# Racket v9.0 — Racket v9.0

- Product: Racket (https://whatsnew.fyi/product/racket)
- Vendor: Racket
- Date: 2025-11-23
- Version: v9.0
- Original notes: https://github.com/racket/racket/releases/tag/v9.0
- Permalink: https://whatsnew.fyi/product/racket/releases/v9.0

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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- **added** — Racket supports parallel threads that can be created using the `#:pool` argument to thread creation
- **added** — Threads created with `#:keep` set to `'results` will record their results for later retrieval with `thread-wait`
- **added** — The `black-box` wrapper prevents the optimizing compiler from optimizing away certain computations entirely
- **added** — The `decompile-linklet` function can map linklets back to s-expressions
- **added** — Distribute natipkg packages for AArch64 useful for package-build and package-testing infrastructure
- **added** — The `math` library includes Weibull distributions
- **changed** — When using BC Racket, the `processor-count` function is changed to always return the parallel count
- **changed** — Check Syntax tracks identifiers more deeply nested in the origin field of syntax objects
- **fixed** — Many repairs and documentation improvements

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- Racket supports parallel threads. For more information see the new
  blog post on the topic.
    - Parallel threads can be created using the `#:pool` argument to
      thread creation.
    - Threads created with `#:keep` set to `'results` will record their
      results for later retrieval with `thread-wait`.
- The `black-box` wrapper prevents the optimizing compiler from
  optimizing away certain computations entirely. This can be helpful
  in ensuring that benchmarks are accurate.
- The `decompile-linklet` function can map linklets back to
  s-expressions.
- When using BC Racket, the `processor-count` function is changed to
  always return the parallel count.
- We now distribute "natipkg" packages for AArch64, useful for
  package-build and package-testing infrastructure.
- Check Syntax tracks identifiers more deeply nested in the "origin"
  field of syntax objects.
- The `math` library includes Weibull distributions.
- There are many other repairs and documentation improvements!

The following people contributed to this release:

Alexander Shopov, Anthony Carrico, Bert De Ketelaere, Bogdan Popa,
Cadence Ember, David Van Horn, Gustavo Massaccesi, Jade Sailor,
Jakub Zalewski, Jens Axel Søgaard, jestarray, John Clements, Jordan
Johnson, Matthew Flatt, Matthias Felleisen, Mike Sperber, Philip
McGrath, RMOlive, Robby Findler, Ruifeng Xie, Ryan Culpepper, Sam
Phillips, Sam Tobin-Hochstadt, Sebastian Rakel, shenleban tongying,
Shu-Hung You, Stephen De Gabrielle, Steve Byan, and Wing Hei Chan.

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