diff --git a/core/src/main/java/com/google/adk/events/EventActions.java b/core/src/main/java/com/google/adk/events/EventActions.java
index bf25acfc7..b9092e86e 100644
--- a/core/src/main/java/com/google/adk/events/EventActions.java
+++ b/core/src/main/java/com/google/adk/events/EventActions.java
@@ -110,12 +110,16 @@ public void removeStateByKey(String key) {
   }
 
   @JsonProperty("artifactDelta")
-  public ConcurrentMap<String, Integer> artifactDelta() {
+  public Map<String, Integer> artifactDelta() {
     return artifactDelta;
   }
 
-  public void setArtifactDelta(ConcurrentMap<String, Integer> artifactDelta) {
-    this.artifactDelta = artifactDelta;
+  public void setArtifactDelta(Map<String, Integer> artifactDelta) {
+    if (artifactDelta instanceof ConcurrentMap) {
+      this.artifactDelta = (ConcurrentMap<String, Integer>) artifactDelta;
+    } else {
+      this.artifactDelta = new ConcurrentHashMap<>(artifactDelta);
+    }
   }
 
   @JsonProperty("deletedArtifactIds")
diff --git a/core/src/test/java/com/google/adk/events/EventActionsTest.java b/core/src/test/java/com/google/adk/events/EventActionsTest.java
index 28123bab8..8577b7873 100644
--- a/core/src/test/java/com/google/adk/events/EventActionsTest.java
+++ b/core/src/test/java/com/google/adk/events/EventActionsTest.java
@@ -26,6 +26,7 @@
 import com.google.genai.types.Part;
 import java.util.Map;
 import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ConcurrentMap;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.junit.runners.JUnit4;
@@ -109,6 +110,29 @@ public void merge_mergesAllFields() {
     assertThat(merged.compaction()).hasValue(COMPACTION);
   }
 
+  @Test
+  public void setArtifactDelta_reusesConcurrentMap() {
+    EventActions eventActions = new EventActions();
+    ConcurrentMap<String, Integer> artifactDelta = new ConcurrentHashMap<>();
+    artifactDelta.put("artifact1", 1);
+
+    eventActions.setArtifactDelta(artifactDelta);
+
+    assertThat(eventActions.artifactDelta()).isSameInstanceAs(artifactDelta);
+  }
+
+  @Test
+  public void setArtifactDelta_copiesRegularMap() {
+    EventActions eventActions = new EventActions();
+    ImmutableMap<String, Integer> artifactDelta = ImmutableMap.of("artifact1", 1);
+
+    eventActions.setArtifactDelta(artifactDelta);
+
+    assertThat(eventActions.artifactDelta()).isNotSameInstanceAs(artifactDelta);
+    assertThat(eventActions.artifactDelta()).containsExactly("artifact1", 1);
+    assertThat(eventActions.artifactDelta()).isInstanceOf(ConcurrentMap.class);
+  }
+
   @Test
   public void removeStateByKey_marksKeyAsRemoved() {
     EventActions eventActions = new EventActions();