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Crystal 1.5.1 is released!

We are releasing the first patch release of the 1.5 series.

Pre-built packages are available on GitHub Releases and our official distribution channels. See for installation instructions.


In this patch release we included 13 PRs since the 1.5.0 release by 7 contributors. We thank all the effort put into improving the language! ❤️

Remarkable changes

A regression introduced in 1.5.0 prevented the typechecker to correctly infer the type of a union of a splat of types (something of the form Union(*T)). This is now fixed.

To illustrate, the following code typechecks in 1.4.1 but not in 1.5.0.

class Foo(*T)
  @value : Union(*T)
  def initialize(@value)

p Foo(Int32, String).new(3), Foo(Int32, String).new("")

For more details of this and other bug fixes included in this release, please visit the changelog.


We have been able to do all of this thanks to the continued support of 84codes, Nikola Motor Company and every other sponsor. To maintain and increase the development pace, donations and sponsorships are essential. OpenCollective is available for that.

Reach out to if you’d like to become a direct sponsor or find other ways to support Crystal. We thank you in advance!