# Scala 3.10.0-RC1

- Product: Scala (https://whatsnew.fyi/product/scala)
- Vendor: Scala Center
- Date: 2026-09-03
- Version: 3.10.0-RC1
- Original notes: https://github.com/scala/scala3/releases/tag/3.10.0-RC1
- Permalink: https://whatsnew.fyi/product/scala/releases/3.10.0-rc1
- Labels: Pre-release

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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- **changed** — Don't infer implicits from non-accessible companion objects
- **changed** — Enhance constant-folding during inlining
- **changed** — Replace catching StackOverflowError with fuel
- **changed** — Forbid `this` in top-level definitions
- **changed** — Replace runtime.Rich* implicits on primitives by direct extension methods
- **changed** — Make `->` sugar an inline method
- **removed** — Make `with` type operator an error
- **changed** — For bytecode generation, use stock ASM instead of the old scala-asm fork
- **added** — Add support for `\s` space escape in string literals
- **added** — Add support for `//> using dep` directives in the REPL with trailing code
- **added** — Add .deb and .rpm packaging
- **changed** — Enable strictEqualityPatternMatching by default and add deprecation mechanics for `-language` feature flags
- **added** — SIP 61: Unroll default arguments for binary compatibility now in preview
- **added** — SIP 75: Relaxed lambda syntax now in preview
- **added** — SIP 68: Referenceable package objects now in preview
- **added** — Inline Traits & Specialized Traits as experimental feature
- **added** — Modular AGentic Interface Code: Spec strings as experimental feature
- **deprecated** — Deprecate `scala.annotation.strictfp`
- **fixed** — Synthetic cast must not break tailrec optimization
- **changed** — Generate more accurate generic signatures for boxed primitives

##### Breaking changes

- Don't infer implicits from non-accessible companion [#25367](https://github.com/scala/scala3/pull/25367)
- Enhance constant-folding during inlining [#25731](https://github.com/scala/scala3/pull/25731)
- Replace catching StackOverflowError with fuel [#25937](https://github.com/scala/scala3/pull/25937)
- Forbid `this` in top-level definitions [#26448](https://github.com/scala/scala3/pull/26448)
- Replace runtime.Rich* implicits on primitives by direct extension methods. [#23872](https://github.com/scala/scala3/pull/23872)
- Make `->` sugar an inline method [#24728](https://github.com/scala/scala3/pull/24728)
- Make `with` type operator an error [#26545](https://github.com/scala/scala3/pull/26545)
- For bytecode generation, use stock ASM (not our old scala-asm fork) [#26772](https://github.com/scala/scala3/pull/26772)


#### Highlights of the release

- Add support for `\s` space escape [#26515](https://github.com/scala/scala3/pull/26515)
- Add support for `//> using dep` directives in the REPL (along with trailing code) [#26507](https://github.com/scala/scala3/pull/26507)
- Add .deb and .rpm packaging [#26858](https://github.com/scala/scala3/pull/26858)
- New stablized features:
    - SIP 71: strictEqualityPatternMatching is now enabled by default default & add deprecation mechanics for `-language` feature flags [#26424](https://github.com/scala/scala3/pull/26424)
- New preview features:
    - SIP 61: Unroll default arguments for binary compatibliy is now in preview [#24903](https://github.com/scala/scala3/pull/24903)
    - SIP 75: Relaxed lambda syntax is now in preview [#26728](https://github.com/scala/scala3/pull/26728)
    - SIP 68: Referenceable package objects is now preview [#24586](https://github.com/scala/scala3/pull/24586)
- New experimental features:
    - Pre-SIP: Inline Traits & Specialized Traits [#26156](https://github.com/scala/scala3/pull/26156)
    - Pre-SIP: Modular AGentic Interface Code: Spec strings [#26486](https://github.com/scala/scala3/pull/26486)

#### Other changes and fixes

##### Annotations

- Add regression test for Java annotation @Retention visibility (#389) [#26339](https://github.com/scala/scala3/pull/26339)
- Synthetic cast must not break tailrec [#26343](https://github.com/scala/scala3/pull/26343)
- Deprecate `scala.annotation.strictfp` [#24839](https://github.com/scala/scala3/pull/24839)

##### Backend

- More accurate generic signatures for boxed primitives [#25944](https://github.com/scala/scala3/pull/25944)
- Do not emit unnecessary fields for nested objects [#25538](https://github.com/scala/scala3/pull/25538)
- For bytecode generation, use stock ASM (not our old scala-asm fork) [#25989](https://github.com/scala/scala3/pull/25989)
- Layer JVM backend without cycles [#26237](https://github.com/scala/scala3/pull/26237)

##### Desugaring

- Use updated params when desugaring macro context bounds [#26206](https://github.com/scala/scala3/pull/26206)

##### Scaladoc

- Scaladoc: find members ending in `!` or `$` [#26739](https://github.com/scala/scala3/pull/26739)
- Scaladoc: Do not crash on class+module in API package [#26766](https://github.com/scala/scala3/pull/26766)
- Scaladoc: Do not allow resolving warnings to hide each other [#26742](https://github.com/scala/scala3/pull/26742)
- Scaladoc: Recursively unwrap exported trees [#26737](https://github.com/scala/scala3/pull/26737)
- Scaladoc: Stop hijacking link clicks [#26664](https://github.com/scala/scala3/pull/26664)
- Scaladoc: stay on the same page when switching versions [#26762](https://github.com/scala/scala3/pull/26762)
- Disable bogus Scaladoc warnings [#26663](https://github.com/scala/scala3/pull/26663)

##### Documentation

- Drop: remove access to `Predef.any2stringadd` [#24656](https://github.com/scala/scala3/pull/24656)
- Fixes to `into` doc [#26203](https://github.com/scala/scala3/pull/26203)
- Fix markdown code fences in PartialFunction.sca

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