# Scala 3.9.0 — 3.9.0 LTS

- Product: Scala (https://whatsnew.fyi/product/scala)
- Vendor: Scala Center
- Date: 2026-09-03
- Version: 3.9.0
- Original notes: https://github.com/scala/scala3/releases/tag/3.9.0
- Permalink: https://whatsnew.fyi/product/scala/releases/3.9.0

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** — SIP-71 - Allow fully implicit conversions in Scala 3 with `into` is now stable
- **added** — Scaladoc support for expectations in snippets
- **changed** — Remove automatic collection of entry points
- **changed** — Restore `Automatic-Module-Name` in standard library's manifest
- **changed** — Migrate Scala CLI's using directive parser to a compiler module
- **changed** — Upgrade to Scala.js 1.22.0 with stable WebAssembly backend, sbt 2.x support, and WebAssembly configuration
- **changed** — Bump Scala CLI to v1.16.0 with JShell support in repl, JUnit 5 support, SBT 2.x exports, WebAssembly support, and Sloth support for patching lazy vals on JDK 24+
- **fixed** — Unify annotation handling for thread-safe and unsafe lazy vals
- **fixed** — Ignore `@throws` annotation on non-methods
- **fixed** — Use `IndexOutOfBoundsException` constructor with `Int`
- **fixed** — Emit acceptable Java generic signatures for HKTs
- **fixed** — Unwrap refined types for Java generic signatures
- **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** — Emit nested module classes as static inner classes
- **fixed** — Emit inline info attribute
- **fixed** — Box bounded arguments of HKT result types in Java generic signatures
- **fixed** — Scoverage and separation checking failures

#### Highlights of the release

- [Long Term Support](https://www.scala-lang.org/blog/2022/08/17/long-term-compatibility-plans.html)
- SIP-71 - Allow fully implicit conversions in Scala 3 with `into` is now 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)
- Migrate Scala CLI's using directive parser to a compiler module [#26449](https://github.com/scala/scala3/pull/26449)
- Upgrade to Scala.js 1.22.0. [#26389](https://github.com/scala/scala3/pull/26389)
    * Stable WebAssembly backend
    * sbt 2.x support
    * Configuration for WebAssembly
    * Refer to [Scala.js v1.22 release notes](https://www.scala-js.org/news/2026/06/20/announcing-scalajs-1.22.0/) for details
- Bump Scala CLI to v1.16.0 [#26703](https://github.com/scala/scala3/pull/26703):
    * JShell support in repl
    * JUnit 5 (Jupiter) support
    * SBT 2.x exports
    * Dropped Ammonite support
    * WebAssembly support (experimental)
    * Sloth support - patch Scala 3.0-3.7 lazy vals on classpath using `sun.misc.Unsafe` to JDK 24+ compatible implementation  (experimental)
    * Refer to Scala CLI [v1.15.0](https://github.com/VirtusLab/scala-cli/releases#release-v1.15.0) and [v1.16.0](https://github.com/VirtusLab/scala-cli/releases#release-v1.16.0) for details

#### Other changes and fixes

##### Annotations

- Unify annotation handling for thread-safe & -unsafe lazy vals [#24907](https://github.com/scala/scala3/pull/24907)
- Ignore `@throws` annotation on non-methods [#26802](https://github.com/scala/scala3/pull/26802)

##### JVM 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)
- Don't skip generic signature for constructors with generic `using` parameters [#26302](https://github.com/scala/scala3/pull/26302)
- Fix generic signature of trait val setter [#26374](https://github.com/scala/scala3/pull/26374)
- Reliably decide whether to generate static forwarders [#26510](https://github.com/scala/scala3/pull/26510)
- Fix generic signatures for inherited inner classes [#26549](https://github.com/scala/scala3/pull/26549)
- Fix regression #26374: generic signatures of mixed-in trait setters [#26542](https://github.com/scala/scala3/pull/26542)
- Fix regression #26550: revert isPrimitiveValueType change [#26565](https://github.com/scala/scala3/pull/26565)
- Emit inline info attribute [#26650](https://github.com/scala/scala3/pull/26650)
- Stop hiding errors in `GenericSignatureVisitor` [#26632](https://github.com/scala/scala3/pull/26632)
- Emit a super init call for primitives on the JVM [#26630](https://github.com/scala/scala3/pull/26630)
- Box bounded arguments of HKT result types in Java generic signatures [#26787](https://github.com/scala/scala3/pull/26787)
- Fix issue with reading legal java cyclic signatures [#26775](https://github.com/scala/scala3/pull/26775)
- Do not emit Java generic signatures for trait private val setters [#26633](https://github.com/scala/scala3/pull/26633)

##### Constructors

- Lambda-owned

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