diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index a5149ce..0da2e5c 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -36,7 +36,7 @@ jobs:
 
       - uses: oven-sh/setup-bun@v2
         with:
-          bun-version: 1.4.0
+          bun-version: 1.4.1
 
       - name: Check formatting
         run: $MILL --no-server mill.scalalib.scalafmt.ScalafmtModule/checkFormatAll __.sources
diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index f84f2aa..23df177 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -31,7 +31,7 @@ jobs:
       - name: Set up Bun
         uses: oven-sh/setup-bun@v2
         with:
-          bun-version: 1.4.0
+          bun-version: 1.4.1
 
       - name: Cache Coursier
         uses: actions/cache@v4
diff --git a/.mill-version b/.mill-version
index e25d8d9..18efdb9 100644
--- a/.mill-version
+++ b/.mill-version
@@ -1 +1 @@
-1.1.5
+1.1.8
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 40c801f..9417454 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,29 @@ All notable changes to `mill-bun-plugin` will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [0.3.1] - Scala 3.9.0 LTS validation, Mill 1.1.8 (2026-09-04)
+
+### Changed
+
+- Every Scala.js integration fixture, `example-scalajs`, `examples`, and the README snippets now
+  build with **Scala 3.9.0 LTS** on Scala.js 1.22.0. Scala 3.9.0 emits Scala.js 1.22 IR, which the
+  linker bundled by Mill 1.1.x's `ScalaJSConfigModule` (IR ≤ 1.20) rejects; the explicit
+  `scalaJSVersion` route introduced in 0.3.0 is the supported way to build Scala 3.9 code, and the
+  suite now proves that exact combination.
+- The plugin builds and runs its unit, integration, and example suites on **Mill 1.1.8**:
+  `.mill-version`, the launcher defaults, every fixture/example `//| mill-version` header, and —
+  the part that actually decides which Mill the fixtures run in-process — `mill-testkit` is now
+  pinned separately (`millTestkitVersion = "1.1.8"`). The compile target stays at Mill 1.1.5, so
+  the supported floor is unchanged and the jar under test is the real consumer shape.
+- The plugin's own `scalaVersion` stays at 3.8.2 on purpose and now says why in `build.mill`: it
+  must match the Scala that Mill 1.1.x compiles build files with, or consumers hit a TASTy version
+  error at build-script compile time.
+- Managed Bun default **1.4.0 → 1.4.1** (released 2026-09-04), with checksums for all twelve
+  release assets; 1.4.1 writes `lockfileVersion` 2, so committed locks stay valid. 1.4.0 stays in
+  the table for explicit `bunVersion` pins. `@types/bun` has not reached 1.4.1 on npm yet, so the
+  shipped default pairs with `DefaultBunTypesVersion = "1.4.0"` rather than tracking Bun blindly
+  (a 404 on every TypeScript frozen install); modules that override `bunVersion` keep lockstep.
+
 ## [0.3.0] - Managed toolchain, strict lockfiles, canonical vocabulary (2026-08-27)
 
 ### Added
diff --git a/README.md b/README.md
index aaa881f..b104b7e 100644
--- a/README.md
+++ b/README.md
@@ -6,18 +6,18 @@ It keeps Mill's task graph, caching, module relationships, Scala.js linker, and
 
 ## Requirements
 
-- Mill 1.1.5+
+- Mill 1.1.5+ (compiled against 1.1.5; the test suite and examples run on 1.1.8)
 - JDK 17+
 
-Bun does not need to be installed. The plugin downloads and checksum-verifies Bun 1.4.0 by default on macOS, Linux, and Windows x64/arm64. musl-based Linux (Alpine) is detected automatically; on x64 CPUs without AVX2, set `bunUseBaseline`. Set `MILL_BUN_USE_SYSTEM=true` to opt into the Bun on `PATH` instead.
+Bun does not need to be installed. The plugin downloads and checksum-verifies Bun 1.4.1 by default on macOS, Linux, and Windows x64/arm64. musl-based Linux (Alpine) is detected automatically; on x64 CPUs without AVX2, set `bunUseBaseline`. Set `MILL_BUN_USE_SYSTEM=true` to opt into the Bun on `PATH` instead.
 
 ## Scala.js quick start
 
 ```scala
-//| mill-version: 1.1.5
+//| mill-version: 1.1.8
 //| mill-jvm-version: system
 //| mvnDeps:
-//| - com.tjclp::mill-bun_mill1:0.3.0
+//| - com.tjclp::mill-bun_mill1:0.3.1
 
 package build
 
@@ -29,7 +29,7 @@ import mill.scalajslib.bun.*
 
 object app extends BunScalaJSModule {
   override def moduleDir = build.moduleDir
-  def scalaVersion = "3.8.2"
+  def scalaVersion = "3.9.0"
   def scalaJSVersion = "1.22.0"
 
   override def moduleKind = Task { ModuleKind.ESModule }
@@ -57,10 +57,10 @@ Scala.js versions are explicit: choose the version your application tests agains
 ## TypeScript quick start
 
 ```scala
-//| mill-version: 1.1.5
+//| mill-version: 1.1.8
 //| mill-jvm-version: system
 //| mvnDeps:
-//| - com.tjclp::mill-bun_mill1:0.3.0
+//| - com.tjclp::mill-bun_mill1:0.3.1
 
 package build
 
@@ -89,7 +89,7 @@ Use the paired web traits when HTML and static assets are part of the applicatio
 
 ```scala
 object frontend extends BunScalaJSWebModule {
-  def scalaVersion = "3.8.2"
+  def scalaVersion = "3.9.0"
   def scalaJSVersion = "1.22.0"
   override def moduleKind = Task { ModuleKind.ESModule }
 }
@@ -133,7 +133,7 @@ Resolution order is:
 
 1. `bunExecutableOverride`
 2. system `PATH` when `bunUseSystem` or `MILL_BUN_USE_SYSTEM=true`
-3. checksum-verified managed Bun 1.4.0
+3. checksum-verified managed Bun 1.4.1
 
 Use `./mill app.bunDoctor` to print and validate the resolved executable, version, revision, mode, selected release asset, and linker.
 
@@ -156,7 +156,7 @@ import mill.javascriptlib.bun.*
 import mill.scalajslib.bun.*
 
 object scalaApp extends BunScalaJSModule {
-  def scalaVersion = "3.8.2"
+  def scalaVersion = "3.9.0"
   def scalaJSVersion = "1.22.0"
   override def bunWorkspaceInstall = Task { Some(workspace.bunInstall()) }
 }
@@ -178,7 +178,7 @@ Mix `BunPublishModule` into a published Scala.js library to emit `META-INF/bun/b
 
 ```scala
 object ui extends BunScalaJSModule with BunPublishModule {
-  def scalaVersion = "3.8.2"
+  def scalaVersion = "3.9.0"
   def scalaJSVersion = "1.22.0"
   override def npmPeerDeps = Task { Seq("react@^19.0.0") }
 }
diff --git a/build.mill b/build.mill
index 39c8df5..9d4a979 100644
--- a/build.mill
+++ b/build.mill
@@ -4,7 +4,18 @@ import mill.*, scalalib.*, publish.*
 import mill.api.BuildCtx
 
 object millbun extends ScalaModule, PublishModule {
+  // Compile target = the minimum Mill the plugin supports; Mill 1.x keeps plugin binary
+  // compatibility forwards, so the floor stays where it is while the suite below runs on
+  // the latest stable release.
   def millVersion = "1.1.5"
+  // The integration fixtures run Mill in-process via mill-testkit, so THIS is the Mill the
+  // plugin is tested against (fixture `//| mill-version` headers are only read for the
+  // mismatch warning). Kept at the latest stable Mill; the plugin jar under test is still
+  // the one compiled against millVersion above, i.e. the real consumer shape.
+  def millTestkitVersion = "1.1.8"
+  // Must match the Scala that Mill 1.1.x compiles build files with (3.8.2): a plugin built
+  // with a newer Scala emits TASTy that consumers' Mill cannot read. Fixtures and examples
+  // are free to use newer Scala (they are on 3.9.0 LTS); this pin is not.
   def scalaVersion = "3.8.2"
   def jvmVersion = "25"
   def platformSuffix = "_mill1"
@@ -24,7 +35,7 @@ object millbun extends ScalaModule, PublishModule {
 
   object integration extends ScalaTests, TestModule.Utest {
     def mvnDeps = Seq(
-      mvn"com.lihaoyi::mill-testkit:$millVersion",
+      mvn"com.lihaoyi::mill-testkit:$millTestkitVersion",
       mvn"com.lihaoyi::utest:0.8.5"
     )
     override def resources = Task.Sources()
diff --git a/example-scalajs/build.mill b/example-scalajs/build.mill
index bffdc70..c0fa88c 100644
--- a/example-scalajs/build.mill
+++ b/example-scalajs/build.mill
@@ -1,7 +1,7 @@
-//| mill-version: 1.1.5
+//| mill-version: 1.1.8
 //| mill-jvm-version: system
 //| mvnDeps:
-//| - com.tjclp::mill-bun_mill1:0.3.0
+//| - com.tjclp::mill-bun_mill1:0.3.1
 
 package build
 
@@ -14,7 +14,7 @@ import mill.bun.bun
 
 object app extends BunScalaJSModule {
   override def moduleDir = build.moduleDir
-  def scalaVersion = "3.8.2"
+  def scalaVersion = "3.9.0"
   def scalaJSVersion = "1.22.0"
 
   override def moduleKind = Task { ModuleKind.ESModule }
diff --git a/example-scalajs/mill b/example-scalajs/mill
index 155baa7..29f7b4f 100755
--- a/example-scalajs/mill
+++ b/example-scalajs/mill
@@ -2,7 +2,7 @@
 
 set -e
 
-if [ -z "${DEFAULT_MILL_VERSION}" ] ; then DEFAULT_MILL_VERSION="1.1.5"; fi
+if [ -z "${DEFAULT_MILL_VERSION}" ] ; then DEFAULT_MILL_VERSION="1.1.8"; fi
 
 if [ -z "${GITHUB_RELEASE_CDN}" ] ; then GITHUB_RELEASE_CDN=""; fi
 
diff --git a/example-scalajs/mill.bat b/example-scalajs/mill.bat
index 948392f..1bce54c 100644
--- a/example-scalajs/mill.bat
+++ b/example-scalajs/mill.bat
@@ -2,7 +2,7 @@
 
 setlocal enabledelayedexpansion
 
-if [!DEFAULT_MILL_VERSION!]==[] ( set "DEFAULT_MILL_VERSION=1.1.5" )
+if [!DEFAULT_MILL_VERSION!]==[] ( set "DEFAULT_MILL_VERSION=1.1.8" )
 
 if [!MILL_GITHUB_RELEASE_CDN!]==[] ( set "MILL_GITHUB_RELEASE_CDN=" )
 
diff --git a/example-typescript/build.mill b/example-typescript/build.mill
index 72904ae..58de38e 100644
--- a/example-typescript/build.mill
+++ b/example-typescript/build.mill
@@ -1,7 +1,7 @@
-//| mill-version: 1.1.5
+//| mill-version: 1.1.8
 //| mill-jvm-version: system
 //| mvnDeps:
-//| - com.tjclp::mill-bun_mill1:0.3.0
+//| - com.tjclp::mill-bun_mill1:0.3.1
 
 package build
 
diff --git a/example-typescript/mill b/example-typescript/mill
index 155baa7..29f7b4f 100755
--- a/example-typescript/mill
+++ b/example-typescript/mill
@@ -2,7 +2,7 @@
 
 set -e
 
-if [ -z "${DEFAULT_MILL_VERSION}" ] ; then DEFAULT_MILL_VERSION="1.1.5"; fi
+if [ -z "${DEFAULT_MILL_VERSION}" ] ; then DEFAULT_MILL_VERSION="1.1.8"; fi
 
 if [ -z "${GITHUB_RELEASE_CDN}" ] ; then GITHUB_RELEASE_CDN=""; fi
 
diff --git a/example-typescript/mill.bat b/example-typescript/mill.bat
index 948392f..1bce54c 100644
--- a/example-typescript/mill.bat
+++ b/example-typescript/mill.bat
@@ -2,7 +2,7 @@
 
 setlocal enabledelayedexpansion
 
-if [!DEFAULT_MILL_VERSION!]==[] ( set "DEFAULT_MILL_VERSION=1.1.5" )
+if [!DEFAULT_MILL_VERSION!]==[] ( set "DEFAULT_MILL_VERSION=1.1.8" )
 
 if [!MILL_GITHUB_RELEASE_CDN!]==[] ( set "MILL_GITHUB_RELEASE_CDN=" )
 
diff --git a/examples/build.mill b/examples/build.mill
index 12e20a9..654bbc8 100644
--- a/examples/build.mill
+++ b/examples/build.mill
@@ -1,7 +1,7 @@
-//| mill-version: 1.1.5
+//| mill-version: 1.1.8
 //| mill-jvm-version: system
 //| mvnDeps:
-//| - com.tjclp::mill-bun_mill1:0.3.0
+//| - com.tjclp::mill-bun_mill1:0.3.1
 
 package build
 
@@ -22,7 +22,7 @@ import mill.javascriptlib.bun.*
 // ./mill webServer.compileExecutable
 object webServer extends BunScalaJSModule {
   override def sources = Task.Sources(build.moduleDir / "web-server" / "src")
-  def scalaVersion = "3.8.2"
+  def scalaVersion = "3.9.0"
   def scalaJSVersion = "1.22.0"
   override def moduleKind = Task { ModuleKind.ESModule }
   override def bunBundleTarget = Task { "bun" }
@@ -32,7 +32,7 @@ object webServer extends BunScalaJSModule {
 // ./mill todoApp.bundle
 object todoApp extends BunScalaJSModule {
   override def sources = Task.Sources(build.moduleDir / "frontend" / "src")
-  def scalaVersion = "3.8.2"
+  def scalaVersion = "3.9.0"
   def scalaJSVersion = "1.22.0"
   def mvnDeps = Seq(mvn"org.scala-js::scalajs-dom::2.8.1")
   override def moduleKind = Task { ModuleKind.ESModule }
@@ -46,7 +46,7 @@ object todoApp extends BunScalaJSModule {
 object fullstack extends Module {
   object shared extends BunScalaJSModule {
     override def sources = Task.Sources(build.moduleDir / "fullstack" / "shared")
-    def scalaVersion = "3.8.2"
+    def scalaVersion = "3.9.0"
     def scalaJSVersion = "1.22.0"
     override def moduleKind = Task { ModuleKind.ESModule }
   }
@@ -107,7 +107,7 @@ object client extends BunTypeScriptModule {
 
 // --- Scala.js browser frontend (alternative client) ---
 object scalaClient extends BunScalaJSModule {
-  def scalaVersion = "3.8.2"
+  def scalaVersion = "3.9.0"
   def scalaJSVersion = "1.22.0"
   def mvnDeps = Seq(mvn"org.scala-js::scalajs-dom::2.8.1")
   override def moduleKind = Task { ModuleKind.ESModule }
@@ -116,7 +116,7 @@ object scalaClient extends BunScalaJSModule {
 
 // --- JVM backend (Scala/Cask HTTP server, serves TS client bundle) ---
 object backend extends ScalaModule {
-  def scalaVersion = "3.8.2"
+  def scalaVersion = "3.9.0"
   def mvnDeps = Seq(
     mvn"com.lihaoyi::cask:0.10.2",
     mvn"com.lihaoyi::upickle:4.3.0"
diff --git a/mill b/mill
index 155baa7..29f7b4f 100755
--- a/mill
+++ b/mill
@@ -2,7 +2,7 @@
 
 set -e
 
-if [ -z "${DEFAULT_MILL_VERSION}" ] ; then DEFAULT_MILL_VERSION="1.1.5"; fi
+if [ -z "${DEFAULT_MILL_VERSION}" ] ; then DEFAULT_MILL_VERSION="1.1.8"; fi
 
 if [ -z "${GITHUB_RELEASE_CDN}" ] ; then GITHUB_RELEASE_CDN=""; fi
 
diff --git a/mill.bat b/mill.bat
index 948392f..1bce54c 100644
--- a/mill.bat
+++ b/mill.bat
@@ -2,7 +2,7 @@
 
 setlocal enabledelayedexpansion
 
-if [!DEFAULT_MILL_VERSION!]==[] ( set "DEFAULT_MILL_VERSION=1.1.5" )
+if [!DEFAULT_MILL_VERSION!]==[] ( set "DEFAULT_MILL_VERSION=1.1.8" )
 
 if [!MILL_GITHUB_RELEASE_CDN!]==[] ( set "MILL_GITHUB_RELEASE_CDN=" )
 
diff --git a/millbun/integration/resources/invalid-bun-literal/build.mill b/millbun/integration/resources/invalid-bun-literal/build.mill
index 548ca07..0918017 100644
--- a/millbun/integration/resources/invalid-bun-literal/build.mill
+++ b/millbun/integration/resources/invalid-bun-literal/build.mill
@@ -1,4 +1,4 @@
-//| mill-version: 1.1.5
+//| mill-version: 1.1.8
 //| mill-jvm-version: system
 //| mvnDeps:
 //| - com.tjclp::mill-bun_mill1:0.0.0-NIGHTLY
@@ -13,7 +13,7 @@ import mill.scalajslib.bun.*
 
 object app extends BunScalaJSModule {
   override def moduleDir = build.moduleDir
-  def scalaVersion = "3.8.2"
+  def scalaVersion = "3.9.0"
   def scalaJSVersion = "1.22.0"
 
   override def moduleKind = Task { ModuleKind.CommonJSModule }
diff --git a/millbun/integration/resources/invalid-bun-specifier/build.mill b/millbun/integration/resources/invalid-bun-specifier/build.mill
index 3699c20..c2894d9 100644
--- a/millbun/integration/resources/invalid-bun-specifier/build.mill
+++ b/millbun/integration/resources/invalid-bun-specifier/build.mill
@@ -1,4 +1,4 @@
-//| mill-version: 1.1.5
+//| mill-version: 1.1.8
 //| mill-jvm-version: system
 //| mvnDeps:
 //| - com.tjclp::mill-bun_mill1:0.0.0-NIGHTLY
@@ -13,7 +13,7 @@ import mill.scalajslib.bun.*
 
 object app extends BunScalaJSModule {
   override def moduleDir = build.moduleDir
-  def scalaVersion = "3.8.2"
+  def scalaVersion = "3.9.0"
   def scalaJSVersion = "1.22.0"
 
   override def moduleKind = Task { ModuleKind.CommonJSModule }
diff --git a/millbun/integration/resources/managed-bun/build.mill b/millbun/integration/resources/managed-bun/build.mill
index 3fa5678..6aeaf11 100644
--- a/millbun/integration/resources/managed-bun/build.mill
+++ b/millbun/integration/resources/managed-bun/build.mill
@@ -1,4 +1,4 @@
-//| mill-version: 1.1.5
+//| mill-version: 1.1.8
 //| mill-jvm-version: system
 //| mvnDeps:
 //| - com.tjclp::mill-bun_mill1:0.0.0-NIGHTLY
diff --git a/millbun/integration/resources/mixed-workspace/build.mill b/millbun/integration/resources/mixed-workspace/build.mill
index d85e2e4..5001075 100644
--- a/millbun/integration/resources/mixed-workspace/build.mill
+++ b/millbun/integration/resources/mixed-workspace/build.mill
@@ -1,4 +1,4 @@
-//| mill-version: 1.1.5
+//| mill-version: 1.1.8
 //| mill-jvm-version: system
 //| mvnDeps:
 //| - com.tjclp::mill-bun_mill1:0.0.0-NIGHTLY
@@ -15,7 +15,7 @@ object scalaApp extends BunScalaJSModule {
   // Renamed deliberately: the layout's directory naming, duplicate guard, AND the generated
   // member manifest must all follow this name, or bun sees a different identity than Mill.
   override def bunWorkspacePackageName = Task { "scala-app-renamed" }
-  def scalaVersion = "3.8.2"
+  def scalaVersion = "3.9.0"
   def scalaJSVersion = "1.22.0"
   override def moduleKind = Task { ModuleKind.ESModule }
   override def npmDeps = Task { Seq("is-even@1.0.0") }
diff --git a/millbun/integration/resources/scalajs-bundle/build.mill b/millbun/integration/resources/scalajs-bundle/build.mill
index 7112db3..7cd9882 100644
--- a/millbun/integration/resources/scalajs-bundle/build.mill
+++ b/millbun/integration/resources/scalajs-bundle/build.mill
@@ -1,4 +1,4 @@
-//| mill-version: 1.1.5
+//| mill-version: 1.1.8
 //| mill-jvm-version: system
 //| mvnDeps:
 //| - com.tjclp::mill-bun_mill1:0.0.0-NIGHTLY
@@ -12,7 +12,7 @@ import mill.scalajslib.bun.*
 
 object app extends BunScalaJSModule {
   override def moduleDir = build.moduleDir
-  def scalaVersion = "3.8.2"
+  def scalaVersion = "3.9.0"
   def scalaJSVersion = "1.22.0"
 
   override def mainClass = Some("Main")
diff --git a/millbun/integration/resources/scalajs-bunfig/build.mill b/millbun/integration/resources/scalajs-bunfig/build.mill
index bbe37e9..8b55dc4 100644
--- a/millbun/integration/resources/scalajs-bunfig/build.mill
+++ b/millbun/integration/resources/scalajs-bunfig/build.mill
@@ -1,4 +1,4 @@
-//| mill-version: 1.1.5
+//| mill-version: 1.1.8
 //| mill-jvm-version: system
 //| mvnDeps:
 //| - com.tjclp::mill-bun_mill1:0.0.0-NIGHTLY
@@ -13,7 +13,7 @@ import mill.scalajslib.bun.*
 
 object app extends BunScalaJSModule {
   override def moduleDir = build.moduleDir
-  def scalaVersion = "3.8.2"
+  def scalaVersion = "3.9.0"
   def scalaJSVersion = "1.22.0"
 
   override def mainClass = Some("Main")
diff --git a/millbun/integration/resources/scalajs-dependency-manifests/build.mill b/millbun/integration/resources/scalajs-dependency-manifests/build.mill
index 1646f15..5be83d3 100644
--- a/millbun/integration/resources/scalajs-dependency-manifests/build.mill
+++ b/millbun/integration/resources/scalajs-dependency-manifests/build.mill
@@ -1,4 +1,4 @@
-//| mill-version: 1.1.5
+//| mill-version: 1.1.8
 //| mill-jvm-version: system
 //| mvnDeps:
 //| - com.tjclp::mill-bun_mill1:0.0.0-NIGHTLY
@@ -13,7 +13,7 @@ import mill.scalajslib.bun.*
 
 trait StubBunModule extends BunScalaJSModule {
   override def moduleDir = build.moduleDir
-  def scalaVersion = "3.8.2"
+  def scalaVersion = "3.9.0"
   def scalaJSVersion = "1.22.0"
   override def moduleKind = Task { ModuleKind.CommonJSModule }
   override def bunExecutable = Task { "stub-bun" }
diff --git a/millbun/integration/resources/scalajs-simple/build.mill b/millbun/integration/resources/scalajs-simple/build.mill
index f1d2d36..175ba89 100644
--- a/millbun/integration/resources/scalajs-simple/build.mill
+++ b/millbun/integration/resources/scalajs-simple/build.mill
@@ -1,4 +1,4 @@
-//| mill-version: 1.1.5
+//| mill-version: 1.1.8
 //| mill-jvm-version: system
 //| mvnDeps:
 //| - com.tjclp::mill-bun_mill1:0.0.0-NIGHTLY
@@ -12,7 +12,7 @@ import mill.scalajslib.bun.*
 
 object app extends BunScalaJSModule {
   override def moduleDir = build.moduleDir
-  def scalaVersion = "3.8.2"
+  def scalaVersion = "3.9.0"
   def scalaJSVersion = "1.22.0"
 
   override def moduleKind = Task { ModuleKind.ESModule }
diff --git a/millbun/integration/resources/scalajs-test/build.mill b/millbun/integration/resources/scalajs-test/build.mill
index 0e9b278..07a88b4 100644
--- a/millbun/integration/resources/scalajs-test/build.mill
+++ b/millbun/integration/resources/scalajs-test/build.mill
@@ -1,4 +1,4 @@
-//| mill-version: 1.1.5
+//| mill-version: 1.1.8
 //| mill-jvm-version: system
 //| mvnDeps:
 //| - com.tjclp::mill-bun_mill1:0.0.0-NIGHTLY
@@ -13,7 +13,7 @@ import mill.scalajslib.bun.*
 
 object app extends BunScalaJSModule {
   override def moduleDir = build.moduleDir
-  def scalaVersion = "3.8.2"
+  def scalaVersion = "3.9.0"
   def scalaJSVersion = "1.22.0"
 
   override def moduleKind = Task { ModuleKind.ESModule }
diff --git a/millbun/integration/resources/scalajs-transitive/build.mill b/millbun/integration/resources/scalajs-transitive/build.mill
index 1cbbf76..f537c40 100644
--- a/millbun/integration/resources/scalajs-transitive/build.mill
+++ b/millbun/integration/resources/scalajs-transitive/build.mill
@@ -1,4 +1,4 @@
-//| mill-version: 1.1.5
+//| mill-version: 1.1.8
 //| mill-jvm-version: system
 //| mvnDeps:
 //| - com.tjclp::mill-bun_mill1:0.0.0-NIGHTLY
@@ -13,7 +13,7 @@ import mill.scalajslib.bun.*
 // lib keeps its own moduleDir (lib/): sharing the root with app would make both modules
 // resolve the same bun.lock, and only one dependency set can be recorded there.
 object lib extends BunScalaJSModule {
-  def scalaVersion = "3.8.2"
+  def scalaVersion = "3.9.0"
   def scalaJSVersion = "1.22.0"
 
   override def moduleKind = Task { ModuleKind.ESModule }
diff --git a/millbun/integration/resources/scalajs-web/build.mill b/millbun/integration/resources/scalajs-web/build.mill
index 853e71b..cdc8af8 100644
--- a/millbun/integration/resources/scalajs-web/build.mill
+++ b/millbun/integration/resources/scalajs-web/build.mill
@@ -1,4 +1,4 @@
-//| mill-version: 1.1.5
+//| mill-version: 1.1.8
 //| mill-jvm-version: system
 //| mvnDeps:
 //| - com.tjclp::mill-bun_mill1:0.0.0-NIGHTLY
@@ -13,7 +13,7 @@ import mill.scalajslib.bun.*
 
 object app extends BunScalaJSWebModule {
   override def moduleDir = build.moduleDir
-  def scalaVersion = "3.8.2"
+  def scalaVersion = "3.9.0"
   def scalaJSVersion = "1.22.0"
   def mvnDeps = Seq(mvn"org.scala-js::scalajs-dom::2.8.1")
   override def npmDeps = Task { Seq("lodash@4.17.21") }
diff --git a/millbun/integration/resources/typescript-browser/build.mill b/millbun/integration/resources/typescript-browser/build.mill
index b14146b..dd77c57 100644
--- a/millbun/integration/resources/typescript-browser/build.mill
+++ b/millbun/integration/resources/typescript-browser/build.mill
@@ -1,4 +1,4 @@
-//| mill-version: 1.1.5
+//| mill-version: 1.1.8
 //| mill-jvm-version: system
 //| mvnDeps:
 //| - com.tjclp::mill-bun_mill1:0.0.0-NIGHTLY
diff --git a/millbun/integration/resources/typescript-bundle/build.mill b/millbun/integration/resources/typescript-bundle/build.mill
index 3b296da..dc10d49 100644
--- a/millbun/integration/resources/typescript-bundle/build.mill
+++ b/millbun/integration/resources/typescript-bundle/build.mill
@@ -1,4 +1,4 @@
-//| mill-version: 1.1.5
+//| mill-version: 1.1.8
 //| mill-jvm-version: system
 //| mvnDeps:
 //| - com.tjclp::mill-bun_mill1:0.0.0-NIGHTLY
diff --git a/millbun/integration/resources/typescript-bunfig/build.mill b/millbun/integration/resources/typescript-bunfig/build.mill
index 3edc3c7..d9e63be 100644
--- a/millbun/integration/resources/typescript-bunfig/build.mill
+++ b/millbun/integration/resources/typescript-bunfig/build.mill
@@ -1,4 +1,4 @@
-//| mill-version: 1.1.5
+//| mill-version: 1.1.8
 //| mill-jvm-version: system
 //| mvnDeps:
 //| - com.tjclp::mill-bun_mill1:0.0.0-NIGHTLY
diff --git a/millbun/integration/resources/typescript-compile/build.mill b/millbun/integration/resources/typescript-compile/build.mill
index 2dbf47d..848ddc7 100644
--- a/millbun/integration/resources/typescript-compile/build.mill
+++ b/millbun/integration/resources/typescript-compile/build.mill
@@ -1,4 +1,4 @@
-//| mill-version: 1.1.5
+//| mill-version: 1.1.8
 //| mill-jvm-version: system
 //| mvnDeps:
 //| - com.tjclp::mill-bun_mill1:0.0.0-NIGHTLY
diff --git a/millbun/integration/resources/typescript-env/build.mill b/millbun/integration/resources/typescript-env/build.mill
index 686ac00..32151ab 100644
--- a/millbun/integration/resources/typescript-env/build.mill
+++ b/millbun/integration/resources/typescript-env/build.mill
@@ -1,4 +1,4 @@
-//| mill-version: 1.1.5
+//| mill-version: 1.1.8
 //| mill-jvm-version: system
 //| mvnDeps:
 //| - com.tjclp::mill-bun_mill1:0.0.0-NIGHTLY
diff --git a/millbun/integration/resources/typescript-lock/build.mill b/millbun/integration/resources/typescript-lock/build.mill
index c39c529..d138600 100644
--- a/millbun/integration/resources/typescript-lock/build.mill
+++ b/millbun/integration/resources/typescript-lock/build.mill
@@ -1,4 +1,4 @@
-//| mill-version: 1.1.5
+//| mill-version: 1.1.8
 //| mill-jvm-version: system
 //| mvnDeps:
 //| - com.tjclp::mill-bun_mill1:0.0.0-NIGHTLY
diff --git a/millbun/integration/resources/typescript-overrides/build.mill b/millbun/integration/resources/typescript-overrides/build.mill
index f6c07ee..6bd1d75 100644
--- a/millbun/integration/resources/typescript-overrides/build.mill
+++ b/millbun/integration/resources/typescript-overrides/build.mill
@@ -1,4 +1,4 @@
-//| mill-version: 1.1.5
+//| mill-version: 1.1.8
 //| mill-jvm-version: system
 //| mvnDeps:
 //| - com.tjclp::mill-bun_mill1:0.0.0-NIGHTLY
diff --git a/millbun/integration/resources/typescript-simple/build.mill b/millbun/integration/resources/typescript-simple/build.mill
index e714a76..44f1e4c 100644
--- a/millbun/integration/resources/typescript-simple/build.mill
+++ b/millbun/integration/resources/typescript-simple/build.mill
@@ -1,4 +1,4 @@
-//| mill-version: 1.1.5
+//| mill-version: 1.1.8
 //| mill-jvm-version: system
 //| mvnDeps:
 //| - com.tjclp::mill-bun_mill1:0.0.0-NIGHTLY
diff --git a/millbun/integration/resources/typescript-stale-lock/build.mill b/millbun/integration/resources/typescript-stale-lock/build.mill
index b60587c..244f207 100644
--- a/millbun/integration/resources/typescript-stale-lock/build.mill
+++ b/millbun/integration/resources/typescript-stale-lock/build.mill
@@ -1,4 +1,4 @@
-//| mill-version: 1.1.5
+//| mill-version: 1.1.8
 //| mill-jvm-version: system
 //| mvnDeps:
 //| - com.tjclp::mill-bun_mill1:0.0.0-NIGHTLY
diff --git a/millbun/integration/resources/typescript-test-deps/build.mill b/millbun/integration/resources/typescript-test-deps/build.mill
index a315dd8..a11471a 100644
--- a/millbun/integration/resources/typescript-test-deps/build.mill
+++ b/millbun/integration/resources/typescript-test-deps/build.mill
@@ -1,4 +1,4 @@
-//| mill-version: 1.1.5
+//| mill-version: 1.1.8
 //| mill-jvm-version: system
 //| mvnDeps:
 //| - com.tjclp::mill-bun_mill1:0.0.0-NIGHTLY
diff --git a/millbun/integration/resources/typescript-tests/build.mill b/millbun/integration/resources/typescript-tests/build.mill
index 3e3731f..448779f 100644
--- a/millbun/integration/resources/typescript-tests/build.mill
+++ b/millbun/integration/resources/typescript-tests/build.mill
@@ -1,4 +1,4 @@
-//| mill-version: 1.1.5
+//| mill-version: 1.1.8
 //| mill-jvm-version: system
 //| mvnDeps:
 //| - com.tjclp::mill-bun_mill1:0.0.0-NIGHTLY
diff --git a/millbun/integration/resources/typescript-tsx/build.mill b/millbun/integration/resources/typescript-tsx/build.mill
index c9710be..08e9b8d 100644
--- a/millbun/integration/resources/typescript-tsx/build.mill
+++ b/millbun/integration/resources/typescript-tsx/build.mill
@@ -1,4 +1,4 @@
-//| mill-version: 1.1.5
+//| mill-version: 1.1.8
 //| mill-jvm-version: system
 //| mvnDeps:
 //| - com.tjclp::mill-bun_mill1:0.0.0-NIGHTLY
diff --git a/millbun/integration/resources/typescript-unmanaged/build.mill b/millbun/integration/resources/typescript-unmanaged/build.mill
index 1333f47..1a7fca5 100644
--- a/millbun/integration/resources/typescript-unmanaged/build.mill
+++ b/millbun/integration/resources/typescript-unmanaged/build.mill
@@ -1,4 +1,4 @@
-//| mill-version: 1.1.5
+//| mill-version: 1.1.8
 //| mill-jvm-version: system
 //| mvnDeps:
 //| - com.tjclp::mill-bun_mill1:0.0.0-NIGHTLY
diff --git a/millbun/integration/resources/typescript-web/build.mill b/millbun/integration/resources/typescript-web/build.mill
index ac9bebd..0def87c 100644
--- a/millbun/integration/resources/typescript-web/build.mill
+++ b/millbun/integration/resources/typescript-web/build.mill
@@ -1,4 +1,4 @@
-//| mill-version: 1.1.5
+//| mill-version: 1.1.8
 //| mill-jvm-version: system
 //| mvnDeps:
 //| - com.tjclp::mill-bun_mill1:0.0.0-NIGHTLY
diff --git a/millbun/integration/resources/typescript-workers/build.mill b/millbun/integration/resources/typescript-workers/build.mill
index 50724d0..33c8fbb 100644
--- a/millbun/integration/resources/typescript-workers/build.mill
+++ b/millbun/integration/resources/typescript-workers/build.mill
@@ -1,4 +1,4 @@
-//| mill-version: 1.1.5
+//| mill-version: 1.1.8
 //| mill-jvm-version: system
 //| mvnDeps:
 //| - com.tjclp::mill-bun_mill1:0.0.0-NIGHTLY
diff --git a/millbun/integration/src/mill/bun/BunManagedToolchainIntegrationTests.scala b/millbun/integration/src/mill/bun/BunManagedToolchainIntegrationTests.scala
index 4d5a4a2..4ddc0d1 100644
--- a/millbun/integration/src/mill/bun/BunManagedToolchainIntegrationTests.scala
+++ b/millbun/integration/src/mill/bun/BunManagedToolchainIntegrationTests.scala
@@ -12,7 +12,7 @@ object BunManagedToolchainIntegrationTests extends BunIntegrationSuite:
       assert(result.isSuccess)
       val executable = tester.out("app.bunExecutable").value[String]
       val version = os.proc(executable, "--version").call(stdout = os.Pipe).out.text().trim
-      assert(version == "1.4.0")
+      assert(version == BunToolchainModule.DefaultBunVersion)
       // First-ever coverage for the diagnostics command: it must at least evaluate.
       assert(tester.eval("app.bunDoctor").isSuccess)
 
@@ -40,4 +40,4 @@ object BunManagedToolchainIntegrationTests extends BunIntegrationSuite:
       val executable = tester.out("app.bunExecutable").value[String]
       assert(os.isFile(os.Path(executable)))
       val version = os.proc(executable, "--version").call(stdout = os.Pipe).out.text().trim
-      assert(version == "1.4.0")
+      assert(version == BunToolchainModule.DefaultBunVersion)
diff --git a/millbun/integration/src/mill/bun/BunTypeScriptIntegrationTests.scala b/millbun/integration/src/mill/bun/BunTypeScriptIntegrationTests.scala
index 7407015..350583f 100644
--- a/millbun/integration/src/mill/bun/BunTypeScriptIntegrationTests.scala
+++ b/millbun/integration/src/mill/bun/BunTypeScriptIntegrationTests.scala
@@ -135,8 +135,9 @@ object BunTypeScriptIntegrationTests extends BunIntegrationSuite {
       val packageJson = ujson.read(os.read(tester.workspacePath / "out" / "app" / "bunInstall.dest" / "package.json"))
       val devDeps = packageJson("devDependencies").obj
 
-      // Pinned, and pinned to the Bun we ship: @types/bun is published in lockstep with Bun.
-      assert(devDeps("@types/bun").str == BunToolchainModule.DefaultBunVersion)
+      // Pinned, and pinned to the types that pair with the Bun we ship. That is normally the same
+      // number, but npm can lag a Bun release, so the default carries its own types version.
+      assert(devDeps("@types/bun").str == BunToolchainModule.DefaultBunTypesVersion)
       assert(devDeps("@types/bun").str != "latest")
       assert(!devDeps.contains("@types/node"))
     }
diff --git a/millbun/src/mill/bun/BunToolchainModule.scala b/millbun/src/mill/bun/BunToolchainModule.scala
index b9f68e0..692b146 100644
--- a/millbun/src/mill/bun/BunToolchainModule.scala
+++ b/millbun/src/mill/bun/BunToolchainModule.scala
@@ -13,10 +13,21 @@ object BunToolchainModule {
   /**
    * The Bun release this plugin is tested against and downloads by default.
    *
-   * Referenced by `bunVersion`, by `bunTypesVersion` (`@types/bun` is published in lockstep), and
-   * by the tests, so a bump is a one-line change here rather than a hunt for literals.
+   * Referenced by `bunVersion` and by the tests, so a bump is a one-line change here (plus the
+   * checksum row below) rather than a hunt for literals.
    */
-  val DefaultBunVersion = "1.4.0"
+  val DefaultBunVersion = "1.4.1"
+
+  /**
+   * `@types/bun` version paired with [[DefaultBunVersion]] by default.
+   *
+   * `@types/bun` normally ships in lockstep with Bun, but npm can lag a release by a day or two
+   * (1.4.1 shipped 2026-09-04 with no `@types/bun@1.4.1` yet). Tracking Bun blindly would make
+   * every TypeScript module's frozen install 404 on release day, so the shipped default pins the
+   * newest published types instead. Bump together with [[DefaultBunVersion]] once npm has caught
+   * up; modules that override `bunVersion` keep the lockstep behaviour.
+   */
+  val DefaultBunTypesVersion = "1.4.0"
 
   private val ModeledPackageJsonFields = Set(
     "dependencies",
@@ -69,16 +80,31 @@ object BunToolchainModule {
       "bun-windows-aarch64.zip" -> "f473bfe2df73ee770548c93dd5d380aea7120c218ec2aa1afdd0bbba7bf18c47",
       "bun-windows-x64.zip" -> "e6f093d39da486b20262ca8cdd5ed6a9e8bc9c2f275b78e6d3a0c5b28cc95901",
       "bun-windows-x64-baseline.zip" -> "b929c54a9badb104a16dedd23aab6152c86793ae653d4e6b13983ffd0c882a66"
+    ),
+    "1.4.1" -> Map(
+      "bun-darwin-aarch64.zip" -> "d8973ce835fa7867e5cc79afee6fc6f1ae0117aa4bd5fc2546fd00c512f71386",
+      "bun-darwin-x64.zip" -> "8f34239f276a3f0d27bfcd1ffecfe5d2127e74fb0aa4c0971a0cdec7b225c965",
+      "bun-darwin-x64-baseline.zip" -> "498e76d61bbe87d2306f65fed60ae86b6b0c8ee2da709f83202808db1a09e407",
+      "bun-linux-aarch64.zip" -> "580ce77533108dc6b10bec1721397e4f5aa44e909726da2451d483dfc5e581d6",
+      "bun-linux-aarch64-musl.zip" -> "53895807a00508f70e76715947097aa533ec520aac066501c00fb77d2b1a7a6c",
+      "bun-linux-x64.zip" -> "74c1c3bee7cd998500c8f969cd8972355ac6a07207e94a39eece1999b56ffabf",
+      "bun-linux-x64-baseline.zip" -> "a8c9c6738202e2fced555dd860a953c56c0cd059f75041e7010ae81a32802646",
+      "bun-linux-x64-musl.zip" -> "ea116fe09f2f764c87b9bf735225b781d1f7674ca58d66040470f38a7943c8ab",
+      "bun-linux-x64-musl-baseline.zip" -> "74d04038a21e6ae816f9e74525b754b85294be99632b336cb4c57019c9313829",
+      "bun-windows-aarch64.zip" -> "41ea66155baf0ac1f8545f8d54544bcaf4908104193c5db9aad85d6f53ae1bd7",
+      "bun-windows-x64.zip" -> "52b1f3028b01f43d37fefdf669d034a1ee2e0d96c56bb13c393bdaf169b1af84",
+      "bun-windows-x64-baseline.zip" -> "2d1871e72b28165a8574a9c91de867cbe499f55b8c75facf4fb9e42888eddba6"
     )
   )
 
   /** Versions with a complete bundled checksum table, for diagnostics. */
   private[bun] def bundledVersions: Seq[String] = BundledChecksums.keys.toSeq.sorted
 
-  /** Highest `lockfileVersion` each bundled Bun can read. 1.4.0 writes v2; 1.3.14 fails on v2. */
+  /** Highest `lockfileVersion` each bundled Bun can read. 1.4.x writes v2; 1.3.14 fails on v2. */
   private val SupportedLockfileVersions: Map[String, Int] = Map(
     "1.3.14" -> 1,
-    "1.4.0" -> 2
+    "1.4.0" -> 2,
+    "1.4.1" -> 2
   )
 
   private[bun] def supportedLockfileVersion(bunVersion: String): Option[Int] =
diff --git a/millbun/src/mill/javascriptlib/bun/BunTypeScriptModule.scala b/millbun/src/mill/javascriptlib/bun/BunTypeScriptModule.scala
index fbafe14..f1e699d 100644
--- a/millbun/src/mill/javascriptlib/bun/BunTypeScriptModule.scala
+++ b/millbun/src/mill/javascriptlib/bun/BunTypeScriptModule.scala
@@ -66,9 +66,14 @@ trait BunTypeScriptModule extends TypeScriptModule with BunToolchainModule with
   /** Bun ambient types used for bun-targeted Bun builds.
     *
     * `@types/bun` is published in lockstep with Bun itself, so this tracks [[bunVersion]] by
-    * default and the two cannot drift.
+    * default. The one exception is the plugin's own default Bun, which pairs with
+    * [[BunToolchainModule.DefaultBunTypesVersion]] — npm can lag a Bun release by a day or two,
+    * and the shipped default must never 404 on release day.
     */
-  def bunTypesVersion: T[String] = Task { bunVersion() }
+  def bunTypesVersion: T[String] = Task {
+    if (bunVersion() == BunToolchainModule.DefaultBunVersion) BunToolchainModule.DefaultBunTypesVersion
+    else bunVersion()
+  }
 
   /** Ambient runtime types aligned to the configured Bun target. */
   protected def ambientTypeDeps: T[Seq[String]] = Task {
diff --git a/millbun/test/src/mill/bun/BunToolchainTests.scala b/millbun/test/src/mill/bun/BunToolchainTests.scala
index 3393669..fa7c539 100644
--- a/millbun/test/src/mill/bun/BunToolchainTests.scala
+++ b/millbun/test/src/mill/bun/BunToolchainTests.scala
@@ -84,7 +84,7 @@ object BunToolchainTests extends TestSuite:
         assert(checksum.exists(_.matches("[0-9a-f]{64}")))
 
     test("pins the versions the docs and CI claim"):
-      assert(BunToolchainModule.bundledVersions == Seq("1.3.14", "1.4.0"))
+      assert(BunToolchainModule.bundledVersions == Seq("1.3.14", "1.4.0", "1.4.1"))
       // The default must be one we ship checksums for, or the managed path cannot work offline.
       assert(BunToolchainModule.bundledVersions.contains(BunToolchainModule.DefaultBunVersion))