google · copybara-service · Jan 27, 2026 · Jan 27, 2026
diff --git a/core/src/main/java/com/google/adk/agents/BaseAgentState.java b/core/src/main/java/com/google/adk/agents/BaseAgentState.java
@@ -0,0 +1,39 @@
+/*
+ * Copyright 2026 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.adk.agents;
+
+import com.google.adk.JsonBaseModel;
+
+/** Base class for all agent states. */
+public class BaseAgentState extends JsonBaseModel {
+
+  protected BaseAgentState() {}
+
+  /** Returns a new {@link Builder} for creating {@link BaseAgentState} instances. */
+  public static Builder builder() {
+    return new Builder();
+  }
+
+  /** Builder for {@link BaseAgentState}. */
+  public static class Builder {
+    private Builder() {}
+
+    public BaseAgentState build() {
+      return new BaseAgentState();
+    }
+  }
+}
diff --git a/core/src/main/java/com/google/adk/agents/InvocationContext.java b/core/src/main/java/com/google/adk/agents/InvocationContext.java
@@ -50,6 +50,8 @@ public class InvocationContext {
   private final Session session;
   private final Optional<Content> userContent;
   private final RunConfig runConfig;
+  private final Map<String, BaseAgentState> agentStates;
+  private final Map<String, Boolean> endOfAgents;
   private final ResumabilityConfig resumabilityConfig;
   private final InvocationCostManager invocationCostManager;
 
@@ -71,6 +73,8 @@ protected InvocationContext(Builder builder) {
     this.userContent = builder.userContent;
     this.runConfig = builder.runConfig;
     this.endInvocation = builder.endInvocation;
+    this.agentStates = builder.agentStates;
+    this.endOfAgents = builder.endOfAgents;
     this.resumabilityConfig = builder.resumabilityConfig;
     this.invocationCostManager = builder.invocationCostManager;
   }
@@ -299,6 +303,16 @@ public RunConfig runConfig() {
     return runConfig;
   }
 
+  /** Returns agent-specific state saved within this invocation. */
+  public Map<String, BaseAgentState> agentStates() {
+    return agentStates;
+  }
+
+  /** Returns map of agents that ended during this invocation. */
+  public Map<String, Boolean> endOfAgents() {
+    return endOfAgents;
+  }
+
   /**
    * Returns whether this invocation should be ended, e.g., due to reaching a terminal state or
    * error.
@@ -410,6 +424,8 @@ private Builder(InvocationContext context) {
       this.userContent = context.userContent;
       this.runConfig = context.runConfig;
       this.endInvocation = context.endInvocation;
+      this.agentStates = new ConcurrentHashMap<>(context.agentStates);
+      this.endOfAgents = new ConcurrentHashMap<>(context.endOfAgents);
       this.resumabilityConfig = context.resumabilityConfig;
       this.invocationCostManager = context.invocationCostManager;
     }
@@ -427,6 +443,8 @@ private Builder(InvocationContext context) {
     private Optional<Content> userContent = Optional.empty();
     private RunConfig runConfig = RunConfig.builder().build();
     private boolean endInvocation = false;
+    private Map<String, BaseAgentState> agentStates = new ConcurrentHashMap<>();
+    private Map<String, Boolean> endOfAgents = new ConcurrentHashMap<>();
     private ResumabilityConfig resumabilityConfig = new ResumabilityConfig();
     private InvocationCostManager invocationCostManager = new InvocationCostManager();
 
@@ -616,6 +634,30 @@ public Builder endInvocation(boolean endInvocation) {
       return this;
     }
 
+    /**
+     * Sets agent-specific state saved within this invocation.
+     *
+     * @param agentStates agent-specific state saved within this invocation.
+     * @return this builder instance for chaining.
+     */
+    @CanIgnoreReturnValue
+    public Builder agentStates(Map<String, BaseAgentState> agentStates) {
+      this.agentStates = agentStates;
+      return this;
+    }
+
+    /**
+     * Sets agent end-of-invocation status.
+     *
+     * @param endOfAgents agent end-of-invocation status.
+     * @return this builder instance for chaining.
+     */
+    @CanIgnoreReturnValue
+    public Builder endOfAgents(Map<String, Boolean> endOfAgents) {
+      this.endOfAgents = endOfAgents;
+      return this;
+    }
+
     /**
      * Sets the resumability configuration for the current agent run.
      *
@@ -660,6 +702,8 @@ public boolean equals(Object o) {
         && Objects.equals(session, that.session)
         && Objects.equals(userContent, that.userContent)
         && Objects.equals(runConfig, that.runConfig)
+        && Objects.equals(agentStates, that.agentStates)
+        && Objects.equals(endOfAgents, that.endOfAgents)
         && Objects.equals(resumabilityConfig, that.resumabilityConfig)
         && Objects.equals(invocationCostManager, that.invocationCostManager);
   }
@@ -680,6 +724,8 @@ public int hashCode() {
         userContent,
         runConfig,
         endInvocation,
+        agentStates,
+        endOfAgents,
         resumabilityConfig,
         invocationCostManager);
   }

diff --git a/core/src/main/java/com/google/adk/agents/LlmAgent.java b/core/src/main/java/com/google/adk/agents/LlmAgent.java
@@ -17,7 +17,6 @@
 package com.google.adk.agents;
 
 import static com.google.common.collect.ImmutableList.toImmutableList;
-import static java.util.Objects.requireNonNullElse;
 import static java.util.stream.Collectors.joining;
 
 import com.fasterxml.jackson.core.JsonProcessingException;
@@ -104,12 +103,12 @@ public enum IncludeContents {
   private final Optional<Integer> maxSteps;
   private final boolean disallowTransferToParent;
   private final boolean disallowTransferToPeers;
-  private final ImmutableList<? extends BeforeModelCallback> beforeModelCallback;
-  private final ImmutableList<? extends AfterModelCallback> afterModelCallback;
-  private final ImmutableList<? extends OnModelErrorCallback> onModelErrorCallback;
-  private final ImmutableList<? extends BeforeToolCallback> beforeToolCallback;
-  private final ImmutableList<? extends AfterToolCallback> afterToolCallback;
-  private final ImmutableList<? extends OnToolErrorCallback> onToolErrorCallback;
+  private final Optional<List<? extends BeforeModelCallback>> beforeModelCallback;
+  private final Optional<List<? extends AfterModelCallback>> afterModelCallback;
+  private final Optional<List<? extends OnModelErrorCallback>> onModelErrorCallback;
+  private final Optional<List<? extends BeforeToolCallback>> beforeToolCallback;
+  private final Optional<List<? extends AfterToolCallback>> afterToolCallback;
+  private final Optional<List<? extends OnToolErrorCallback>> onToolErrorCallback;
   private final Optional<Schema> inputSchema;
   private final Optional<Schema> outputSchema;
   private final Optional<Executor> executor;
@@ -127,28 +126,29 @@ protected LlmAgent(Builder builder) {
         builder.beforeAgentCallback,
         builder.afterAgentCallback);
     this.model = Optional.ofNullable(builder.model);
-    this.instruction = requireNonNullElse(builder.instruction, new Instruction.Static(""));
+    this.instruction =
+        builder.instruction == null ? new Instruction.Static("") : builder.instruction;
     this.globalInstruction =
-        requireNonNullElse(builder.globalInstruction, new Instruction.Static(""));
+        builder.globalInstruction == null ? new Instruction.Static("") : builder.globalInstruction;
     this.generateContentConfig = Optional.ofNullable(builder.generateContentConfig);
     this.exampleProvider = Optional.ofNullable(builder.exampleProvider);
-    this.includeContents = requireNonNullElse(builder.includeContents, IncludeContents.DEFAULT);
+    this.includeContents =
+        builder.includeContents != null ? builder.includeContents : IncludeContents.DEFAULT;
     this.planning = builder.planning != null && builder.planning;
     this.maxSteps = Optional.ofNullable(builder.maxSteps);
     this.disallowTransferToParent = builder.disallowTransferToParent;
     this.disallowTransferToPeers = builder.disallowTransferToPeers;
-    this.beforeModelCallback = requireNonNullElse(builder.beforeModelCallback, ImmutableList.of());
-    this.afterModelCallback = requireNonNullElse(builder.afterModelCallback, ImmutableList.of());
-    this.onModelErrorCallback =
-        requireNonNullElse(builder.onModelErrorCallback, ImmutableList.of());
-    this.beforeToolCallback = requireNonNullElse(builder.beforeToolCallback, ImmutableList.of());
-    this.afterToolCallback = requireNonNullElse(builder.afterToolCallback, ImmutableList.of());
-    this.onToolErrorCallback = requireNonNullElse(builder.onToolErrorCallback, ImmutableList.of());
+    this.beforeModelCallback = Optional.ofNullable(builder.beforeModelCallback);
+    this.afterModelCallback = Optional.ofNullable(builder.afterModelCallback);
+    this.onModelErrorCallback = Optional.ofNullable(builder.onModelErrorCallback);
+    this.beforeToolCallback = Optional.ofNullable(builder.beforeToolCallback);
+    this.afterToolCallback = Optional.ofNullable(builder.afterToolCallback);
+    this.onToolErrorCallback = Optional.ofNullable(builder.onToolErrorCallback);
     this.inputSchema = Optional.ofNullable(builder.inputSchema);
     this.outputSchema = Optional.ofNullable(builder.outputSchema);
     this.executor = Optional.ofNullable(builder.executor);
     this.outputKey = Optional.ofNullable(builder.outputKey);
-    this.toolsUnion = requireNonNullElse(builder.toolsUnion, ImmutableList.of());
+    this.toolsUnion = builder.toolsUnion != null ? builder.toolsUnion : ImmutableList.of();
     this.toolsets = extractToolsets(this.toolsUnion);
     this.codeExecutor = Optional.ofNullable(builder.codeExecutor);
 
@@ -704,16 +704,7 @@ private static boolean isThought(Part part) {
 
   @Override
   protected Flowable<Event> runAsyncImpl(InvocationContext invocationContext) {
-    return llmFlow
-        .run(invocationContext)
-        .concatMap(
-            event -> {
-              this.maybeSaveOutputToState(event);
-              if (invocationContext.shouldPauseInvocation(event)) {
-                return Flowable.just(event).concatWith(Flowable.empty());
-              }
-              return Flowable.just(event);
-            });
+    return llmFlow.run(invocationContext).doOnNext(this::maybeSaveOutputToState);
   }
 
   @Override
@@ -850,27 +841,27 @@ public boolean disallowTransferToPeers() {
     return disallowTransferToPeers;
   }
 
-  public List<? extends BeforeModelCallback> beforeModelCallback() {
+  public Optional<List<? extends BeforeModelCallback>> beforeModelCallback() {
     return beforeModelCallback;
   }
 
-  public List<? extends AfterModelCallback> afterModelCallback() {
+  public Optional<List<? extends AfterModelCallback>> afterModelCallback() {
     return afterModelCallback;
   }
 
-  public List<? extends BeforeToolCallback> beforeToolCallback() {
+  public Optional<List<? extends BeforeToolCallback>> beforeToolCallback() {
     return beforeToolCallback;
   }
 
-  public List<? extends AfterToolCallback> afterToolCallback() {
+  public Optional<List<? extends AfterToolCallback>> afterToolCallback() {
     return afterToolCallback;
   }
 
-  public List<? extends OnModelErrorCallback> onModelErrorCallback() {
+  public Optional<List<? extends OnModelErrorCallback>> onModelErrorCallback() {
     return onModelErrorCallback;
   }
 
-  public List<? extends OnToolErrorCallback> onToolErrorCallback() {
+  public Optional<List<? extends OnToolErrorCallback>> onToolErrorCallback() {
     return onToolErrorCallback;
   }
 
@@ -880,7 +871,7 @@ public List<? extends OnToolErrorCallback> onToolErrorCallback() {
    * <p>This method is only for use by Agent Development Kit.
    */
   public List<? extends BeforeModelCallback> canonicalBeforeModelCallbacks() {
-    return beforeModelCallback;
+    return beforeModelCallback.orElse(ImmutableList.of());
   }
 
   /**
@@ -889,7 +880,7 @@ public List<? extends BeforeModelCallback> canonicalBeforeModelCallbacks() {
    * <p>This method is only for use by Agent Development Kit.
    */
   public List<? extends AfterModelCallback> canonicalAfterModelCallbacks() {
-    return afterModelCallback;
+    return afterModelCallback.orElse(ImmutableList.of());
   }
 
   /**
@@ -898,7 +889,7 @@ public List<? extends AfterModelCallback> canonicalAfterModelCallbacks() {
    * <p>This method is only for use by Agent Development Kit.
    */
   public List<? extends OnModelErrorCallback> canonicalOnModelErrorCallbacks() {
-    return onModelErrorCallback;
+    return onModelErrorCallback.orElse(ImmutableList.of());
   }
 
   /**
@@ -907,7 +898,7 @@ public List<? extends OnModelErrorCallback> canonicalOnModelErrorCallbacks() {
    * <p>This method is only for use by Agent Development Kit.
    */
   public List<? extends BeforeToolCallback> canonicalBeforeToolCallbacks() {
-    return beforeToolCallback;
+    return beforeToolCallback.orElse(ImmutableList.of());
   }
 
   /**
@@ -916,7 +907,7 @@ public List<? extends BeforeToolCallback> canonicalBeforeToolCallbacks() {
    * <p>This method is only for use by Agent Development Kit.
    */
   public List<? extends AfterToolCallback> canonicalAfterToolCallbacks() {
-    return afterToolCallback;
+    return afterToolCallback.orElse(ImmutableList.of());
   }
 
   /**
@@ -925,7 +916,7 @@ public List<? extends AfterToolCallback> canonicalAfterToolCallbacks() {
    * <p>This method is only for use by Agent Development Kit.
    */
   public List<? extends OnToolErrorCallback> canonicalOnToolErrorCallbacks() {
-    return onToolErrorCallback;
+    return onToolErrorCallback.orElse(ImmutableList.of());
   }
 
   public Optional<Schema> inputSchema() {