diff --git a/zipline-gradle-plugin/src/main/kotlin/app/cash/zipline/gradle/ZiplineCompileTask.kt b/zipline-gradle-plugin/src/main/kotlin/app/cash/zipline/gradle/ZiplineCompileTask.kt
index e622aa058d..b5af9870d1 100644
--- a/zipline-gradle-plugin/src/main/kotlin/app/cash/zipline/gradle/ZiplineCompileTask.kt
+++ b/zipline-gradle-plugin/src/main/kotlin/app/cash/zipline/gradle/ZiplineCompileTask.kt
@@ -25,6 +25,7 @@ import okio.ByteString.Companion.decodeHex
 import org.gradle.api.DefaultTask
 import org.gradle.api.file.DirectoryProperty
 import org.gradle.api.provider.ListProperty
+import org.gradle.api.provider.MapProperty
 import org.gradle.api.provider.Property
 import org.gradle.api.tasks.Input
 import org.gradle.api.tasks.InputDirectory
@@ -62,6 +63,10 @@ abstract class ZiplineCompileTask : DefaultTask() {
   @get:Input
   abstract val version: Property<String>
 
+  @get:Optional
+  @get:Input
+  abstract val metadata: MapProperty<String, String>
+
   internal fun configure(
     jsProductionTask: JsProductionTask,
     extension: ZiplineExtension,
@@ -79,6 +84,7 @@ abstract class ZiplineCompileTask : DefaultTask() {
     mainModuleId.set(extension.mainModuleId)
     mainFunction.set(extension.mainFunction)
     version.set(extension.version)
+    metadata.set(extension.metadata)
 
     signingKeys.set(
       project.provider {
@@ -111,6 +117,7 @@ abstract class ZiplineCompileTask : DefaultTask() {
       else -> null
     }
     val version = version.orNull
+    val metadata = metadata.orNull ?: mapOf()
 
     if (inputChanges.isIncremental) {
       fun filterByChangeType(filter: (ChangeType) -> Boolean): List<File> {
@@ -128,6 +135,7 @@ abstract class ZiplineCompileTask : DefaultTask() {
         mainModuleId = mainModuleId,
         manifestSigner = manifestSigner,
         version = version,
+        metadata = metadata,
       )
     } else {
       ZiplineCompiler.compile(
@@ -137,6 +145,7 @@ abstract class ZiplineCompileTask : DefaultTask() {
         mainModuleId = mainModuleId,
         manifestSigner = manifestSigner,
         version = version,
+        metadata = metadata,
       )
     }
   }
diff --git a/zipline-gradle-plugin/src/main/kotlin/app/cash/zipline/gradle/ZiplineCompiler.kt b/zipline-gradle-plugin/src/main/kotlin/app/cash/zipline/gradle/ZiplineCompiler.kt
index 879b269aa6..7d721db301 100644
--- a/zipline-gradle-plugin/src/main/kotlin/app/cash/zipline/gradle/ZiplineCompiler.kt
+++ b/zipline-gradle-plugin/src/main/kotlin/app/cash/zipline/gradle/ZiplineCompiler.kt
@@ -46,6 +46,7 @@ internal object ZiplineCompiler {
     mainModuleId: String?,
     manifestSigner: ManifestSigner?,
     version: String?,
+    metadata: Map<String, String>,
   ) {
     val jsFiles = getJsFiles(inputDir.listFiles()!!.asList())
     val modules = compileFilesInParallel(jsFiles, outputDir)
@@ -56,6 +57,7 @@ internal object ZiplineCompiler {
       manifestSigner = manifestSigner,
       modules = modules,
       version = version,
+      metadata = metadata,
     )
   }
 
@@ -68,6 +70,7 @@ internal object ZiplineCompiler {
     mainModuleId: String?,
     manifestSigner: ManifestSigner?,
     version: String?,
+    metadata: Map<String, String>,
   ) {
     val modifiedFileNames = getJsFiles(modifiedFiles).map { it.name }.toSet()
     val removedFileNames = getJsFiles(removedFiles).map { it.name }.toSet()
@@ -95,6 +98,7 @@ internal object ZiplineCompiler {
       manifestSigner = manifestSigner,
       modules = unchangedModules + compiledModules,
       version = version,
+      metadata = metadata,
     )
   }
 
@@ -150,17 +154,19 @@ internal object ZiplineCompiler {
 
   private fun writeManifest(
     outputDir: File,
-    mainFunction: String? = null,
-    mainModuleId: String? = null,
-    manifestSigner: ManifestSigner? = null,
+    mainFunction: String?,
+    mainModuleId: String?,
+    manifestSigner: ManifestSigner?,
     modules: Map<String, ZiplineManifest.Module>,
-    version: String? = null,
+    version: String?,
+    metadata: Map<String, String>,
   ) {
     val unsignedManifest = ZiplineManifest.create(
       modules = modules,
       mainFunction = mainFunction,
       mainModuleId = mainModuleId,
       version = version,
+      metadata = metadata,
     )
 
     val manifest = manifestSigner?.sign(unsignedManifest) ?: unsignedManifest
diff --git a/zipline-gradle-plugin/src/main/kotlin/app/cash/zipline/gradle/ZiplineExtension.kt b/zipline-gradle-plugin/src/main/kotlin/app/cash/zipline/gradle/ZiplineExtension.kt
index 8708d7bda4..5598a5cf4b 100644
--- a/zipline-gradle-plugin/src/main/kotlin/app/cash/zipline/gradle/ZiplineExtension.kt
+++ b/zipline-gradle-plugin/src/main/kotlin/app/cash/zipline/gradle/ZiplineExtension.kt
@@ -17,6 +17,7 @@ package app.cash.zipline.gradle
 
 import app.cash.zipline.loader.SignatureAlgorithmId
 import org.gradle.api.NamedDomainObjectContainer
+import org.gradle.api.provider.MapProperty
 import org.gradle.api.provider.Property
 
 abstract class ZiplineExtension {
@@ -25,6 +26,7 @@ abstract class ZiplineExtension {
   abstract val version: Property<String>
   abstract val signingKeys: NamedDomainObjectContainer<SigningKey>
   abstract val httpServerPort: Property<Int>
+  abstract val metadata: MapProperty<String, String>
 
   abstract class SigningKey(val name: String) {
     abstract val algorithmId: Property<SignatureAlgorithmId>
diff --git a/zipline-gradle-plugin/src/test/kotlin/app/cash/zipline/gradle/ZiplineCompilerTest.kt b/zipline-gradle-plugin/src/test/kotlin/app/cash/zipline/gradle/ZiplineCompilerTest.kt
index 2c0e8995c2..b8e99f75a1 100644
--- a/zipline-gradle-plugin/src/test/kotlin/app/cash/zipline/gradle/ZiplineCompilerTest.kt
+++ b/zipline-gradle-plugin/src/test/kotlin/app/cash/zipline/gradle/ZiplineCompilerTest.kt
@@ -151,6 +151,7 @@ class ZiplineCompilerTest {
       mainModuleId = mainModuleId,
       manifestSigner = null,
       version = null,
+      metadata = mapOf(),
     )
 
     val expectedNumberFiles = if (dirHasSourceMaps) inputDir.listFiles()!!.size / 2 else inputDir.listFiles()!!.size
@@ -182,6 +183,7 @@ class ZiplineCompilerTest {
       removedFiles = removedFiles,
       manifestSigner = null,
       version = null,
+      metadata = mapOf(),
     )
 
     val expectedNumberFiles = inputDir.listFiles()!!.size + addedFiles.size - removedFiles.size
diff --git a/zipline-gradle-plugin/src/test/kotlin/app/cash/zipline/gradle/ZiplinePluginTest.kt b/zipline-gradle-plugin/src/test/kotlin/app/cash/zipline/gradle/ZiplinePluginTest.kt
index 014ff433b8..5781b8dc72 100644
--- a/zipline-gradle-plugin/src/test/kotlin/app/cash/zipline/gradle/ZiplinePluginTest.kt
+++ b/zipline-gradle-plugin/src/test/kotlin/app/cash/zipline/gradle/ZiplinePluginTest.kt
@@ -139,6 +139,26 @@ class ZiplinePluginTest {
     assertThat(ziplineOut.resolve("multipleJsTargets-lib-blue.zipline").exists()).isTrue()
   }
 
+  @Test
+  fun versionAndMetadata() {
+    val projectDir = File("src/test/projects/basic")
+
+    val taskName = ":lib:compileDevelopmentExecutableKotlinJsZipline"
+    val result = createRunner(projectDir, "clean", taskName).build()
+    assertThat(SUCCESS_OUTCOMES)
+      .contains(result.task(taskName)!!.outcome)
+
+    val ziplineOut = projectDir.resolve(
+      "lib/build/compileSync/js/main/developmentExecutable/kotlinZipline",
+    )
+    val manifest = ziplineOut.resolve(manifestFileName)
+    val manifestText = manifest.readText()
+    assertThat(manifestText)
+      .contains(""""version":"1.2.3"""")
+    assertThat(manifestText)
+      .contains(""""metadata":{"build_timestamp":"2023-10-25T12:00:00T"}""")
+  }
+
   @Test
   fun manifestSigning() {
     val projectDir = File("src/test/projects/signing")
diff --git a/zipline-gradle-plugin/src/test/projects/basic/lib/build.gradle.kts b/zipline-gradle-plugin/src/test/projects/basic/lib/build.gradle.kts
index ae15ad69b9..7a2ac22eb6 100644
--- a/zipline-gradle-plugin/src/test/projects/basic/lib/build.gradle.kts
+++ b/zipline-gradle-plugin/src/test/projects/basic/lib/build.gradle.kts
@@ -42,6 +42,8 @@ val launchGreetService by tasks.creating(JavaExec::class) {
 
 zipline {
   mainFunction.set("app.cash.zipline.tests.launchGreetService")
+  version.set("1.2.3")
+  metadata.put("build_timestamp", "2023-10-25T12:00:00T")
 }
 
 plugins.withType<YarnPlugin> {
diff --git a/zipline-gradle-plugin/src/test/projects/signing/lib/build.gradle.kts b/zipline-gradle-plugin/src/test/projects/signing/lib/build.gradle.kts
index 5daf4e37e8..aac836e4d8 100644
--- a/zipline-gradle-plugin/src/test/projects/signing/lib/build.gradle.kts
+++ b/zipline-gradle-plugin/src/test/projects/signing/lib/build.gradle.kts
@@ -8,7 +8,7 @@ plugins {
 }
 
 kotlin {
-  js() {
+  js {
     browser()
     binaries.executable()
   }
diff --git a/zipline/api/android/zipline.api b/zipline/api/android/zipline.api
index c0ef7ed019..e9dcdbaa44 100644
--- a/zipline/api/android/zipline.api
+++ b/zipline/api/android/zipline.api
@@ -198,23 +198,29 @@ public abstract interface class app/cash/zipline/ZiplineFunction {
 
 public final class app/cash/zipline/ZiplineManifest {
 	public static final field Companion Lapp/cash/zipline/ZiplineManifest$Companion;
-	public synthetic fun <init> (ILapp/cash/zipline/ZiplineManifest$Unsigned;Ljava/util/Map;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;Lkotlinx/serialization/internal/SerializationConstructorMarker;)V
-	public synthetic fun <init> (Lapp/cash/zipline/ZiplineManifest$Unsigned;Ljava/util/Map;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;Lkotlin/jvm/internal/DefaultConstructorMarker;)V
+	public synthetic fun <init> (ILapp/cash/zipline/ZiplineManifest$Unsigned;Ljava/util/Map;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;Ljava/util/Map;Lkotlinx/serialization/internal/SerializationConstructorMarker;)V
+	public synthetic fun <init> (Lapp/cash/zipline/ZiplineManifest$Unsigned;Ljava/util/Map;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;Ljava/util/Map;Lkotlin/jvm/internal/DefaultConstructorMarker;)V
 	public final fun component1 ()Lapp/cash/zipline/ZiplineManifest$Unsigned;
 	public final fun component2 ()Ljava/util/Map;
 	public final fun component3 ()Ljava/lang/String;
 	public final fun component4 ()Ljava/lang/String;
 	public final fun component5 ()Ljava/lang/String;
-	public final fun copy (Lapp/cash/zipline/ZiplineManifest$Unsigned;Ljava/util/Map;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;)Lapp/cash/zipline/ZiplineManifest;
-	public final fun copy (Ljava/util/Map;Ljava/lang/Long;Ljava/lang/String;Ljava/util/Map;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;)Lapp/cash/zipline/ZiplineManifest;
+	public final fun component6 ()Ljava/util/Map;
+	public final synthetic fun copy (Lapp/cash/zipline/ZiplineManifest$Unsigned;Ljava/util/Map;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;)Lapp/cash/zipline/ZiplineManifest;
+	public final fun copy (Lapp/cash/zipline/ZiplineManifest$Unsigned;Ljava/util/Map;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;Ljava/util/Map;)Lapp/cash/zipline/ZiplineManifest;
+	public final synthetic fun copy (Ljava/util/Map;Ljava/lang/Long;Ljava/lang/String;Ljava/util/Map;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;)Lapp/cash/zipline/ZiplineManifest;
+	public final fun copy (Ljava/util/Map;Ljava/lang/Long;Ljava/lang/String;Ljava/util/Map;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;Ljava/util/Map;)Lapp/cash/zipline/ZiplineManifest;
 	public static synthetic fun copy$default (Lapp/cash/zipline/ZiplineManifest;Lapp/cash/zipline/ZiplineManifest$Unsigned;Ljava/util/Map;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;ILjava/lang/Object;)Lapp/cash/zipline/ZiplineManifest;
+	public static synthetic fun copy$default (Lapp/cash/zipline/ZiplineManifest;Lapp/cash/zipline/ZiplineManifest$Unsigned;Ljava/util/Map;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;Ljava/util/Map;ILjava/lang/Object;)Lapp/cash/zipline/ZiplineManifest;
 	public static synthetic fun copy$default (Lapp/cash/zipline/ZiplineManifest;Ljava/util/Map;Ljava/lang/Long;Ljava/lang/String;Ljava/util/Map;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;ILjava/lang/Object;)Lapp/cash/zipline/ZiplineManifest;
+	public static synthetic fun copy$default (Lapp/cash/zipline/ZiplineManifest;Ljava/util/Map;Ljava/lang/Long;Ljava/lang/String;Ljava/util/Map;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;Ljava/util/Map;ILjava/lang/Object;)Lapp/cash/zipline/ZiplineManifest;
 	public final fun encodeJson ()Ljava/lang/String;
 	public fun equals (Ljava/lang/Object;)Z
 	public final fun getBaseUrl ()Ljava/lang/String;
 	public final fun getFreshAtEpochMs ()Ljava/lang/Long;
 	public final fun getMainFunction ()Ljava/lang/String;
 	public final fun getMainModuleId ()Ljava/lang/String;
+	public final fun getMetadata ()Ljava/util/Map;
 	public final fun getModules ()Ljava/util/Map;
 	public final fun getSignaturePayload ()Lokio/ByteString;
 	public final fun getSignatures ()Ljava/util/Map;
@@ -237,8 +243,10 @@ public final class app/cash/zipline/ZiplineManifest$$serializer : kotlinx/serial
 }
 
 public final class app/cash/zipline/ZiplineManifest$Companion {
-	public final fun create (Ljava/util/Map;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;Ljava/lang/Long;Ljava/lang/String;)Lapp/cash/zipline/ZiplineManifest;
+	public final synthetic fun create (Ljava/util/Map;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;Ljava/lang/Long;Ljava/lang/String;)Lapp/cash/zipline/ZiplineManifest;
+	public final fun create (Ljava/util/Map;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;Ljava/lang/Long;Ljava/lang/String;Ljava/util/Map;)Lapp/cash/zipline/ZiplineManifest;
 	public static synthetic fun create$default (Lapp/cash/zipline/ZiplineManifest$Companion;Ljava/util/Map;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;Ljava/lang/Long;Ljava/lang/String;ILjava/lang/Object;)Lapp/cash/zipline/ZiplineManifest;
+	public static synthetic fun create$default (Lapp/cash/zipline/ZiplineManifest$Companion;Ljava/util/Map;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;Ljava/lang/Long;Ljava/lang/String;Ljava/util/Map;ILjava/lang/Object;)Lapp/cash/zipline/ZiplineManifest;
 	public final fun decodeJson (Ljava/lang/String;)Lapp/cash/zipline/ZiplineManifest;
 	public final fun serializer ()Lkotlinx/serialization/KSerializer;
 }
diff --git a/zipline/api/jvm/zipline.api b/zipline/api/jvm/zipline.api
index c0ef7ed019..e9dcdbaa44 100644
--- a/zipline/api/jvm/zipline.api
+++ b/zipline/api/jvm/zipline.api
@@ -198,23 +198,29 @@ public abstract interface class app/cash/zipline/ZiplineFunction {
 
 public final class app/cash/zipline/ZiplineManifest {
 	public static final field Companion Lapp/cash/zipline/ZiplineManifest$Companion;
-	public synthetic fun <init> (ILapp/cash/zipline/ZiplineManifest$Unsigned;Ljava/util/Map;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;Lkotlinx/serialization/internal/SerializationConstructorMarker;)V
-	public synthetic fun <init> (Lapp/cash/zipline/ZiplineManifest$Unsigned;Ljava/util/Map;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;Lkotlin/jvm/internal/DefaultConstructorMarker;)V
+	public synthetic fun <init> (ILapp/cash/zipline/ZiplineManifest$Unsigned;Ljava/util/Map;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;Ljava/util/Map;Lkotlinx/serialization/internal/SerializationConstructorMarker;)V
+	public synthetic fun <init> (Lapp/cash/zipline/ZiplineManifest$Unsigned;Ljava/util/Map;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;Ljava/util/Map;Lkotlin/jvm/internal/DefaultConstructorMarker;)V
 	public final fun component1 ()Lapp/cash/zipline/ZiplineManifest$Unsigned;
 	public final fun component2 ()Ljava/util/Map;
 	public final fun component3 ()Ljava/lang/String;
 	public final fun component4 ()Ljava/lang/String;
 	public final fun component5 ()Ljava/lang/String;
-	public final fun copy (Lapp/cash/zipline/ZiplineManifest$Unsigned;Ljava/util/Map;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;)Lapp/cash/zipline/ZiplineManifest;
-	public final fun copy (Ljava/util/Map;Ljava/lang/Long;Ljava/lang/String;Ljava/util/Map;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;)Lapp/cash/zipline/ZiplineManifest;
+	public final fun component6 ()Ljava/util/Map;
+	public final synthetic fun copy (Lapp/cash/zipline/ZiplineManifest$Unsigned;Ljava/util/Map;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;)Lapp/cash/zipline/ZiplineManifest;
+	public final fun copy (Lapp/cash/zipline/ZiplineManifest$Unsigned;Ljava/util/Map;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;Ljava/util/Map;)Lapp/cash/zipline/ZiplineManifest;
+	public final synthetic fun copy (Ljava/util/Map;Ljava/lang/Long;Ljava/lang/String;Ljava/util/Map;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;)Lapp/cash/zipline/ZiplineManifest;
+	public final fun copy (Ljava/util/Map;Ljava/lang/Long;Ljava/lang/String;Ljava/util/Map;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;Ljava/util/Map;)Lapp/cash/zipline/ZiplineManifest;
 	public static synthetic fun copy$default (Lapp/cash/zipline/ZiplineManifest;Lapp/cash/zipline/ZiplineManifest$Unsigned;Ljava/util/Map;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;ILjava/lang/Object;)Lapp/cash/zipline/ZiplineManifest;
+	public static synthetic fun copy$default (Lapp/cash/zipline/ZiplineManifest;Lapp/cash/zipline/ZiplineManifest$Unsigned;Ljava/util/Map;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;Ljava/util/Map;ILjava/lang/Object;)Lapp/cash/zipline/ZiplineManifest;
 	public static synthetic fun copy$default (Lapp/cash/zipline/ZiplineManifest;Ljava/util/Map;Ljava/lang/Long;Ljava/lang/String;Ljava/util/Map;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;ILjava/lang/Object;)Lapp/cash/zipline/ZiplineManifest;
+	public static synthetic fun copy$default (Lapp/cash/zipline/ZiplineManifest;Ljava/util/Map;Ljava/lang/Long;Ljava/lang/String;Ljava/util/Map;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;Ljava/util/Map;ILjava/lang/Object;)Lapp/cash/zipline/ZiplineManifest;
 	public final fun encodeJson ()Ljava/lang/String;
 	public fun equals (Ljava/lang/Object;)Z
 	public final fun getBaseUrl ()Ljava/lang/String;
 	public final fun getFreshAtEpochMs ()Ljava/lang/Long;
 	public final fun getMainFunction ()Ljava/lang/String;
 	public final fun getMainModuleId ()Ljava/lang/String;
+	public final fun getMetadata ()Ljava/util/Map;
 	public final fun getModules ()Ljava/util/Map;
 	public final fun getSignaturePayload ()Lokio/ByteString;
 	public final fun getSignatures ()Ljava/util/Map;
@@ -237,8 +243,10 @@ public final class app/cash/zipline/ZiplineManifest$$serializer : kotlinx/serial
 }
 
 public final class app/cash/zipline/ZiplineManifest$Companion {
-	public final fun create (Ljava/util/Map;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;Ljava/lang/Long;Ljava/lang/String;)Lapp/cash/zipline/ZiplineManifest;
+	public final synthetic fun create (Ljava/util/Map;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;Ljava/lang/Long;Ljava/lang/String;)Lapp/cash/zipline/ZiplineManifest;
+	public final fun create (Ljava/util/Map;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;Ljava/lang/Long;Ljava/lang/String;Ljava/util/Map;)Lapp/cash/zipline/ZiplineManifest;
 	public static synthetic fun create$default (Lapp/cash/zipline/ZiplineManifest$Companion;Ljava/util/Map;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;Ljava/lang/Long;Ljava/lang/String;ILjava/lang/Object;)Lapp/cash/zipline/ZiplineManifest;
+	public static synthetic fun create$default (Lapp/cash/zipline/ZiplineManifest$Companion;Ljava/util/Map;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;Ljava/lang/Long;Ljava/lang/String;Ljava/util/Map;ILjava/lang/Object;)Lapp/cash/zipline/ZiplineManifest;
 	public final fun decodeJson (Ljava/lang/String;)Lapp/cash/zipline/ZiplineManifest;
 	public final fun serializer ()Lkotlinx/serialization/KSerializer;
 }
diff --git a/zipline/src/hostMain/kotlin/app/cash/zipline/ZiplineManifest.kt b/zipline/src/hostMain/kotlin/app/cash/zipline/ZiplineManifest.kt
index e725bcafc5..4e3a450f52 100644
--- a/zipline/src/hostMain/kotlin/app/cash/zipline/ZiplineManifest.kt
+++ b/zipline/src/hostMain/kotlin/app/cash/zipline/ZiplineManifest.kt
@@ -22,7 +22,6 @@ import app.cash.zipline.internal.jsonForManifest
 import app.cash.zipline.internal.signaturePayload
 import app.cash.zipline.internal.topologicalSort
 import kotlinx.serialization.Serializable
-import kotlinx.serialization.decodeFromString
 import kotlinx.serialization.encodeToString
 import okio.ByteString
 import okio.ByteString.Companion.encodeUtf8
@@ -51,6 +50,12 @@ data class ZiplineManifest private constructor(
 
   /** Version to represent the code as defined in this manifest, by default it will be Git commit SHA. */
   val version: String? = null,
+
+  /**
+   * Arbitrary application-layer metadata about this release. Use this to embed build or diagnostic
+   * metadata, such as the timestamp that this application was built.
+   */
+  val metadata: Map<String, String> = mapOf(),
 ) {
   init {
     require(modules.keys.toList().isTopologicallySorted { id -> modules[id]!!.dependsOnIds }) {
@@ -108,6 +113,50 @@ data class ZiplineManifest private constructor(
   val baseUrl: String?
     get() = unsigned.baseUrl
 
+  @Deprecated(
+    message = "This is here for binary-compatibility only",
+    level = DeprecationLevel.HIDDEN,
+  )
+  fun copy(
+    signatures: Map<String, String> = this.signatures,
+    freshAtEpochMs: Long? = this.freshAtEpochMs,
+    baseUrl: String? = this.baseUrl,
+    modules: Map<String, Module> = this.modules,
+    mainModuleId: String = this.mainModuleId,
+    mainFunction: String? = this.mainFunction,
+    version: String? = this.version,
+  ): ZiplineManifest = copy(
+    unsigned = unsigned.copy(
+      freshAtEpochMs = freshAtEpochMs,
+      signatures = signatures,
+      baseUrl = baseUrl,
+    ),
+    modules = modules,
+    mainModuleId = mainModuleId,
+    mainFunction = mainFunction,
+    version = version,
+    metadata = this.metadata,
+  )
+
+  @Deprecated(
+    message = "This is here for binary-compatibility only",
+    level = DeprecationLevel.HIDDEN,
+  )
+  fun copy(
+    unsigned: Unsigned = this.unsigned,
+    modules: Map<String, Module> = this.modules,
+    mainModuleId: String = this.mainModuleId,
+    mainFunction: String? = this.mainFunction,
+    version: String? = this.version,
+  ): ZiplineManifest = copy(
+    unsigned = unsigned,
+    modules = modules,
+    mainModuleId = mainModuleId,
+    mainFunction = mainFunction,
+    version = version,
+    metadata = this.metadata,
+  )
+
   fun copy(
     signatures: Map<String, String> = this.signatures,
     freshAtEpochMs: Long? = this.freshAtEpochMs,
@@ -116,7 +165,8 @@ data class ZiplineManifest private constructor(
     mainModuleId: String = this.mainModuleId,
     mainFunction: String? = this.mainFunction,
     version: String? = this.version,
-  ) = copy(
+    metadata: Map<String, String> = this.metadata,
+  ): ZiplineManifest = copy(
     unsigned = unsigned.copy(
       freshAtEpochMs = freshAtEpochMs,
       signatures = signatures,
@@ -126,6 +176,8 @@ data class ZiplineManifest private constructor(
     mainModuleId = mainModuleId,
     mainFunction = mainFunction,
     version = version,
+    // Defensive copy!
+    metadata = metadata.toMap(),
   )
 
   /**
@@ -151,6 +203,29 @@ data class ZiplineManifest private constructor(
   }
 
   companion object {
+    @Deprecated(
+      message = "This is here for binary-compatibility only",
+      level = DeprecationLevel.HIDDEN,
+    )
+    fun create(
+      modules: Map<String, Module>,
+      mainFunction: String? = null,
+      mainModuleId: String? = null,
+      version: String? = null,
+      builtAtEpochMs: Long? = null,
+      baseUrl: String? = null,
+    ): ZiplineManifest {
+      return create(
+        modules = modules,
+        mainFunction = mainFunction,
+        mainModuleId = mainModuleId,
+        version = version,
+        builtAtEpochMs = builtAtEpochMs,
+        baseUrl = baseUrl,
+        metadata = mapOf(),
+      )
+    }
+
     fun create(
       modules: Map<String, Module>,
       mainFunction: String? = null,
@@ -158,6 +233,7 @@ data class ZiplineManifest private constructor(
       version: String? = null,
       builtAtEpochMs: Long? = null,
       baseUrl: String? = null,
+      metadata: Map<String, String> = mapOf(),
     ): ZiplineManifest {
       val sortedModuleIds = modules.keys
         .toList()
@@ -178,6 +254,8 @@ data class ZiplineManifest private constructor(
         mainModuleId = mainModuleId ?: sortedModuleIds.last(),
         mainFunction = mainFunction,
         version = version,
+        // Defensive copy!
+        metadata = metadata.toMap(),
       )
     }
 
diff --git a/zipline/src/hostTest/kotlin/app/cash/zipline/ZiplineManifestTest.kt b/zipline/src/hostTest/kotlin/app/cash/zipline/ZiplineManifestTest.kt
index f5cb76e35c..0943660855 100644
--- a/zipline/src/hostTest/kotlin/app/cash/zipline/ZiplineManifestTest.kt
+++ b/zipline/src/hostTest/kotlin/app/cash/zipline/ZiplineManifestTest.kt
@@ -19,6 +19,8 @@ package app.cash.zipline
 import kotlin.test.Test
 import kotlin.test.assertEquals
 import kotlin.test.assertFailsWith
+import kotlin.test.assertNotSame
+import kotlin.test.assertSame
 import okio.ByteString.Companion.encodeUtf8
 
 class ZiplineManifestTest {
@@ -168,6 +170,7 @@ class ZiplineManifestTest {
         ),
       ),
       mainFunction = "zipline.ziplineMain",
+      metadata = mapOf("build_timestamp" to "2023-10-25T12:00:00T"),
     )
 
     val serialized = original.encodeJson()
@@ -197,7 +200,10 @@ class ZiplineManifestTest {
         |  },
         |  "mainModuleId": "bravo",
         |  "mainFunction": "zipline.ziplineMain",
-        |  "version": null
+        |  "version": null,
+        |  "metadata": {
+        |    "build_timestamp": "2023-10-25T12:00:00T"
+        |  }
         |}
         """.trimMargin(),
       prettyPrint(serialized),
@@ -270,4 +276,50 @@ class ZiplineManifestTest {
       ZiplineManifest.decodeJson(serialized),
     )
   }
+
+  /**
+   * Confirm we attempt to make defensive copies. Note that this isn't perfect and we observe
+   * mutable instances with [copy].
+   */
+  @Test
+  fun metadataIsDefensivelyCopiedByCreate() {
+    val mutableMetadata = mutableMapOf<String, String>()
+    val manifest = ZiplineManifest.create(
+      modules = mapOf(
+        "alpha" to ZiplineManifest.Module(
+          url = "/alpha.zipline",
+          sha256 = "abc123".encodeUtf8(),
+          dependsOnIds = listOf(),
+        ),
+      ),
+      mainFunction = "zipline.ziplineMain",
+      metadata = mutableMetadata,
+    )
+
+    assertNotSame(mutableMetadata, manifest.metadata)
+
+    mutableMetadata["build_timestamp"] = "2023-10-25T12:00:00T"
+    assertEquals(mapOf(), manifest.metadata)
+  }
+
+  @Test
+  fun metadataIsNotDefensivelyCopiedByDataClassCopy() {
+    val mutableMetadata = mutableMapOf<String, String>()
+    val manifest = ZiplineManifest.create(
+      modules = mapOf(
+        "alpha" to ZiplineManifest.Module(
+          url = "/alpha.zipline",
+          sha256 = "abc123".encodeUtf8(),
+          dependsOnIds = listOf(),
+        ),
+      ),
+      mainFunction = "zipline.ziplineMain",
+    ).copy(
+      metadata = mutableMetadata,
+    )
+
+    // This isn't the behavior we want, but it's the behavior we get. There's no good way to do
+    // defensive copies with data classes, and ZiplineManifest should have used POKO. Sigh.
+    assertSame(mutableMetadata, manifest.metadata)
+  }
 }
diff --git a/zipline/src/hostTest/kotlin/app/cash/zipline/internal/SignaturePayloadTest.kt b/zipline/src/hostTest/kotlin/app/cash/zipline/internal/SignaturePayloadTest.kt
index 21a86d18bc..39e267c5f2 100644
--- a/zipline/src/hostTest/kotlin/app/cash/zipline/internal/SignaturePayloadTest.kt
+++ b/zipline/src/hostTest/kotlin/app/cash/zipline/internal/SignaturePayloadTest.kt
@@ -172,6 +172,29 @@ class SignaturePayloadTest {
     )
   }
 
+  @Test
+  fun metadataIsSignificant() {
+    val manifestA = ZiplineManifest.create(
+      modules = mapOf(
+        "./kotlin_kotlin.js" to ZiplineManifest.Module(
+          url = "kotlin_kotlin.zipline",
+          sha256 = "6bd4baa9f46afa62477fec8c9e95528de7539f036d26fc13885177b32fc0d6ab".decodeHex(),
+          dependsOnIds = listOf(),
+        ),
+      ),
+      metadata = mapOf("build_timestamp" to "2023-10-25T12:00:00T"),
+    )
+
+    val manifestB = manifestA.copy(
+      metadata = mapOf(),
+    )
+
+    assertNotEquals(
+      manifestA.signaturePayload,
+      manifestB.signaturePayload,
+    )
+  }
+
   @Test
   fun signaturePayloadStripsBaseUrlsAndSignatures() {
     val manifestJson = """