diff --git a/.github/workflows/build.yaml b/.github/workflows/build.yaml
index 320758a..85c18f1 100644
--- a/.github/workflows/build.yaml
+++ b/.github/workflows/build.yaml
@@ -57,3 +57,38 @@ jobs:
       if: matrix.java == 23
       run: |
         sbt core/doc
+
+  integration:
+    runs-on: ubuntu-latest
+    name: Multi-Release JAR Integration Test
+    steps:
+    - uses: actions/checkout@v4
+    - name: Set up Java
+      uses: actions/setup-java@v4
+      with:
+        java-version: |
+          21
+          22
+        distribution: 'temurin'
+        cache: 'sbt'
+    - name: Set up sbt
+      uses: sbt/setup-sbt@v1
+    - name: Run tests
+      run: |
+        # Build multi-release override classes on Java 22
+        PATH=$JAVA_HOME_22_X64/bin:$PATH JAVA_HOME=$JAVA_HOME_22_X64 sbt \
+          core/compile
+        cp -r core/target/classes override-core-j22
+        # Build jar on Java 21 with --enable-preview and include Java 22 overrides
+        PATH=$JAVA_HOME_21_X64/bin:$PATH JAVA_HOME=$JAVA_HOME_21_X64 JAVA_OPTS=--enable-preview \
+          OVERRIDE_CORE_J22=`realpath override-core-j22` sbt \
+          core/clean \
+          core/packageBin
+        # Run tests with multi-release jar
+        cp `realpath core/target/perfio-*.jar` override-test.jar
+        PATH=$JAVA_HOME_21_X64/bin:$PATH JAVA_HOME=$JAVA_HOME_21_X64 JAVA_OPTS=--enable-preview \
+          OVERRIDE_TEST_JAR=`realpath override-test.jar` sbt \
+          test/test
+        PATH=$JAVA_HOME_22_X64/bin:$PATH JAVA_HOME=$JAVA_HOME_22_X64 \
+          OVERRIDE_TEST_JAR=`realpath override-test.jar` sbt \
+          test/test
diff --git a/.github/workflows/release.yaml b/.github/workflows/release.yaml
index 71a6545..cd4ac9a 100644
--- a/.github/workflows/release.yaml
+++ b/.github/workflows/release.yaml
@@ -23,6 +23,7 @@ jobs:
       with:
         java-version: |
           21
+          22
           23
         distribution: 'temurin'
         cache: 'sbt'
@@ -42,9 +43,15 @@ jobs:
         SONATYPE_USER: ${{ secrets.SONATYPE_USER }}
         SONATYPE_PASSWORD: ${{ secrets.SONATYPE_PASSWORD }}
       run: |
-        # Publish binaries with Java 21 (because we can't use --enable-preview for 21 from 23)
-        PATH=$JAVA_HOME_21_X64/bin:$PATH JAVA_HOME=$JAVA_HOME_21_X64 JAVA_OPTS=--enable-preview sbt \
+        # Build multi-release override classes with Java 22
+        PATH=$JAVA_HOME_22_X64/bin:$PATH JAVA_HOME=$JAVA_HOME_22_X64 sbt \
+          core/compile
+        cp -r core/target/classes override-core-j22
+        # Publish binaries with Java 21 with --enable-preview and include Java 22 overrides
+        PATH=$JAVA_HOME_21_X64/bin:$PATH JAVA_HOME=$JAVA_HOME_21_X64 JAVA_OPTS=--enable-preview \
+          OVERRIDE_CORE_J22=`realpath override-core-j22` sbt \
           "set core/Compile/packageDoc/publishArtifact := false" \
+          core/clean \
           core/publishSigned
         ls -lR target/sonatype-staging
         # Publish javadoc with Java 23 (because we need Markdown support)
diff --git a/build.sbt b/build.sbt
index abfa47a..3cacd66 100644
--- a/build.sbt
+++ b/build.sbt
@@ -1,5 +1,6 @@
+import java.io.FileInputStream
 import java.nio.file.{Files, Path}
-import scala.jdk.CollectionConverters._
+import scala.jdk.CollectionConverters.*
 
 val PROTOBUF_HOME = sys.env.getOrElse("PROTOBUF_HOME", s"${sys.props("user.home")}/protobuf")
 val protobufVersion = "4.29.0-RC2"
@@ -24,6 +25,9 @@ val compileOpts = Seq(
   "--enable-preview",
 ))
 
+// External jar to use instead of `core` for tests and benchmarks
+val overrideTestJar = sys.env.get("OVERRIDE_TEST_JAR")
+
 javaOptions in Global ++= runtimeOpts
 javacOptions in Global ++= compileOpts
 scalacOptions in Global ++= Seq("-java-output-version", release.toString)
@@ -78,13 +82,47 @@ lazy val core = (project in file("core"))
     crossPaths := false,
     autoScalaLibrary := false,
     name := "perfio",
+    // When building the Java 21 version, add multi-release overrides for preview API classes
+    // by copying them from a previously built Java 22 output directory
+    Compile / packageBin / mappings := {
+      val orig = (Compile / packageBin / mappings).value
+      sys.env.get("OVERRIDE_CORE_J22") match {
+        case Some(j22classes) =>
+          println("Building multi-release jar")
+          val overrides = orig.collect {
+            case (f, s) if s.endsWith(".class") && isPreview(f) =>
+            val nf = new File(j22classes, s)
+            assert(nf.exists())
+            val ns = "META-INF/versions/22/" + s
+            println("  Adding override "+ns)
+            (nf, ns)
+          }
+          orig ++ overrides
+        case None => orig
+      }
+    },
+    (Compile / packageBin) / packageOptions +=
+      Package.ManifestAttributes("Multi-Release" -> "true"),
   )
 
 lazy val scalaApi = (project in file("scalaapi"))
-  .dependsOn(core)
+  .dependsOn(
+    (overrideTestJar match {
+      case Some(_) => Nil
+      case None => Seq(core: ClasspathDep[ProjectReference])
+    }): _*
+  )
   .settings(
     name := "perfio-scala",
     publish / skip := true,
+    (Compile / unmanagedJars) ++= {
+      overrideTestJar match {
+        case Some(j) =>
+          println("Using override test jar "+j)
+          Seq(file(j))
+        case None => Nil
+      }
+    },
   )
 
 lazy val benchUtil = (project in file("bench-util"))
@@ -215,3 +253,11 @@ test_ / Test / javap := {
   val pb = new ProcessBuilder(Seq("javap", "-cp", cp.iterator.map(_.data).mkString(sys.props.getOrElse("path.separator", ":"))) ++ args: _*).inheritIO()
   pb.start().waitFor()
 }
+
+def isPreview(classFile: File): Boolean = {
+  val in = new FileInputStream(classFile)
+  try {
+    val a = in.readNBytes(5)
+    a(4) != 0
+  } finally in.close()
+}