diff --git a/.github/workflows/scala.yml b/.github/workflows/scala.yml
index 86bb19c..e7422a4 100644
--- a/.github/workflows/scala.yml
+++ b/.github/workflows/scala.yml
@@ -9,7 +9,15 @@ on:
 jobs:
   build:
 
-    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - os: ubuntu-latest
+            jobtype: 1
+          - os: ubuntu-latest
+            jobtype: 2
+    runs-on: ${{ matrix.os }}
 
     steps:
     - uses: actions/checkout@v5
@@ -21,5 +29,11 @@ jobs:
         cache: sbt
     - name: Install sbt
       uses: sbt/setup-sbt@v1
-    - name: Run tests
-      run: sbt "^ scripted"
+    - name: Build and test
+      if: ${{ matrix.jobtype == 1 }}
+      shell: bash
+      run: sbt -v '++ 2.12.x' scripted
+    - name: Scala 3
+      if: ${{ matrix.jobtype == 2 }}
+      shell: bash
+      run: sbt -v '++ 3.x' 'scripted agent/*'
diff --git a/build.sbt b/build.sbt
index 17d717b..0053822 100644
--- a/build.sbt
+++ b/build.sbt
@@ -2,13 +2,13 @@
  * Copyright © 2016-2017 Lightbend, Inc. <http://www.lightbend.com>
  */
 
-// sbt cross build
-crossSbtVersions := Seq("1.11.4")
-
 // dependencies
 val packagerVersion = "1.11.3"
 val packager19xVersion = "1.9.16"
 
+val scala212 = "2.12.20"
+val scala3 = "3.7.2"
+
 addSbtPlugin(
   "com.github.sbt" % "sbt-native-packager" % packagerVersion % "provided"
 )
@@ -42,6 +42,13 @@ lazy val `sbt-javaagent` = (project.in(file(".")))
   .settings(
     name := "sbt-javaagent",
     organization := "com.github.sbt",
+    crossScalaVersions := Seq(scala212, scala3),
+    scalacOptions ++= {
+      scalaBinaryVersion.value match {
+        case "2.12" => Seq("-Xsource:3")
+        case _      => Nil
+      }
+    },
     scriptedBufferLog := false,
     scriptedLaunchOpts ++= Seq(
       "-Dproject.version=" + version.value,
@@ -51,6 +58,18 @@ lazy val `sbt-javaagent` = (project.in(file(".")))
     scriptedDependencies := {
       (maxwell / publishLocal).value
       publishLocal.value
+    },
+    (pluginCrossBuild / sbtVersion) := {
+      scalaBinaryVersion.value match {
+        case "2.12" => "1.11.6"
+        case _      => "2.0.0-RC4"
+      }
+    },
+    scriptedSbt := {
+      scalaBinaryVersion.value match {
+        case "2.12" => "1.11.6"
+        case _      => (pluginCrossBuild / sbtVersion).value
+      }
     }
   )
 
diff --git a/src/main/scala-2.12/AgentModule.scala b/src/main/scala-2.12/AgentModule.scala
new file mode 100644
index 0000000..0002868
--- /dev/null
+++ b/src/main/scala-2.12/AgentModule.scala
@@ -0,0 +1,14 @@
+package com.lightbend.sbt.javaagent
+
+import sbt.*
+import scala.language.implicitConversions
+
+case class AgentScope(compile: Boolean = false, test: Boolean = false, run: Boolean = false, dist: Boolean = true)
+
+case class AgentModule(name: String, module: ModuleID, scope: AgentScope, arguments: String)
+
+case class ResolvedAgent(agent: AgentModule, artifact: File)
+
+object AgentModule {
+  implicit def moduleToAgentModule(module: ModuleID): AgentModule = JavaAgent(module)
+}
diff --git a/src/main/scala-2.12/PluginCompat.scala b/src/main/scala-2.12/PluginCompat.scala
new file mode 100644
index 0000000..0a11a25
--- /dev/null
+++ b/src/main/scala-2.12/PluginCompat.scala
@@ -0,0 +1,25 @@
+package com.lightbend.sbt.javaagent
+
+import sbt.*
+import java.nio.file.{ Path => NioPath }
+import xsbti.FileConverter
+
+private[javaagent] object PluginCompat {
+  type FileRef = java.io.File
+  type Out = java.io.File
+
+  def toNioPath(a: Attributed[File])(implicit conv: FileConverter): NioPath =
+    a.data.toPath()
+  def toFile(a: Attributed[File])(implicit conv: FileConverter): File =
+    a.data
+  def toNioPaths(cp: Seq[Attributed[File]])(implicit conv: FileConverter): Vector[NioPath] =
+    cp.map(_.data.toPath()).toVector
+  def toFiles(cp: Seq[Attributed[File]])(implicit conv: FileConverter): Vector[File] =
+    cp.map(_.data).toVector
+  def toFileRef(a: File)(implicit conv: FileConverter): File = a
+
+  // This adds `Def.uncached(...)`
+  implicit class DefOp(singleton: Def.type) {
+    def uncached[A1](a: A1): A1 = a
+  }
+}
diff --git a/src/main/scala-3/AgentModule.scala b/src/main/scala-3/AgentModule.scala
new file mode 100644
index 0000000..d326e87
--- /dev/null
+++ b/src/main/scala-3/AgentModule.scala
@@ -0,0 +1,15 @@
+package com.lightbend.sbt.javaagent
+
+import sbt.*
+import scala.language.implicitConversions
+
+case class AgentScope(compile: Boolean = false, test: Boolean = false, run: Boolean = false, dist: Boolean = true)
+
+case class AgentModule(name: String, module: ModuleID, scope: AgentScope, arguments: String)
+
+case class ResolvedAgent(agent: AgentModule, artifact: File)
+
+object AgentModule {
+  given Conversion[ModuleID, AgentModule] with
+    def apply(module: ModuleID): AgentModule = JavaAgent(module)
+}
diff --git a/src/main/scala-3/PluginCompat.scala b/src/main/scala-3/PluginCompat.scala
new file mode 100644
index 0000000..1f245ea
--- /dev/null
+++ b/src/main/scala-3/PluginCompat.scala
@@ -0,0 +1,21 @@
+package com.lightbend.sbt.javaagent
+
+import java.nio.file.{ Path => NioPath }
+import sbt.*
+import xsbti.{ FileConverter, HashedVirtualFileRef, VirtualFile }
+
+private[javaagent] object PluginCompat:
+  type FileRef = HashedVirtualFileRef
+  type Out = VirtualFile
+
+  def toNioPath(a: Attributed[HashedVirtualFileRef])(using conv: FileConverter): NioPath =
+    conv.toPath(a.data)
+  inline def toFile(a: Attributed[HashedVirtualFileRef])(using conv: FileConverter): File =
+    toNioPath(a).toFile()
+  def toNioPaths(cp: Seq[Attributed[HashedVirtualFileRef]])(using conv: FileConverter): Vector[NioPath] =
+    cp.map(toNioPath).toVector
+  inline def toFiles(cp: Seq[Attributed[HashedVirtualFileRef]])(using conv: FileConverter): Vector[File] =
+    toNioPaths(cp).map(_.toFile())
+  def toFileRef(a: File)(using conv: FileConverter): HashedVirtualFileRef =
+    conv.toVirtualFile(a.toPath())
+end PluginCompat
diff --git a/src/main/scala/com/lightbend/sbt/javaagent/JavaAgent.scala b/src/main/scala/com/lightbend/sbt/javaagent/JavaAgent.scala
index 2b70611..35a05f6 100644
--- a/src/main/scala/com/lightbend/sbt/javaagent/JavaAgent.scala
+++ b/src/main/scala/com/lightbend/sbt/javaagent/JavaAgent.scala
@@ -4,8 +4,10 @@
 
 package com.lightbend.sbt.javaagent
 
-import sbt._
-import sbt.Keys._
+import sbt.*
+import sbt.Keys.*
+import xsbti.FileConverter
+import PluginCompat.{ *, given }
 
 /**
  * Plugin for adding Java agents to projects in a general way.
@@ -17,22 +19,13 @@ object JavaAgent extends JavaAgent {
 
   object JavaAgentKeys {
     val javaAgents = settingKey[Seq[AgentModule]]("Java agent modules enabled for this project.")
+
+    @transient
     val resolvedJavaAgents = taskKey[Seq[ResolvedAgent]]("Java agent modules with resolved artifacts.")
   }
 
   val AgentConfig = config("javaagent").hide
 
-  case class AgentScope(compile: Boolean = false, test: Boolean = false, run: Boolean = false, dist: Boolean = true)
-
-  case class AgentModule(name: String, module: ModuleID, scope: AgentScope, arguments: String)
-
-  case class ResolvedAgent(agent: AgentModule, artifact: File)
-
-  object AgentModule {
-    import scala.language.implicitConversions
-    implicit def moduleToAgentModule(module: ModuleID): AgentModule = JavaAgent(module)
-  }
-
   /**
    * Create an agent module from a module dependency.
    * Scope is also derived from the given module configuration.
@@ -69,7 +62,11 @@ class JavaAgent extends AutoPlugin {
     Test/fork := enableFork(Test/fork, _.scope.test).value,
     run/javaOptions ++= agentOptions(_.agent.scope.run).value,
     Test/javaOptions ++= agentOptions(_.agent.scope.test).value,
-    Test/fullClasspath := filterAgents((Test/fullClasspath).value, resolvedJavaAgents.value)
+    Test/fullClasspath := Def.uncached {
+      val conv = fileConverter.value
+      implicit val conv0: xsbti.FileConverter = conv
+      filterAgents((Test/fullClasspath).value, resolvedJavaAgents.value)
+    }
   )
 
   private def resolveAgents = Def.task[Seq[ResolvedAgent]] {
@@ -102,8 +99,9 @@ class JavaAgent extends AutoPlugin {
     }
   }
 
-  def filterAgents(classpath: Classpath, resolvedAgents: Seq[ResolvedAgent]): Classpath = {
+  def filterAgents(classpath: Classpath, resolvedAgents: Seq[ResolvedAgent])(implicit conv: FileConverter): Classpath = {
     val agents = resolvedAgents.map(resolved => resolved.artifact.absolutePath)
-    classpath.filter(aFile => !agents.contains(aFile.data.getAbsolutePath))
+    classpath
+      .filter(entry => !agents.contains(PluginCompat.toFile(entry).getAbsolutePath))
   }
 }
diff --git a/src/main/scala/com/lightbend/sbt/javaagent/JavaAgentPackaging.scala b/src/main/scala/com/lightbend/sbt/javaagent/JavaAgentPackaging.scala
index 63ad770..8f42cb5 100644
--- a/src/main/scala/com/lightbend/sbt/javaagent/JavaAgentPackaging.scala
+++ b/src/main/scala/com/lightbend/sbt/javaagent/JavaAgentPackaging.scala
@@ -4,8 +4,8 @@
 
 package com.lightbend.sbt.javaagent
 
-import sbt._
-import sbt.Keys._
+import sbt.*
+import sbt.Keys.*
 import com.typesafe.sbt.packager.universal.UniversalPlugin.autoImport.Universal
 import java.io.File
 
@@ -24,7 +24,11 @@ object JavaAgentPackaging extends AutoPlugin {
   override def projectSettings = {
     import com.typesafe.sbt.packager.{ Keys => PackagerKeys }
     Seq(
-      Universal / mappings ++= agentMappings.value.map(m => m._1 -> m._2),
+      Universal / mappings ++= {
+        val conv = fileConverter.value
+        implicit val conv0: xsbti.FileConverter = conv
+        agentMappings.value.map(m => PluginCompat.toFileRef(m._1) -> m._2)
+      },
       PackagerKeys.bashScriptExtraDefines ++= agentBashScriptOptions.value,
       PackagerKeys.batScriptExtraDefines ++= agentBatScriptOptions.value
     )
diff --git a/src/sbt-test/agent/confs/build.sbt b/src/sbt-test/agent-1/confs/build.sbt
similarity index 100%
rename from src/sbt-test/agent/confs/build.sbt
rename to src/sbt-test/agent-1/confs/build.sbt
diff --git a/src/sbt-test/agent/confs/project/plugins.sbt b/src/sbt-test/agent-1/confs/project/plugins.sbt
similarity index 100%
rename from src/sbt-test/agent/confs/project/plugins.sbt
rename to src/sbt-test/agent-1/confs/project/plugins.sbt
diff --git a/src/sbt-test/agent/confs/src/main/scala/Main.scala b/src/sbt-test/agent-1/confs/src/main/scala/Main.scala
similarity index 100%
rename from src/sbt-test/agent/confs/src/main/scala/Main.scala
rename to src/sbt-test/agent-1/confs/src/main/scala/Main.scala
diff --git a/src/sbt-test/agent/confs/src/test/scala/Test.scala b/src/sbt-test/agent-1/confs/src/test/scala/Test.scala
similarity index 100%
rename from src/sbt-test/agent/confs/src/test/scala/Test.scala
rename to src/sbt-test/agent-1/confs/src/test/scala/Test.scala
diff --git a/src/sbt-test/agent/confs/test b/src/sbt-test/agent-1/confs/test
similarity index 100%
rename from src/sbt-test/agent/confs/test
rename to src/sbt-test/agent-1/confs/test
diff --git a/src/sbt-test/agent/confs/test.sbt b/src/sbt-test/agent-1/confs/test.sbt
similarity index 100%
rename from src/sbt-test/agent/confs/test.sbt
rename to src/sbt-test/agent-1/confs/test.sbt
diff --git a/src/sbt-test/agent/dist_1.9.x/build.sbt b/src/sbt-test/agent-1/dist_1.9.x/build.sbt
similarity index 100%
rename from src/sbt-test/agent/dist_1.9.x/build.sbt
rename to src/sbt-test/agent-1/dist_1.9.x/build.sbt
diff --git a/src/sbt-test/agent/dist_1.9.x/project/plugins.sbt b/src/sbt-test/agent-1/dist_1.9.x/project/plugins.sbt
similarity index 100%
rename from src/sbt-test/agent/dist_1.9.x/project/plugins.sbt
rename to src/sbt-test/agent-1/dist_1.9.x/project/plugins.sbt
diff --git a/src/sbt-test/agent/dist_1.9.x/src/main/scala/Main.scala b/src/sbt-test/agent-1/dist_1.9.x/src/main/scala/Main.scala
similarity index 100%
rename from src/sbt-test/agent/dist_1.9.x/src/main/scala/Main.scala
rename to src/sbt-test/agent-1/dist_1.9.x/src/main/scala/Main.scala
diff --git a/src/sbt-test/agent/dist_1.9.x/test b/src/sbt-test/agent-1/dist_1.9.x/test
similarity index 100%
rename from src/sbt-test/agent/dist_1.9.x/test
rename to src/sbt-test/agent-1/dist_1.9.x/test
diff --git a/src/sbt-test/agent/dist_1.9.x/test.sbt b/src/sbt-test/agent-1/dist_1.9.x/test.sbt
similarity index 100%
rename from src/sbt-test/agent/dist_1.9.x/test.sbt
rename to src/sbt-test/agent-1/dist_1.9.x/test.sbt
diff --git a/src/sbt-test/agent/test/build.sbt b/src/sbt-test/agent-1/test/build.sbt
similarity index 100%
rename from src/sbt-test/agent/test/build.sbt
rename to src/sbt-test/agent-1/test/build.sbt
diff --git a/src/sbt-test/agent/test/project/plugins.sbt b/src/sbt-test/agent-1/test/project/plugins.sbt
similarity index 100%
rename from src/sbt-test/agent/test/project/plugins.sbt
rename to src/sbt-test/agent-1/test/project/plugins.sbt
diff --git a/src/sbt-test/agent/test/src/test/scala/Test.scala b/src/sbt-test/agent-1/test/src/test/scala/Test.scala
similarity index 100%
rename from src/sbt-test/agent/test/src/test/scala/Test.scala
rename to src/sbt-test/agent-1/test/src/test/scala/Test.scala
diff --git a/src/sbt-test/agent/test/test b/src/sbt-test/agent-1/test/test
similarity index 100%
rename from src/sbt-test/agent/test/test
rename to src/sbt-test/agent-1/test/test
diff --git a/src/sbt-test/agent/test/test.sbt b/src/sbt-test/agent-1/test/test.sbt
similarity index 100%
rename from src/sbt-test/agent/test/test.sbt
rename to src/sbt-test/agent-1/test/test.sbt
diff --git a/src/sbt-test/agent/compile/build.sbt b/src/sbt-test/agent/compile/build.sbt
index 71c47b0..42be0e5 100644
--- a/src/sbt-test/agent/compile/build.sbt
+++ b/src/sbt-test/agent/compile/build.sbt
@@ -3,4 +3,4 @@ lazy val agentCompile =
 
 javaAgents += "sbt.javaagent.test" % "maxwell" % sys.props(
   "project.version"
-) % "compile"
+) % Compile