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Rails Drops 6.1 Marshal Format, Modernizes Rack Guide

By RepoJournal · Filed · About Rails

Rails is removing support for the 6.1 Active Record Marshal format to unlock faster evolution of internal object representation without compatibility constraints.

The Rails core team merged the decision to stop deserializing Rails 6.1 serialized records [2], a breaking change that simplifies the codebase and removes a maintenance burden that was blocking architectural improvements to Active Record's Attribute and AttributeSet internals [3]. This won't affect most applications since serialized records from that era are rare in production, but if you're still passing Marshal data between process boundaries, plan a migration away from that pattern before upgrading to the next major release. On the documentation front, Rails shipped a comprehensive overhaul of the Rack guide [1], adding sections on custom middleware integration and advanced Rack API usage alongside clarifications on the default middleware stack. The guide restructure aligns Rails documentation with the Configuration guide format, making it easier to navigate. A separate fix ensures Active Record attachment changes survive STI class conversions [4], addressing a longstanding bug where metadata would be silently lost during polymorphic record transformations.

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Action items

References

  1. [1] [RF-Docs] [ci-skip] Update the Rails on Rack guide ↗ rails/rails
  2. [2] Remove support for Rails 6.1 Active Record Marshal format rails/rails
  3. [3] Merge pull request #57382 from byroot/remove-ar-marshal-6.1 rails/rails
  4. [4] Preserve attachment changes when converting record to another class using STI ↗ rails/rails

Quick answers

What shipped in Rails on May 19, 2026?
Rails is removing support for the 6.1 Active Record Marshal format to unlock faster evolution of internal object representation without compatibility constraints. In total, 15 commits and 9 pull requests landed.
Who contributed to Rails on May 19, 2026?
2 developers shipped this update, including ayushn21 and fatkodima.
What were the notable Rails updates?
[RF-Docs] [ci-skip] Update the Rails on Rack guide, Remove support for Rails 6.1 Active Record Marshal format, and Merge pull request #57382 from byroot/remove-ar-marshal-6.1.

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