# Crystal 1.21.0

- Product: Crystal (https://whatsnew.fyi/product/crystal)
- Vendor: Crystal Language
- Date: 2026-07-16
- Version: 1.21.0
- Original notes: https://github.com/crystal-lang/crystal/releases/tag/1.21.0
- Permalink: https://whatsnew.fyi/product/crystal/releases/1.21.0

What's New is an index, not a publisher: every entry below links to the vendor's own release notes, which are the authoritative source. Entries are labelled where they are hand-curated sample data, pre-releases, or drawn from a secondary source such as a developer blog.

Reuse: the summaries, labels and curation here are © What's New. Quote freely with attribution and a link back; wholesale republication of the corpus is not permitted — terms: https://whatsnew.fyi/terms. The vendors' own release notes remain their publishers'.

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- **removed** — Disable automatic fallback to legacy PCRE
- **changed** — Release Execution Contexts
- **added** — Add %W percent string array literals with interpolation
- **added** — Add TypeNode#all_methods that includes the type's ancestor's methods
- **added** — Align long-only options in OptionParser help
- **added** — Make Channel(T) an Iterator(T)
- **added** — Add support for OpenSSL 4.0
- **added** — Support OpenSSL 4.x DLLs on Windows MSVC
- **added** — Add Socket#sendfile (and Crystal::EventLoop::Socket#sendfile)
- **added** — Add HTTP::WebSocket#receive as a synchronous call
- **added** — Add Crystal::EventLoop::FileDescriptor#pread
- **added** — Add without_main flag
- **changed** — OpenBSD: use kqueue event loop by default
- **added** — Support nested root properties in JSON::Field
- **added** — Add URI::Params::Field(ignore:), ignore_serialize, ignore_deserialize
- **added** — Allow chaining #should, #should_not expectations
- **added** — Expose Path#kind
- **added** — Add splat overloads for Process.capture, .run and .new
- **added** — Add Process::Status.[] constructor
- **added** — Add String#present?
- **added** — Add UUID.v6 and .v8 generators

###### Breaking changes

###### stdlib

- _(runtime)_ Release: Execution Contexts ([#17100], [#17104], thanks @ysbaddaden)
- _(text)_ Disable automatic fallback to legacy `PCRE` ([#16924], thanks @straight-shoota)

[#16924]: https://github.com/crystal-lang/crystal/pull/16924
[#17100]: https://github.com/crystal-lang/crystal/pull/17100
[#17104]: https://github.com/crystal-lang/crystal/pull/17104

###### Features

###### lang

- Add `%W` percent string array literals with interpolation ([#16919], thanks @straight-shoota)
- _(macros)_ Add `TypeNode#all_methods` that includes the type's ancestor's methods ([#16902], thanks @Blacksmoke16)

[#16902]: https://github.com/crystal-lang/crystal/pull/16902
[#16919]: https://github.com/crystal-lang/crystal/pull/16919

###### stdlib

- _(cli)_ Align long-only options in OptionParser help ([#16914], thanks @kojix2)
- _(collection)_ Make `Channel(T)` an `Iterator(T)` ([#16916], thanks @jgaskins)
- _(crypto)_ Add support for OpenSSL 4.0 ([#16839], thanks @straight-shoota)
- _(crypto)_ Support OpenSSL 4.x DLLs on Windows MSVC ([#17116], thanks @HertzDevil)
- _(networking)_ **[experimental]** Add `Socket#sendfile` (and `Crystal::EventLoop::Socket#sendfile`) ([#16665], [#17133], thanks @ysbaddaden, @straight-shoota)
- _(networking)_ Add `HTTP::WebSocket#receive` as a synchronous call ([#16689], thanks @jgaskins)
- _(runtime)_ Add `Crystal::EventLoop::FileDescriptor#pread` ([#17068], thanks @ysbaddaden)
- _(runtime)_ Add `without_main` flag ([#17074], thanks @kojix2)
- _(runtime)_ OpenBSD: use kqueue event loop by default ([#17123], thanks @ysbaddaden)
- _(serialization)_ Support nested `root` properties in `JSON::Field` ([#17016], thanks @tcoatswo)
- _(serialization)_ Add `URI::Params::Field(ignore:)`, `ignore_serialize`, `ignore_deserialize` ([#17029], thanks @trypsynth)
- _(specs)_ Allow chaining `#should`, `#should_not` expectations ([#17020], thanks @straight-shoota)
- _(system)_ Expose `Path#kind` ([#16917], thanks @Sija)
- _(system)_ Add splat overloads for `Process.capture`, `.run` and `.new` ([#16975], thanks @straight-shoota)
- _(system)_ Add `Process::Status.[]` constructor ([#17003], thanks @straight-shoota)
- _(text)_ Add `String#present?` ([#16930], thanks @Sija)
- _(text)_ Add `UUID.v6` and `.v8` generators ([#17010], thanks @trypsynth)

[#16665]: https://github.com/crystal-lang/crystal/pull/16665
[#16689]: https://github.com/crystal-lang/crystal/pull/16689
[#16839]: https://github.com/crystal-lang/crystal/pull/16839
[#16914]: https://github.com/crystal-lang/crystal/pull/16914
[#16916]: https://github.com/crystal-lang/crystal/pull/16916
[#16917]: https://github.com/crystal-lang/crystal/pull/16917
[#16930]: https://github.com/crystal-lang/crystal/pull/16930
[#16975]: https://github.com/crystal-lang/crystal/pull/16975
[#17003]: https://github.com/crystal-lang/crystal/pull/17003
[#17010]: https://github.com/crystal-lang/crystal/pull/17010
[#17016]: https://github.com/crystal-lang/crystal/pull/17016
[#17020]: https://github.com/crystal-lang/crystal/pull/17020
[#17029]: https://github.com/crystal-lang/crystal/pull/17029
[#17068]: https://github.com/crystal-lang/crystal/pull/17068
[#17074]: https://github.com/crystal-lang/crystal/pull/17074
[#17116]: https://github.com/crystal-lang/crystal/pull/17116
[#17123]: https://github.com/crystal-lang/crystal/pull/17123
[#17133]: https://github.com/crystal-lang/crystal/pull/17133

###### compiler

- _(cli)_ Classify compiler exit reasons ([#17028], thanks @straight-shoota)
- _(debugger)_ Improve proc debug metadata ([#16830], thanks @skuznetsov)
- _(debugger)_ Emit debug metadata for constants and class vars ([#16831], thanks @skuznetsov)
- _(debugger)_ Improve LLDB collection formatters ([#16832], thanks @skuznetsov)
- _(parser)_ Add `ASTNode#inspect` ([#16699], thanks @straight-shoota)
- _(parser)_ Parse `MacroVar` with empty expressions: `%var{}` ([#16772], thanks @straight-shoot

_[Truncated at 4000 characters — full notes: https://github.com/crystal-lang/crystal/releases/tag/1.21.0]_