changelog
Jan 29, 2026

Unison 1.1.0 is here

Rebecca Mark

There's a new Unison version in town! This release contains new MCP tools, new IDE features for VS Code users, crucial improvements to existing commands, and much more.

✨ New features

  • The dependents command now works on data constructors and ability request constructors. It used to be that dependents Optional.Some would pull up instances of the type, including Optional.None. This version means you can search by one type variant or another
  • Adds new builtins for Argon2id password hashing. You don’t have to roll your own crypto! Thanks @bbarker
  • New VS Code functionality for "Edit Definition" and "Open on Share" operations
  • New MCP tools: history, reflog, and share-project-info

🔧 Fixes

  • Bytes decoding and comparisons are much faster
  • run myMain arg1 2 3 allows unquoted numbers as arguments
  • run gives a nicer message if the program name is ambiguous
  • branch.diff accepts numbered args and branch hashes
  • Fixed a backwards subtyping check in pattern type checking. (Thanks to @lJoublanc for reporting!)
  • Fixed a pattern-matching bug around duplicate binding names. (Thanks to @jcwilk, @etorreborre , and @gvolpe for reporting!)

🐦‍🔥 Migration notes

This UCM version updates the codebase (not backwards-compatible) to support syncing comments with Unison Share.

🎥 Highlight reel

Here's a demo of some of the features in this release:

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