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 cde23c10e..063a56a44 100644
--- a/core/src/main/java/com/google/adk/events/EventActions.java
+++ b/core/src/main/java/com/google/adk/events/EventActions.java
@@ -21,6 +21,7 @@
 import com.google.adk.JsonBaseModel;
 import com.google.adk.sessions.State;
 import com.google.errorprone.annotations.CanIgnoreReturnValue;
+import java.util.HashMap;
 import java.util.HashSet;
 import java.util.Map;
 import java.util.Objects;
@@ -44,6 +45,7 @@ public class EventActions extends JsonBaseModel {
   private ConcurrentMap<String, Map<String, Object>> requestedAuthConfigs;
   private ConcurrentMap<String, ToolConfirmation> requestedToolConfirmations;
   private boolean endOfAgent;
+  private @Nullable Map<String, Object> agentState;
   private @Nullable EventCompaction compaction;
 
   /** Default constructor for Jackson. */
@@ -66,6 +68,7 @@ private EventActions(Builder builder) {
     this.requestedAuthConfigs = builder.requestedAuthConfigs;
     this.requestedToolConfirmations = builder.requestedToolConfirmations;
     this.endOfAgent = builder.endOfAgent;
+    this.agentState = builder.agentState;
     this.compaction = builder.compaction;
   }
 
@@ -192,6 +195,19 @@ public void setEndInvocation(boolean endInvocation) {
     this.endOfAgent = endInvocation;
   }
 
+  /**
+   * The checkpointed state of the authoring agent at this event, used for session resumability.
+   * Only set by ADK workflow/agent machinery on resumable invocations.
+   */
+  @JsonProperty("agentState")
+  public Optional<Map<String, Object>> agentState() {
+    return Optional.ofNullable(agentState);
+  }
+
+  public void setAgentState(@Nullable Map<String, Object> agentState) {
+    this.agentState = agentState;
+  }
+
   @JsonProperty("compaction")
   public Optional<EventCompaction> compaction() {
     return Optional.ofNullable(compaction);
@@ -226,6 +242,7 @@ public boolean equals(Object o) {
         && Objects.equals(requestedAuthConfigs, that.requestedAuthConfigs)
         && Objects.equals(requestedToolConfirmations, that.requestedToolConfirmations)
         && (endOfAgent == that.endOfAgent)
+        && Objects.equals(agentState, that.agentState)
         && Objects.equals(compaction, that.compaction);
   }
 
@@ -241,6 +258,7 @@ public int hashCode() {
         requestedAuthConfigs,
         requestedToolConfirmations,
         endOfAgent,
+        agentState,
         compaction);
   }
 
@@ -255,6 +273,7 @@ public static class Builder {
     private ConcurrentMap<String, Map<String, Object>> requestedAuthConfigs;
     private ConcurrentMap<String, ToolConfirmation> requestedToolConfirmations;
     private boolean endOfAgent = false;
+    private @Nullable Map<String, Object> agentState;
     private @Nullable EventCompaction compaction;
 
     public Builder() {
@@ -276,6 +295,8 @@ private Builder(EventActions eventActions) {
       this.requestedToolConfirmations =
           new ConcurrentHashMap<>(eventActions.requestedToolConfirmations());
       this.endOfAgent = eventActions.endOfAgent;
+      this.agentState =
+          eventActions.agentState == null ? null : new HashMap<>(eventActions.agentState);
       this.compaction = eventActions.compaction;
     }
 
@@ -376,6 +397,13 @@ public Builder endInvocation(boolean endInvocation) {
       return this;
     }
 
+    @CanIgnoreReturnValue
+    @JsonProperty("agentState")
+    public Builder agentState(@Nullable Map<String, Object> agentState) {
+      this.agentState = agentState;
+      return this;
+    }
+
     @CanIgnoreReturnValue
     @JsonProperty("compaction")
     public Builder compaction(@Nullable EventCompaction value) {
@@ -394,6 +422,7 @@ public Builder merge(EventActions other) {
       this.requestedAuthConfigs.putAll(other.requestedAuthConfigs());
       this.requestedToolConfirmations.putAll(other.requestedToolConfirmations());
       this.endOfAgent = this.endOfAgent || other.endOfAgent();
+      other.agentState().ifPresent(this::agentState);
       other.compaction().ifPresent(this::compaction);
       return this;
     }
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 c5949caf7..77fb805d4 100644
--- a/core/src/test/java/com/google/adk/events/EventActionsTest.java
+++ b/core/src/test/java/com/google/adk/events/EventActionsTest.java
@@ -111,6 +111,61 @@ public void merge_mergesAllFields() {
     assertThat(merged.compaction()).hasValue(COMPACTION);
   }
 
+  @Test
+  public void agentState_roundTripsThroughToBuilder() {
+    EventActions actions =
+        EventActions.builder().agentState(ImmutableMap.of("current_sub_agent", "b")).build();
+
+    EventActions rebuilt = actions.toBuilder().build();
+
+    assertThat(rebuilt).isEqualTo(actions);
+    assertThat(rebuilt.agentState()).hasValue(ImmutableMap.of("current_sub_agent", "b"));
+  }
+
+  @Test
+  public void agentState_roundTripsThroughJson() {
+    EventActions actions =
+        EventActions.builder().agentState(ImmutableMap.of("times_looped", 2)).build();
+
+    EventActions deserialized = EventActions.fromJsonString(actions.toJson(), EventActions.class);
+
+    assertThat(deserialized.agentState()).isPresent();
+    assertThat(deserialized.agentState().get()).containsEntry("times_looped", 2);
+  }
+
+  @Test
+  public void agentState_absentByDefault_andOmittedFromJson() {
+    EventActions actions = EventActions.builder().build();
+
+    assertThat(actions.agentState()).isEmpty();
+    // Kept out of the serialized form so pre-existing events stay byte-identical.
+    assertThat(actions.toJson()).doesNotContain("agentState");
+  }
+
+  @Test
+  public void merge_agentState_lastWins() {
+    EventActions first =
+        EventActions.builder().agentState(ImmutableMap.of("current_sub_agent", "a")).build();
+    EventActions second =
+        EventActions.builder().agentState(ImmutableMap.of("current_sub_agent", "b")).build();
+
+    EventActions merged = first.toBuilder().merge(second).build();
+
+    assertThat(merged.agentState()).hasValue(ImmutableMap.of("current_sub_agent", "b"));
+  }
+
+  @Test
+  public void merge_agentState_disjointKeys_replacesWholeMap() {
+    // agentState is a single checkpoint payload: merge replaces it wholesale (last-wins) rather
+    // than deep-merging keys.
+    EventActions first = EventActions.builder().agentState(ImmutableMap.of("a", 1)).build();
+    EventActions second = EventActions.builder().agentState(ImmutableMap.of("b", 2)).build();
+
+    EventActions merged = first.toBuilder().merge(second).build();
+
+    assertThat(merged.agentState()).hasValue(ImmutableMap.of("b", 2));
+  }
+
   @Test
   public void merge_endOfAgentIsOrderIndependent() {
     // A tool that ends the invocation, and one that leaves the flag at its default false. Folding