diff --git a/pom.xml b/pom.xml
index afb900088..66ce647fa 100644
--- a/pom.xml
+++ b/pom.xml
@@ -75,7 +75,7 @@
     <kotlin.version>2.3.21</kotlin.version>
     <dokka.version>2.2.0</dokka.version>
     <kotlinx-coroutines.version>1.11.0</kotlinx-coroutines.version>
-    <adk-kotlin.version>1.4.0</adk-kotlin.version>
+    <adk-kotlin.version>1.5.0</adk-kotlin.version>
     <reactor-core.version>3.7.0</reactor-core.version>
     <wiremock.version>2.35.1</wiremock.version>
     <assertj.version>3.27.7</assertj.version>
diff --git a/tokt/src/main/kotlin/com/google/adk/tokt/JavaAdkToKt.kt b/tokt/src/main/kotlin/com/google/adk/tokt/JavaAdkToKt.kt
index 24af4a6ab..7628b46cd 100644
--- a/tokt/src/main/kotlin/com/google/adk/tokt/JavaAdkToKt.kt
+++ b/tokt/src/main/kotlin/com/google/adk/tokt/JavaAdkToKt.kt
@@ -141,7 +141,8 @@ object JavaAdkToKt {
    * Java view of a Kotlin service is unwrapped to that Kotlin service, with no `dispatcher` hop.
    * Resumption and rewinds work across the adapter if the Java service, like
    * `InMemorySessionService`, returns the fields they read unchanged: `EventActions.agentState`,
-   * `rewindBeforeInvocationId`, and a workflow node's output, node info, and routes.
+   * `rewindBeforeInvocationId`, `Event.isolationScope`, and a workflow node's output, node info,
+   * and routes.
    */
   @JvmStatic
   @JvmOverloads
diff --git a/tokt/src/main/kotlin/com/google/adk/tokt/codecs/EventCodec.kt b/tokt/src/main/kotlin/com/google/adk/tokt/codecs/EventCodec.kt
index 59fc574cb..efb57146f 100644
--- a/tokt/src/main/kotlin/com/google/adk/tokt/codecs/EventCodec.kt
+++ b/tokt/src/main/kotlin/com/google/adk/tokt/codecs/EventCodec.kt
@@ -36,7 +36,7 @@ import kotlin.jvm.optionals.getOrNull
  * `errorCode`, `finishReason`), the token `usageMetadata` ([UsageMetadataCodec]),
  * `groundingMetadata` ([GroundingMetadataCodec]) and context `cacheMetadata`
  * ([CacheMetadataCodec]), a workflow node's `output` and `nodeInfo` ([WorkflowCodec]), long-running
- * tool ids, and the timestamp.
+ * tool ids, the timestamp, and the `isolationScope`.
  */
 internal object EventCodec {
 
@@ -49,6 +49,7 @@ internal object EventCodec {
         .actions(eventActionsToJava(event.actions))
     event.invocationId?.let { builder.invocationId(it) }
     event.branch?.let { builder.branch(it) }
+    event.isolationScope?.let { builder.isolationScope(it) }
     event.content?.let { builder.content(ContentCodec.toJava(it)) }
     if (event.longRunningToolIds.isNotEmpty()) builder.longRunningToolIds(event.longRunningToolIds)
     // Streaming/error signals are set only when meaningful, so ordinary events keep the Java
@@ -101,6 +102,7 @@ internal object EventCodec {
           route = javaActions.route().getOrNull()?.map { WorkflowCodec.routeFromJava(it) },
         ),
       branch = event.branch().getOrNull(),
+      isolationScope = event.isolationScope().getOrNull(),
       partial = event.partial().getOrNull() ?: false,
       turnComplete = event.turnComplete().getOrNull() ?: false,
       interrupted = event.interrupted().getOrNull() ?: false,
diff --git a/tokt/src/test/kotlin/com/google/adk/tokt/KtRunnerInteropTest.kt b/tokt/src/test/kotlin/com/google/adk/tokt/KtRunnerInteropTest.kt
index d47b1f9a8..a9aec4db6 100644
--- a/tokt/src/test/kotlin/com/google/adk/tokt/KtRunnerInteropTest.kt
+++ b/tokt/src/test/kotlin/com/google/adk/tokt/KtRunnerInteropTest.kt
@@ -4383,6 +4383,21 @@ class KtRunnerInteropTest {
     assertEquals(listOf(fingerprintOnly, active), stored)
   }
 
+  @Test
+  fun asKtSessionService_isolationScope_survivesTheJavaStore() = runBlocking {
+    // A task agent resumes from events in its own scope, so the scope must survive storage.
+    val sessions = JavaAdkToKt.asKtSessionService(JavaInMemorySessionService())
+    val key = KtSessionKey("app", "u", "s")
+    val session = sessions.createSession(key)
+
+    val unusedScoped =
+      sessions.appendEvent(session, KtEvent(author = "task", isolationScope = "task-1"))
+    val unusedUnscoped = sessions.appendEvent(session, KtEvent(author = "user"))
+
+    val stored = assertNotNull(sessions.getSession(key)).events.map { it.isolationScope }
+    assertEquals(listOf("task-1", null), stored)
+  }
+
   @Test
   fun eventCodec_workflowFields_roundTripThroughTheJavaEvent() {
     // Java code reads these fields too, so a Kotlin Content in the output crosses as a genai one.