feat: make stream_handler_executor publicly settable.

src/main/java/com/google/genai/ApiClient.java

@@ -404,15 +404,13 @@ private com.google.genai.interactions.core.ClientOptions createInteractionsClien
             .baseUrl(httpOptions.baseUrl())
             .apiKey(apiKey);
 
-    // BEGIN_SDK_PRIVATE_ONLY
-    // clientOptions
-    //     .flatMap(ClientOptions::streamHandlerExecutor)
-    //     .ifPresent(
-    //         streamHandlerExecutor -> {
-    //           com.google.genai.interactions.core.ClientOptions.Builder unused =
-    //               builder.streamHandlerExecutor(streamHandlerExecutor);
-    //         });
-    // END_SDK_PRIVATE_ONLY
+    clientOptions
+        .flatMap(ClientOptions::streamHandlerExecutor)
+        .ifPresent(
+            streamHandlerExecutor -> {
+              com.google.genai.interactions.core.ClientOptions.Builder unused =
+                  builder.streamHandlerExecutor(streamHandlerExecutor);
+            });
 
     httpOptions
         .apiVersion()

src/main/java/com/google/genai/types/ClientOptions.java

@@ -19,12 +19,14 @@
 package com.google.genai.types;
 
 import com.fasterxml.jackson.annotation.JsonCreator;
+import com.fasterxml.jackson.annotation.JsonIgnore;
 import com.fasterxml.jackson.annotation.JsonProperty;
 import com.fasterxml.jackson.databind.annotation.JsonDeserialize;
 import com.google.auto.value.AutoValue;
 import com.google.errorprone.annotations.CanIgnoreReturnValue;
 import com.google.genai.JsonSerializable;
 import java.util.Optional;
+import java.util.concurrent.Executor;
 
 /** Client options to be used in the client instantiation. */
 @AutoValue
@@ -42,6 +44,10 @@ public abstract class ClientOptions extends JsonSerializable {
   @JsonProperty("proxyOptions")
   public abstract Optional<ProxyOptions> proxyOptions();
 
+  /** EXPERIMENTAL the executor to use for running async stream handler callbacks. */
+  @JsonIgnore
+  public abstract Optional<Executor> streamHandlerExecutor();
+
   /** Instantiates a builder for ClientOptions. */
   @ExcludeFromGeneratedCoverageReport
   public static Builder builder() {
@@ -124,6 +130,25 @@ public Builder clearProxyOptions() {
       return proxyOptions(Optional.empty());
     }
 
+    /**
+     * Setter for streamHandlerExecutor.
+     *
+     * <p>streamHandlerExecutor: EXPERIMENTAL the executor to use for running async stream handler
+     * callbacks.
+     */
+    @JsonIgnore
+    public abstract Builder streamHandlerExecutor(Executor streamHandlerExecutor);
+
+    @ExcludeFromGeneratedCoverageReport
+    abstract Builder streamHandlerExecutor(Optional<Executor> streamHandlerExecutor);
+
+    /** Clears the value of streamHandlerExecutor field. */
+    @ExcludeFromGeneratedCoverageReport
+    @CanIgnoreReturnValue
+    public Builder clearStreamHandlerExecutor() {
+      return streamHandlerExecutor(Optional.empty());
+    }
+
     public abstract ClientOptions build();
   }
 

src/test/java/com/google/genai/HttpApiClientTest.java

@@ -1714,7 +1714,41 @@ public void testCloseClient() {
     assertTrue(client.httpClient().dispatcher().executorService().isShutdown());
     assertEquals(0, client.httpClient().connectionPool().connectionCount());
     if (client.interactionsClientOptions.streamHandlerExecutor() instanceof ExecutorService) {
-      assertTrue(((ExecutorService) client.interactionsClientOptions.streamHandlerExecutor()).isShutdown());
+      assertTrue(
+          ((ExecutorService) client.interactionsClientOptions.streamHandlerExecutor())
+              .isShutdown());
     }
   }
+
+  @Test
+  public void testCloseClient_withExecutorService() {
+    ExecutorService customExecutor = java.util.concurrent.Executors.newSingleThreadExecutor();
+    HttpApiClient client =
+        new HttpApiClient(
+            Optional.empty(),
+            Optional.of(PROJECT),
+            Optional.of(LOCATION),
+            Optional.of(CREDENTIALS),
+            Optional.empty(),
+            Optional.of(ClientOptions.builder().streamHandlerExecutor(customExecutor).build()));
+
+    client.close();
+
+    assertTrue(customExecutor.isShutdown());
+  }
+
+  @Test
+  public void testStreamHandlerExecutorPassthrough() {
+    java.util.concurrent.Executor customExecutor = Runnable::run;
+    HttpApiClient client =
+        new HttpApiClient(
+            Optional.empty(),
+            Optional.of(PROJECT),
+            Optional.of(LOCATION),
+            Optional.of(CREDENTIALS),
+            Optional.empty(),
+            Optional.of(ClientOptions.builder().streamHandlerExecutor(customExecutor).build()));
+
+    assertEquals(customExecutor, client.interactionsClientOptions.streamHandlerExecutor());
+  }
 }