# Scala 3.9.0-RC1

- Product: Scala (https://whatsnew.fyi/product/scala)
- Vendor: Scala Center
- Date: 2026-06-10
- Version: 3.9.0-RC1
- Original notes: https://github.com/scala/scala3/releases/tag/3.9.0-RC1
- Permalink: https://whatsnew.fyi/product/scala/releases/3.9.0-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'.

---

- **added** — Support expectations in snippets in Scaladoc
- **changed** — Make `into` type and modifier stable
- **changed** — Unify annotation handling for thread-safe and -unsafe lazy vals
- **changed** — Emit acceptable Java generic signatures for higher-kinded types
- **changed** — Unwrap refined types for Java generic signatures
- **changed** — Emit nested module classes as static inner classes
- **fixed** — Use `IndexOutOfBoundsException` constructor with `Int`
- **fixed** — Fix Java signatures for arrays of value classes
- **fixed** — Fix Java generic signatures for context functions
- **fixed** — Handle HKT bounds in Java generic signatures
- **fixed** — Lambda-owned param ref in constructor incurs no field
- **fixed** — Fix Scoverage and separation checking failures
- **fixed** — Scoverage: do not instrument methods that have too large bodies
- **fixed** — Scoverage & CC interaction: exempt CC nested symbols from @experimental check
- **fixed** — Fix Coverage + Experimental nested match cases interaction
- **fixed** — Scoverage: fix broken warnings related to tail recursion and infinite loop detection
- **fixed** — Scoverage: correctly detect curried constructor applications
- **fixed** — Scoverage: correctly lift wildcard and singleton types
- **removed** — Remove automatic collection of entry points
- **fixed** — Restore `Automatic-Module-Name` in standard library's manifest

#### Highlights of the release

- [Long Term Support](https://www.scala-lang.org/blog/2022/08/17/long-term-compatibility-plans.html)
- Make `into` type and modifier stable [#26184](https://github.com/scala/scala3/pull/26184)
- Remove automatic collection of entry points [#25215](https://github.com/scala/scala3/pull/25215)
- Scaladoc: support expectations in snippets [#25713](https://github.com/scala/scala3/pull/25713)
- Restore `Automatic-Module-Name` in standard library's manifest [#26218](https://github.com/scala/scala3/pull/26218)

#### Other changes and fixes

##### Annotations

- Unify annotation handling for thread-safe & -unsafe lazy vals [#24907](https://github.com/scala/scala3/pull/24907)

##### Backend

- Use `IndexOutOfBoundsException` constructor with `Int` [#24764](https://github.com/scala/scala3/pull/24764)
- Emit acceptable Java generic signatures for HKTs [#25540](https://github.com/scala/scala3/pull/25540)
- Unwrap refined types for Java generic signatures [#25626](https://github.com/scala/scala3/pull/25626)
- Fix Java signatures for arrays of value classes [#25631](https://github.com/scala/scala3/pull/25631)
- Fix Java generic signatures for context functions [#25632](https://github.com/scala/scala3/pull/25632)
- Handle HKT bounds in Java generic signatures [#25744](https://github.com/scala/scala3/pull/25744)
- Emit nested module classes as static inner classes [#26137](https://github.com/scala/scala3/pull/26137)
##### Constructors

- Lambda-owned param ref in ctor incurs no field [#23286](https://github.com/scala/scala3/pull/23286)

##### Coverage

- Fix #25624: Scoverage and separation checking failures [#25625](https://github.com/scala/scala3/pull/25625)
- Scoverage: do not instrument methods that have too large bodies [#25629](https://github.com/scala/scala3/pull/25629)
- Scoverage & CC interaction: exempt CC nested symbols from @experimental check [#25687](https://github.com/scala/scala3/pull/25687)
- Coverage + Experimental nested match cases interaction fix [#25913](https://github.com/scala/scala3/pull/25913)
- Scoverage: fix broken warnings related to tail recursion and infinite loop detection [#25941](https://github.com/scala/scala3/pull/25941)
- Scoverage: correctly detect curried constructor applications [#26048](https://github.com/scala/scala3/pull/26048)
- Scoverage: correctly lift wildcard and singleton types [#26049](https://github.com/scala/scala3/pull/26049)
- Scoverage: refrain from lifting closures for capture calculus compatibility [#26067](https://github.com/scala/scala3/pull/26067)
- Scoverage: fix lifted type computation for parameterless methods [#26069](https://github.com/scala/scala3/pull/26069)
- Scoverage: Fix coverage parameterless select qualifier casts [#26087](https://github.com/scala/scala3/pull/26087)

##### Documentation

- Sys, concurrent, runtime (1): fill in missing @param, @tparam, and @return tags in Scaladoc comments [#25371](https://github.com/scala/scala3/pull/25371)
- Collection mutable (2): fill in missing @param, @tparam, and @return tags in Scaladoc comments [#25372](https://github.com/scala/scala3/pull/25372)
- Collection immutable (3): fill in missing @param, @tparam, and @return tags in Scaladoc comments [#25373](https://github.com/scala/scala3/pull/25373)
- Collection core (4): fill in missing @param, @tparam, and @return tags in Scaladoc comments [#25374](https://github.com/scala/scala3/pull/25374)
- Numeric types (5): fill in missing @param, @tparam, and @return tags in Scaladoc comments [#25375](https://github.com/scala/scala3/pull/25375)
- Array, IArray, Predef, Option (6): fill in missing @param, @tparam, and @return tags in Scaladoc comments [#25376](https://github.com/scala/scala3/pull/25376)
- Math (7): fill in missing @param, @tparam, and @return tags in Scaladoc comments [#25377](https://github.com/scala/scala3/pull/25377)
- Quoted, compiletime (8): fill in missing @param, @tparam, and @return tags in

_[Truncated at 4000 characters — full notes: https://github.com/scala/scala3/releases/tag/3.9.0-RC1]_