diff --git a/buildfile/src/main/scala/sbt/internal/Eval.scala b/buildfile/src/main/scala/sbt/internal/Eval.scala
index 4d15adc76..0a65c79c1 100644
--- a/buildfile/src/main/scala/sbt/internal/Eval.scala
+++ b/buildfile/src/main/scala/sbt/internal/Eval.scala
@@ -6,6 +6,7 @@ import dotty.tools.dotc.ast.tpd
 import dotty.tools.dotc.CompilationUnit
 import dotty.tools.dotc.core.Contexts.{ atPhase, Context }
 import dotty.tools.dotc.core.{ Flags, NameKinds, Names, Phases, Symbols, Types }
+import dotty.tools.dotc.core.Periods.Period
 import dotty.tools.dotc.Driver
 import dotty.tools.dotc.Run
 import dotty.tools.dotc.util.SourceFile
@@ -70,6 +71,7 @@ class Eval(
       case Some((_, ctx)) => ctx
       case _              => sys.error(s"initialization failed for $options")
     val compileCtx2 = compileCtx1.fresh
+      .setPeriod(Period(2, 1)) // RunId 2 is the actually the first one in the compiler
       .setSetting(
         compileCtx1.settings.outputDir,
         outputDir
@@ -194,7 +196,12 @@ class Eval(
       override def extraHash: String = extraHash0
 
     val inter = evalCommon[Seq[String]](definitions.map(_._1), imports, tpeName = Some(""), ev)
-    EvalDefinitions(inter.loader, inter.generated, inter.enclosingModule, inter.extra.reverse)
+    EvalDefinitions(
+      inter.loader,
+      inter.generated,
+      inter.enclosingModule,
+      inter.extra.reverse.distinct
+    )
 
   end evalDefinitions
 
diff --git a/contributing-docs/05_scripted_tests.md b/contributing-docs/05_scripted_tests.md
index a7b65efb1..0a3306e71 100644
--- a/contributing-docs/05_scripted_tests.md
+++ b/contributing-docs/05_scripted_tests.md
@@ -28,7 +28,7 @@ Create an initial build in `something`. Like a real build using sbt. I'm sure yo
 
 ```scala
 name := "foo"
-scalaVersion := "3.7.4"
+scalaVersion := "3.8.1"
 ```
 
 I also have `Hello.scala`:
@@ -107,7 +107,7 @@ import scala.sys.process.Process
 lazy val check = taskKey[Unit]("check")
 
 name := "foo"
-scalaVersion := "3.7.4"
+scalaVersion := "3.8.1"
 check := {
   val pkg = (Compile / packageBin).value
   val conv = fileConverter.value
diff --git a/contributing-docs/06_manual_tests.md b/contributing-docs/06_manual_tests.md
index aed374f95..0df7223d4 100644
--- a/contributing-docs/06_manual_tests.md
+++ b/contributing-docs/06_manual_tests.md
@@ -22,7 +22,7 @@ $ sbt --server
 
 ### Clearing out boot and local cache
 
-sbt consists of lots of JAR files. When running sbt locally, these JAR artifacts are cached in the `boot` directory under `$HOME/.sbt/boot/scala-3.7.4/org.scala-sbt/sbt/2.0.0-RC8-bin-SNAPSHOT` directory.
+sbt consists of lots of JAR files. When running sbt locally, these JAR artifacts are cached in the `boot` directory under `$HOME/.sbt/boot/scala-3.8.1/org.scala-sbt/sbt/2.0.0-RC8-bin-SNAPSHOT` directory (The Scala version and sbt version part changes).
 
 In order to see a change you've made to sbt's source code, this cache MUST be cleared. To clear this out, from the sbt shell in your application run:
 
diff --git a/launcher-package/citest/build.sbt b/launcher-package/citest/build.sbt
index f623c52dc..571f71996 100644
--- a/launcher-package/citest/build.sbt
+++ b/launcher-package/citest/build.sbt
@@ -3,7 +3,7 @@ lazy val check2 = taskKey[Unit]("")
 
 lazy val root = (project in file("."))
   .settings(
-    scalaVersion := "3.7.3",
+    scalaVersion := "3.8.1",
     name := "Hello",
     libraryDependencies += "com.eed3si9n.verify" %% "verify" % "1.0.0" % Test,
     testFrameworks += new TestFramework("verify.runner.Framework"),
diff --git a/lm-coursier/src/test/scala/lmcoursier/LockFileSpec.scala b/lm-coursier/src/test/scala/lmcoursier/LockFileSpec.scala
index b3effa28a..eb35c2f37 100644
--- a/lm-coursier/src/test/scala/lmcoursier/LockFileSpec.scala
+++ b/lm-coursier/src/test/scala/lmcoursier/LockFileSpec.scala
@@ -38,7 +38,7 @@ class LockFileSpec extends AnyFunSuite {
       ),
       metadata = LockFileMetadata(
         sbtVersion = "2.0.0",
-        scalaVersion = Some("3.7.4")
+        scalaVersion = Some("3.8.1")
       )
     )
 
@@ -59,7 +59,7 @@ class LockFileSpec extends AnyFunSuite {
       assert(readData.configurations.head.dependencies.head.organization == "org.scala-lang")
       assert(readData.configurations.head.dependencies.head.version == "2.13.16")
       assert(readData.metadata.sbtVersion == "2.0.0")
-      assert(readData.metadata.scalaVersion == Some("3.7.4"))
+      assert(readData.metadata.scalaVersion == Some("3.8.1"))
     }
   }
 
diff --git a/main/src/main/scala/sbt/PluginCross.scala b/main/src/main/scala/sbt/PluginCross.scala
index c017e685c..bd0b0e1e7 100644
--- a/main/src/main/scala/sbt/PluginCross.scala
+++ b/main/src/main/scala/sbt/PluginCross.scala
@@ -102,7 +102,7 @@ private[sbt] object PluginCross {
       case VersionNumber(Seq(0, 12, _*), _, _) => "2.9.2"
       case VersionNumber(Seq(0, 13, _*), _, _) => "2.10.7"
       case VersionNumber(Seq(1, 0, _*), _, _)  => "2.12.21"
-      case VersionNumber(Seq(2, _*), _, _)     => "3.7.4"
+      case VersionNumber(Seq(2, _*), _, _)     => "3.8.1"
       case _                                   => sys.error(s"Unsupported sbt binary version: $sv")
     }
 }
diff --git a/project/Dependencies.scala b/project/Dependencies.scala
index 5c133d84b..f2a46e52d 100644
--- a/project/Dependencies.scala
+++ b/project/Dependencies.scala
@@ -4,7 +4,7 @@ import Keys.*
 object Dependencies {
   // WARNING: Please Scala update versions in PluginCross.scala too
   val scala213 = "2.13.16"
-  val scala3 = "3.8.0"
+  val scala3 = "3.8.1"
   val scala212 = "2.12.21"
   val checkPluginCross = settingKey[Unit]("Make sure scalaVersion match up")
   val baseScalaVersion = scala3
@@ -12,8 +12,8 @@ object Dependencies {
     sys.env.get("BUILD_VERSION") orElse sys.props.get("sbt.build.version")
 
   // sbt modules
-  val ioVersion = nightlyVersion.getOrElse("2.0.0-M1")
-  val zincVersion = nightlyVersion.getOrElse("2.0.0-M12")
+  val ioVersion = nightlyVersion.getOrElse("1.10.5")
+  val zincVersion = nightlyVersion.getOrElse("2.0.0-M13")
 
   private val sbtIO = "org.scala-sbt" %% "io" % ioVersion
 
diff --git a/sbt-app/src/sbt-test/cache/cached-compile/build.sbt b/sbt-app/src/sbt-test/cache/cached-compile/build.sbt
index 4097d53bc..187268689 100644
--- a/sbt-app/src/sbt-test/cache/cached-compile/build.sbt
+++ b/sbt-app/src/sbt-test/cache/cached-compile/build.sbt
@@ -5,7 +5,7 @@ lazy val checkMiss = inputKey[Unit]("")
 
 Global / localCacheDirectory := baseDirectory.value / "diskcache"
 
-scalaVersion := "3.7.3"
+scalaVersion := "3.8.1"
 checkMiss := {
   val expected: Int = (Space ~> NatBasic).parsed
   val s = streams.value
diff --git a/sbt-app/src/sbt-test/cache/cached-test/build.sbt b/sbt-app/src/sbt-test/cache/cached-test/build.sbt
index 981eeef7a..292afd055 100644
--- a/sbt-app/src/sbt-test/cache/cached-test/build.sbt
+++ b/sbt-app/src/sbt-test/cache/cached-test/build.sbt
@@ -5,7 +5,7 @@ lazy val verify = "com.eed3si9n.verify" %% "verify" % "1.0.0"
 
 Global / localCacheDirectory := baseDirectory.value / "diskcache"
 
-scalaVersion := "3.7.3"
+scalaVersion := "3.8.1"
 libraryDependencies += verify % Test
 testFrameworks += new TestFramework("verify.runner.Framework")
 
diff --git a/sbt-app/src/sbt-test/nio/clean-symlinks/build.sbt b/sbt-app/src/sbt-test/nio/clean-symlinks/build.sbt
index 019aa7e78..bea44bc5c 100644
--- a/sbt-app/src/sbt-test/nio/clean-symlinks/build.sbt
+++ b/sbt-app/src/sbt-test/nio/clean-symlinks/build.sbt
@@ -2,7 +2,7 @@ import java.nio.file.Files
 
 name := "clean-symlinks-test"
 
-scalaVersion := "3.7.3"
+scalaVersion := "3.8.1"
 
 TaskKey[Unit]("createSymlinkedDirectory") := {
   IO.createDirectory(target.value)
diff --git a/sbt-app/src/sbt-test/nio/clean-symlinks/test b/sbt-app/src/sbt-test/nio/clean-symlinks/test
index 1f5f2141c..2b2632131 100644
--- a/sbt-app/src/sbt-test/nio/clean-symlinks/test
+++ b/sbt-app/src/sbt-test/nio/clean-symlinks/test
@@ -1,9 +1,9 @@
 > createSymlinkedDirectory
 
-$ exists target/out/jvm/scala-3.7.3/clean-symlinks-test/foo/bar
+$ exists target/out/jvm/scala-3.8.1/clean-symlinks-test/foo/bar
 $ exists foo/bar
 
 > clean
 
-$ absent target/out/jvm/scala-3.7.3/clean-symlinks-test/foo
+$ absent target/out/jvm/scala-3.8.1/clean-symlinks-test/foo
 $ exists foo/bar
diff --git a/sbt-app/src/sbt-test/plugins/auto-plugins-minimal/build.sbt b/sbt-app/src/sbt-test/plugins/auto-plugins-minimal/build.sbt
index 36fecfec8..427b3211d 100644
--- a/sbt-app/src/sbt-test/plugins/auto-plugins-minimal/build.sbt
+++ b/sbt-app/src/sbt-test/plugins/auto-plugins-minimal/build.sbt
@@ -1,4 +1,4 @@
-scalaVersion := "3.7.4"
+scalaVersion := "3.8.1"
 
 organization := "com.example"
 
diff --git a/sbt-app/src/sbt-test/plugins/pgp/build.sbt b/sbt-app/src/sbt-test/plugins/pgp/build.sbt
index cd34a40db..9e6b3a95c 100644
--- a/sbt-app/src/sbt-test/plugins/pgp/build.sbt
+++ b/sbt-app/src/sbt-test/plugins/pgp/build.sbt
@@ -1 +1 @@
-scalaVersion := "3.7.3"
+scalaVersion := "3.8.1"
diff --git a/sbt-app/src/sbt-test/plugins/pgp/project/plugins.sbt b/sbt-app/src/sbt-test/plugins/pgp/project/plugins.sbt
index ef28616fc..65b64759c 100644
--- a/sbt-app/src/sbt-test/plugins/pgp/project/plugins.sbt
+++ b/sbt-app/src/sbt-test/plugins/pgp/project/plugins.sbt
@@ -1,2 +1,2 @@
 // addSbtPlugin("com.github.sbt" % "sbt-pgp" % "2.3.1")
-libraryDependencies += Defaults.sbtPluginExtra("com.github.sbt" % "sbt-pgp" % "2.3.1", "2", "3.7.3")
+libraryDependencies += Defaults.sbtPluginExtra("com.github.sbt" % "sbt-pgp" % "2.3.1", "2", "3.8.1")
diff --git a/sbt-app/src/sbt-test/plugins/plugin-cross/build.sbt b/sbt-app/src/sbt-test/plugins/plugin-cross/build.sbt
index e85042f75..040e76e0b 100644
--- a/sbt-app/src/sbt-test/plugins/plugin-cross/build.sbt
+++ b/sbt-app/src/sbt-test/plugins/plugin-cross/build.sbt
@@ -19,4 +19,4 @@ lazy val plugin = (projectMatrix in file("plugin"))
         case _      => "2.0.0-RC3"
     },
   )
-  .jvmPlatform(scalaVersions = Seq("3.7.3", "2.12.21"))
+  .jvmPlatform(scalaVersions = Seq("3.8.1", "2.12.21"))
diff --git a/sbt-app/src/sbt-test/plugins/sbt-native-packager/build.sbt b/sbt-app/src/sbt-test/plugins/sbt-native-packager/build.sbt
index a0c3a463d..a2b6508a9 100644
--- a/sbt-app/src/sbt-test/plugins/sbt-native-packager/build.sbt
+++ b/sbt-app/src/sbt-test/plugins/sbt-native-packager/build.sbt
@@ -1,4 +1,4 @@
-ThisBuild / scalaVersion := "3.7.4"
+ThisBuild / scalaVersion := "3.8.1"
 
 name := "hello"
 enablePlugins(JavaAppPackaging)
@@ -6,7 +6,7 @@ enablePlugins(JavaAppPackaging)
 lazy val check = taskKey[Unit]("")
 
 check := {
-  val cmd = "target/out/jvm/scala-3.7.4/hello/universal/stage/bin/hello"
+  val cmd = "target/out/jvm/scala-3.8.1/hello/universal/stage/bin/hello"
   val cmd0 =
     if (sys.props("os.name").toLowerCase(java.util.Locale.ROOT).contains("windows"))
       cmd + ".bat"
diff --git a/sbt-app/src/sbt-test/plugins/sbt-native-packager/project/plugins.sbt b/sbt-app/src/sbt-test/plugins/sbt-native-packager/project/plugins.sbt
index 18b2ee30c..8340a04be 100644
--- a/sbt-app/src/sbt-test/plugins/sbt-native-packager/project/plugins.sbt
+++ b/sbt-app/src/sbt-test/plugins/sbt-native-packager/project/plugins.sbt
@@ -1,4 +1,4 @@
 ThisBuild / libraryDependencySchemes += "org.scala-lang.modules" %% "scala-xml" % VersionScheme.Always
 
 // addSbtPlugin("com.typesafe.sbt" % "sbt-native-packager" % "1.3.20")
-libraryDependencies += Defaults.sbtPluginExtra("com.github.sbt" % "sbt-native-packager" % "1.11.4", "2", "3.7.3")
+libraryDependencies += Defaults.sbtPluginExtra("com.github.sbt" % "sbt-native-packager" % "1.11.4", "2", "3.8.1")
diff --git a/sbt-app/src/sbt-test/project-load/werror/build.sbt b/sbt-app/src/sbt-test/project-load/werror/build.sbt
index 84a4df0dd..6ccb968d3 100644
--- a/sbt-app/src/sbt-test/project-load/werror/build.sbt
+++ b/sbt-app/src/sbt-test/project-load/werror/build.sbt
@@ -1,4 +1,4 @@
-scalaVersion := "3.7.4"
+scalaVersion := "3.8.1"
 
 @deprecated
 def foo = true
diff --git a/sbt-app/src/sbt-test/project-load/werror/changes/build.sbt b/sbt-app/src/sbt-test/project-load/werror/changes/build.sbt
index db42926ed..ab34113fe 100644
--- a/sbt-app/src/sbt-test/project-load/werror/changes/build.sbt
+++ b/sbt-app/src/sbt-test/project-load/werror/changes/build.sbt
@@ -1,4 +1,4 @@
-scalaVersion := "3.7.4"
+scalaVersion := "3.8.1"
 
 @deprecated
 def foo = true
diff --git a/sbt-app/src/sbt-test/project-matrix/full/build.sbt b/sbt-app/src/sbt-test/project-matrix/full/build.sbt
index 804759a5b..414ee402f 100644
--- a/sbt-app/src/sbt-test/project-matrix/full/build.sbt
+++ b/sbt-app/src/sbt-test/project-matrix/full/build.sbt
@@ -1,5 +1,5 @@
 lazy val scala3_LTS = "3.3.5"
-lazy val scala3_current = "3.7.4"
+lazy val scala3_current = "3.8.1"
 lazy val check = taskKey[Unit]("")
 
 organization := "com.example"
diff --git a/sbt-app/src/sbt-test/project-matrix/full/test b/sbt-app/src/sbt-test/project-matrix/full/test
index 687e928db..ac8c99e9d 100644
--- a/sbt-app/src/sbt-test/project-matrix/full/test
+++ b/sbt-app/src/sbt-test/project-matrix/full/test
@@ -1,4 +1,4 @@
 > packageBin
 $ exists target/**/app_3.3.5-0.1.0-SNAPSHOT.jar
-$ exists target/**/app_3.7.4-0.1.0-SNAPSHOT.jar
+$ exists target/**/app_3.8.1-0.1.0-SNAPSHOT.jar
 > core3_7_4/check
diff --git a/sbt-app/src/sbt-test/project/nested-macro/build.sbt b/sbt-app/src/sbt-test/project/nested-macro/build.sbt
index a74fe9efc..d618b0606 100644
--- a/sbt-app/src/sbt-test/project/nested-macro/build.sbt
+++ b/sbt-app/src/sbt-test/project/nested-macro/build.sbt
@@ -1,6 +1,6 @@
 lazy val a1 = settingKey[Boolean]("")
 
-scalaVersion := "3.7.3"
+scalaVersion := "3.8.1"
 a1 := true
 
 Compile / sourceGenerators += {
diff --git a/sbt-app/src/sbt-test/project/no-delegate/build.sbt b/sbt-app/src/sbt-test/project/no-delegate/build.sbt
index 666b594e7..9e6b3a95c 100644
--- a/sbt-app/src/sbt-test/project/no-delegate/build.sbt
+++ b/sbt-app/src/sbt-test/project/no-delegate/build.sbt
@@ -1 +1 @@
-scalaVersion := "3.7.4"
+scalaVersion := "3.8.1"
diff --git a/sbt-app/src/sbt-test/project/remove/build.sbt b/sbt-app/src/sbt-test/project/remove/build.sbt
index 06ade12b2..b04b02e5b 100644
--- a/sbt-app/src/sbt-test/project/remove/build.sbt
+++ b/sbt-app/src/sbt-test/project/remove/build.sbt
@@ -11,7 +11,7 @@ lazy val intsSetting2 = Def.setting {
   Seq(1, 2, 3)
 }
 
-scalaVersion := "3.7.3"
+scalaVersion := "3.8.1"
 
 intsTask := Seq(1, 2, 3, 4, 5, 6, 7)
 intsTask -= 3
@@ -30,10 +30,10 @@ intsSetting -= intSetting2.value
 intsSetting --= intsSetting2.value
 
 intsFromScalaV := Seq(1, 2, 3, 4, 5, 6, 7)
-intsFromScalaV -= { if scalaVersion.value == "3.7.3" then 3 else 5 }
-intsFromScalaV --= { if scalaVersion.value == "3.7.3" then Seq(1, 2) else Seq(4) }
-intsFromScalaV -= { if scalaVersion.value == "3.7.3" then Option(6) else None }
-intsFromScalaV --= { if scalaVersion.value == "3.7.3" then Option(7) else None }
+intsFromScalaV -= { if scalaVersion.value == "3.8.1" then 3 else 5 }
+intsFromScalaV --= { if scalaVersion.value == "3.8.1" then Seq(1, 2) else Seq(4) }
+intsFromScalaV -= { if scalaVersion.value == "3.8.1" then Option(6) else None }
+intsFromScalaV --= { if scalaVersion.value == "3.8.1" then Option(7) else None }
 
 intsSetSetting := Set(1, 2, 3, 4, 5, 6, 7)
 intsSetSetting -= 3
diff --git a/sbt-app/src/sbt-test/tests/fork-main-resources/build.sbt b/sbt-app/src/sbt-test/tests/fork-main-resources/build.sbt
index 08d15322b..75b852d55 100644
--- a/sbt-app/src/sbt-test/tests/fork-main-resources/build.sbt
+++ b/sbt-app/src/sbt-test/tests/fork-main-resources/build.sbt
@@ -1,6 +1,6 @@
 val scalatest = "org.scalatest" %% "scalatest" % "3.2.19"
 
-scalaVersion := "3.7.3"
+scalaVersion := "3.8.1"
 Test / fork := true
 libraryDependencies += scalatest % Test
 
diff --git a/sbt-app/src/sbt-test/tests/fork2/build.sbt b/sbt-app/src/sbt-test/tests/fork2/build.sbt
index d9c596e82..7239866a8 100644
--- a/sbt-app/src/sbt-test/tests/fork2/build.sbt
+++ b/sbt-app/src/sbt-test/tests/fork2/build.sbt
@@ -1,5 +1,5 @@
 val scalatest = "org.scalatest" %% "scalatest" % "3.2.19"
 
-scalaVersion := "3.7.3"
+scalaVersion := "3.8.1"
 fork := true
 libraryDependencies += scalatest % Test
diff --git a/sbt-app/src/sbt-test/tests/incremental-object-deps/build.sbt b/sbt-app/src/sbt-test/tests/incremental-object-deps/build.sbt
index 8338afdf3..40cd3ad76 100644
--- a/sbt-app/src/sbt-test/tests/incremental-object-deps/build.sbt
+++ b/sbt-app/src/sbt-test/tests/incremental-object-deps/build.sbt
@@ -1,3 +1,3 @@
-scalaVersion := "3.7.3"
+scalaVersion := "3.8.1"
 libraryDependencies += "com.eed3si9n.verify" %% "verify" % "1.0.0" % Test
 testFrameworks += new TestFramework("verify.runner.Framework")
diff --git a/sbt-app/src/sbt-test/tests/t543/build.sbt b/sbt-app/src/sbt-test/tests/t543/build.sbt
index 526570c26..02bdf1a0f 100644
--- a/sbt-app/src/sbt-test/tests/t543/build.sbt
+++ b/sbt-app/src/sbt-test/tests/t543/build.sbt
@@ -6,7 +6,7 @@ val marker = new File("marker")
 val check = TaskKey[Unit]("check", "Check correct error has been returned.")
 val scalatest = "org.scalatest" %% "scalatest" % "3.2.19"
 
-ThisBuild / scalaVersion := "3.7.3"
+ThisBuild / scalaVersion := "3.8.1"
 
 lazy val root = (project in file(".")).
   settings(
diff --git a/server-test/src/server-test/client/build.sbt b/server-test/src/server-test/client/build.sbt
index 60d98fc88..5e7448817 100644
--- a/server-test/src/server-test/client/build.sbt
+++ b/server-test/src/server-test/client/build.sbt
@@ -1,4 +1,4 @@
-scalaVersion := "3.7.3"
+scalaVersion := "3.8.1"
 
 TaskKey[Unit]("willSucceed") := println("success")