when teams skip versions or ignore deprecation warnings.

Claude Code is great at general coding tasks, but on its own, it doesn't know that dual booting is worth the effort. It doesn't know that you should address deprecation warnings before you
upgrade. It doesn't know that your load_defaults should match your version of Rails. Without that structure, even the most capable AI will take shortcuts that create problems down the road.

So we encoded our methodology into three open-source Claude Code skills:

- Rails Upgrade Skill — enforces sequential upgrades and generates codebase-specific migration reports: https://github.com/ombulabs/claude-code_rails-upgrade-skill
- Dual Boot Skill — sets up next_rails so you can run your test suite against both Rails versions locally, in CI, and eventually in production:
https://github.com/ombulabs/claude-code_dual-boot-skill
- Rails Load Defaults Skill — walks through each new_framework_defaults config one at a time until your load_defaults matches your Rails version:
https://github.com/ombulabs/claude-code_rails-load-defaults-skill

In this talk I cover why generic AI falls short for complex upgrades, the opinionated decisions we baked into each skill, and then I do a live demo showing how the three skills work
together.

If you want to give it a try: https://github.com/ombulabs/claude-code_rails-upgrade-skill

Blog post with more details: https://www.fastruby.io/blog/open-source-claude-code-skill-for-rails-upgrades.html

Transcript

1. Teaching Claude Code to Upgrade Rails Artificial Ruby NYC March 25th, 2026
2. What if we could put Ruby on Rails upgrades on autopilot?
3. What if we could implement a repeatable upgrade process using Claude Code?
4. /rails_upgrade Upgrade from Rails 7.1 to Rails 7.2
5. Demo: An opinionated Code Code skill to upgrade Rails*
6. * Upgrade Rails the FastRuby.io way
7. FastRuby.io: More than 60,000 dev/hours upgrading Rails 🚀
11. UPGRADE RAILS
12. 🤖 AI-enhanced Roadmap fastruby.io/ automated- roadmap
14. What’s a Claude Code skill?
15. Can you combine skills? Yes! Rails Upgrade Skill depends on Load Defaults Skill and Dual Boot Skill
16. Why do I need a skill? Claude Code is great at general coding tasks, but it doesn’t have a ton of experience doing upgrades for huge monoliths…
17. Process 1 bundle exec rake test 2 Track Deprecation Warnings 3 Address Deprecation Warnings 4 next bundle install 5 next bundle exec rake test 6 Fix Errors & Failures 7 Deploy to Staging 8 QA / Rework 9 Gradually Deploy to Production 10 Monitor
18. https://github.com/ombulabs/ claude-code_rails-upgrade-skill
19. Strong Opinions, Strongly Held
20. No test suite? “NO UPGRADE FOR YOU”
21. Strong arm Claude Code into dual booting all the things
22. Dual boot locally, in CI, and eventually in production
23. Match your load_defaults with your version of Rails
24. From Rails 2.3 to Rails 8.1 and beyond…
25. <DEMO TIME>
26. Next Steps • Better workflow for slow tests (rspec spec/models maybe?) • When running the test suite for first time, keep track of deprecation warnings • Address deprecation warnings before dual boot • Some sort of eval system for maintainability and quality control
27. Give it a try and report back any issues you find on GitHub or Discord ♥ 27
28. https://github.com/ ombulabs/ claude-code_rails-upgrade-skill
29. 29 Thank you!
30. Questions? 30