Migrating Mojo Libraries from 25.7 to 26.1

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Just in time for the February 2026 Community meeting :wink: I’ve just finished migrating five open-source Mojo libraries from 0.25.7 to 0.26.1:

They’re all “plain and simple Mojo” libraries (no MAX usage), but they do rely on the same underlying toolchain and channels, so the 0.26.1 release still meant a fair bit of work.

I wrote up a detailed article here:

:backhand_index_pointing_right: Migrating Mojo Libraries from 25.7 to 26.1 🔥: Lessons from updating my mojo-packages

The post covers:

  • How I standardised toolchain versions across all projects (max = ">=26.1.0,<27" and mojo_version = "=0.26.1" in the recipes)
  • What changed around string/indexing semantics and how I moved lexers and parsers over to codepoint_slices() and explicit List[String] buffers
  • Why I’m aiming for “zero compiler warnings” on 26.1 to make future upgrades easier
  • How I wired the pixi + pre-submit workflow to run all Mojo tests, examples, recipe validation, rattler-build, and a basic install smoke test
  • A few case studies (mojo-dotenv, mojo-ini, mojo-toml, mojo-asciichart) and some benchmark before/after numbers

If you’re maintaining your own Mojo libraries or playing with text-heavy code in 26.1, I’d be interested in what you’re running into and whether there are better patterns we can share around string handling, error reporting, or benchmarking.

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Great summary, thank you for sharing this Michael. This is very helpful to understand the aggregate impact of changes being made to the language and libraries.