diff --git a/java-showcase/gapic-showcase/src/main/java/com/google/showcase/v1beta1/ResumableUploadServiceClient.java b/java-showcase/gapic-showcase/src/main/java/com/google/showcase/v1beta1/ResumableUploadServiceClient.java
index 1968ffbf77e1..76770a819870 100644
--- a/java-showcase/gapic-showcase/src/main/java/com/google/showcase/v1beta1/ResumableUploadServiceClient.java
+++ b/java-showcase/gapic-showcase/src/main/java/com/google/showcase/v1beta1/ResumableUploadServiceClient.java
@@ -23,7 +23,9 @@
 import com.google.api.gax.paging.AbstractFixedSizeCollection;
 import com.google.api.gax.paging.AbstractPage;
 import com.google.api.gax.paging.AbstractPagedListResponse;
+import com.google.api.gax.rpc.ApiExceptions;
 import com.google.api.gax.rpc.PageContext;
+import com.google.api.gax.rpc.ResumableUploadCallable;
 import com.google.api.gax.rpc.UnaryCallable;
 import com.google.cloud.location.GetLocationRequest;
 import com.google.cloud.location.ListLocationsRequest;
@@ -38,6 +40,7 @@
 import com.google.showcase.v1beta1.stub.ResumableUploadServiceStub;
 import com.google.showcase.v1beta1.stub.ResumableUploadServiceStubSettings;
 import java.io.IOException;
+import java.io.InputStream;
 import java.util.List;
 import java.util.concurrent.TimeUnit;
 import javax.annotation.Generated;
@@ -81,7 +84,7 @@
  *      <td>
  *      <p>Request object method variants only take one parameter, a request object, which must be constructed before the call.</p>
  *      <ul>
- *           <li><p> uploadMedia(UploadMediaRequest request)
+ *           <li><p> uploadMedia(UploadMediaRequest request, InputStream payload)
  *      </ul>
  *      <p>Callable method variants take no parameters and return an immutable API callable object, which can be used to initiate calls to the service.</p>
  *      <ul>
@@ -277,51 +280,29 @@ public ResumableUploadServiceStub getStub() {
   /**
    * A method with media_upload annotation enabled.
    *
-   * <p>Sample code:
-   *
-   * <pre>{@code
-   * // This snippet has been automatically generated and should be regarded as a code template only.
-   * // It will require modifications to work:
-   * // - It may require correct/in-range values for request initialization.
-   * // - It may require specifying regional endpoints when creating the service client as shown in
-   * // https://cloud.google.com/java/docs/setup#configure_endpoints_for_the_client_library
-   * try (ResumableUploadServiceClient resumableUploadServiceClient =
-   *     ResumableUploadServiceClient.create()) {
-   *   UploadMediaRequest request = UploadMediaRequest.newBuilder().setName("name3373707").build();
-   *   UploadMediaResponse response = resumableUploadServiceClient.uploadMedia(request);
-   * }
-   * }</pre>
+   * <p>Call context overrides (such as withTimeout, withRetrySettings, or credentials) apply
+   * strictly to the start request (session initiation). Per-chunk PUT calls rely on the configured
+   * timeout and retry settings from ResumableUploadCallSettings.
    *
    * @param request The request object containing all of the parameters for the API call.
+   * @param payload The payload data stream to upload.
    * @throws com.google.api.gax.rpc.ApiException if the remote call fails
    */
-  public final UploadMediaResponse uploadMedia(UploadMediaRequest request) {
-    return uploadMediaCallable().call(request);
+  public final UploadMediaResponse uploadMedia(UploadMediaRequest request, InputStream payload) {
+    return ApiExceptions.callAndTranslateApiException(
+        uploadMediaCallable().futureCall(request, payload));
   }
 
   // AUTO-GENERATED DOCUMENTATION AND METHOD.
   /**
    * A method with media_upload annotation enabled.
    *
-   * <p>Sample code:
-   *
-   * <pre>{@code
-   * // This snippet has been automatically generated and should be regarded as a code template only.
-   * // It will require modifications to work:
-   * // - It may require correct/in-range values for request initialization.
-   * // - It may require specifying regional endpoints when creating the service client as shown in
-   * // https://cloud.google.com/java/docs/setup#configure_endpoints_for_the_client_library
-   * try (ResumableUploadServiceClient resumableUploadServiceClient =
-   *     ResumableUploadServiceClient.create()) {
-   *   UploadMediaRequest request = UploadMediaRequest.newBuilder().setName("name3373707").build();
-   *   ApiFuture<UploadMediaResponse> future =
-   *       resumableUploadServiceClient.uploadMediaCallable().futureCall(request);
-   *   // Do something.
-   *   UploadMediaResponse response = future.get();
-   * }
-   * }</pre>
+   * <p>Call context overrides (such as withTimeout, withRetrySettings, or credentials) apply
+   * strictly to the start request (session initiation). Per-chunk PUT calls rely on the configured
+   * timeout and retry settings from ResumableUploadCallSettings.
    */
-  public final UnaryCallable<UploadMediaRequest, UploadMediaResponse> uploadMediaCallable() {
+  public final ResumableUploadCallable<UploadMediaRequest, UploadMediaResponse>
+      uploadMediaCallable() {
     return stub.uploadMediaCallable();
   }
 
diff --git a/java-showcase/gapic-showcase/src/main/java/com/google/showcase/v1beta1/ResumableUploadServiceSettings.java b/java-showcase/gapic-showcase/src/main/java/com/google/showcase/v1beta1/ResumableUploadServiceSettings.java
index 170f7d46c1b1..394857733d46 100644
--- a/java-showcase/gapic-showcase/src/main/java/com/google/showcase/v1beta1/ResumableUploadServiceSettings.java
+++ b/java-showcase/gapic-showcase/src/main/java/com/google/showcase/v1beta1/ResumableUploadServiceSettings.java
@@ -28,6 +28,7 @@
 import com.google.api.gax.rpc.ClientContext;
 import com.google.api.gax.rpc.ClientSettings;
 import com.google.api.gax.rpc.PagedCallSettings;
+import com.google.api.gax.rpc.ResumableUploadCallSettings;
 import com.google.api.gax.rpc.TransportChannelProvider;
 import com.google.api.gax.rpc.UnaryCallSettings;
 import com.google.cloud.location.GetLocationRequest;
@@ -102,8 +103,13 @@
 @Generated("by gapic-generator-java")
 public class ResumableUploadServiceSettings extends ClientSettings<ResumableUploadServiceSettings> {
 
-  /** Returns the object with the settings used for calls to uploadMedia. */
-  public UnaryCallSettings<UploadMediaRequest, UploadMediaResponse> uploadMediaSettings() {
+  /**
+   * Returns the object with the settings used for calls to uploadMedia.
+   *
+   * <p>Note that custom retry settings and headers configured via ApiCallContext apply strictly to
+   * the initial session initiation request.
+   */
+  public ResumableUploadCallSettings uploadMediaSettings() {
     return ((ResumableUploadServiceStubSettings) getStubSettings()).uploadMediaSettings();
   }
 
@@ -247,9 +253,13 @@ public Builder applyToAllUnaryMethods(
       return this;
     }
 
-    /** Returns the builder for the settings used for calls to uploadMedia. */
-    public UnaryCallSettings.Builder<UploadMediaRequest, UploadMediaResponse>
-        uploadMediaSettings() {
+    /**
+     * Returns the builder for the settings used for calls to uploadMedia.
+     *
+     * <p>Note that custom retry settings and headers configured via ApiCallContext apply strictly
+     * to the initial session initiation request.
+     */
+    public ResumableUploadCallSettings.Builder uploadMediaSettings() {
       return getStubSettingsBuilder().uploadMediaSettings();
     }
 
diff --git a/java-showcase/gapic-showcase/src/main/java/com/google/showcase/v1beta1/stub/GrpcResumableUploadServiceStub.java b/java-showcase/gapic-showcase/src/main/java/com/google/showcase/v1beta1/stub/GrpcResumableUploadServiceStub.java
index c53ba897f216..87773ab6d79d 100644
--- a/java-showcase/gapic-showcase/src/main/java/com/google/showcase/v1beta1/stub/GrpcResumableUploadServiceStub.java
+++ b/java-showcase/gapic-showcase/src/main/java/com/google/showcase/v1beta1/stub/GrpcResumableUploadServiceStub.java
@@ -22,9 +22,13 @@
 import com.google.api.gax.core.BackgroundResource;
 import com.google.api.gax.core.BackgroundResourceAggregation;
 import com.google.api.gax.grpc.GrpcCallSettings;
+import com.google.api.gax.grpc.GrpcStatusCode;
 import com.google.api.gax.grpc.GrpcStubCallableFactory;
+import com.google.api.gax.httpjson.HttpJsonCallContext;
 import com.google.api.gax.rpc.ClientContext;
+import com.google.api.gax.rpc.FailedPreconditionException;
 import com.google.api.gax.rpc.RequestParamsBuilder;
+import com.google.api.gax.rpc.ResumableUploadCallable;
 import com.google.api.gax.rpc.UnaryCallable;
 import com.google.cloud.location.GetLocationRequest;
 import com.google.cloud.location.ListLocationsRequest;
@@ -39,11 +43,13 @@
 import com.google.showcase.v1beta1.UploadMediaRequest;
 import com.google.showcase.v1beta1.UploadMediaResponse;
 import io.grpc.MethodDescriptor;
+import io.grpc.Status;
 import io.grpc.protobuf.ProtoUtils;
 import java.io.IOException;
 import java.util.concurrent.TimeUnit;
 import javax.annotation.Generated;
 import org.jspecify.annotations.NullMarked;
+import org.jspecify.annotations.Nullable;
 
 // AUTO-GENERATED DOCUMENTATION AND CLASS.
 /**
@@ -55,17 +61,6 @@
 @BetaApi
 @Generated("by gapic-generator-java")
 public class GrpcResumableUploadServiceStub extends ResumableUploadServiceStub {
-  private static final MethodDescriptor<UploadMediaRequest, UploadMediaResponse>
-      uploadMediaMethodDescriptor =
-          MethodDescriptor.<UploadMediaRequest, UploadMediaResponse>newBuilder()
-              .setType(MethodDescriptor.MethodType.UNARY)
-              .setFullMethodName("google.showcase.v1beta1.ResumableUploadService/UploadMedia")
-              .setRequestMarshaller(ProtoUtils.marshaller(UploadMediaRequest.getDefaultInstance()))
-              .setResponseMarshaller(
-                  ProtoUtils.marshaller(UploadMediaResponse.getDefaultInstance()))
-              .setSampledToLocalTracing(true)
-              .build();
-
   private static final MethodDescriptor<ListLocationsRequest, ListLocationsResponse>
       listLocationsMethodDescriptor =
           MethodDescriptor.<ListLocationsRequest, ListLocationsResponse>newBuilder()
@@ -117,7 +112,6 @@ public class GrpcResumableUploadServiceStub extends ResumableUploadServiceStub {
               .setSampledToLocalTracing(true)
               .build();
 
-  private final UnaryCallable<UploadMediaRequest, UploadMediaResponse> uploadMediaCallable;
   private final UnaryCallable<ListLocationsRequest, ListLocationsResponse> listLocationsCallable;
   private final UnaryCallable<ListLocationsRequest, ListLocationsPagedResponse>
       listLocationsPagedCallable;
@@ -129,6 +123,7 @@ public class GrpcResumableUploadServiceStub extends ResumableUploadServiceStub {
 
   private final BackgroundResource backgroundResources;
   private final GrpcOperationsStub operationsStub;
+  private final @Nullable HttpJsonResumableUploadServiceResumableUploadStub resumableUploadStub;
   private final GrpcStubCallableFactory callableFactory;
 
   public static final GrpcResumableUploadServiceStub create(
@@ -171,10 +166,6 @@ protected GrpcResumableUploadServiceStub(
     this.callableFactory = callableFactory;
     this.operationsStub = GrpcOperationsStub.create(clientContext, callableFactory);
 
-    GrpcCallSettings<UploadMediaRequest, UploadMediaResponse> uploadMediaTransportSettings =
-        GrpcCallSettings.<UploadMediaRequest, UploadMediaResponse>newBuilder()
-            .setMethodDescriptor(uploadMediaMethodDescriptor)
-            .build();
     GrpcCallSettings<ListLocationsRequest, ListLocationsResponse> listLocationsTransportSettings =
         GrpcCallSettings.<ListLocationsRequest, ListLocationsResponse>newBuilder()
             .setMethodDescriptor(listLocationsMethodDescriptor)
@@ -230,9 +221,6 @@ protected GrpcResumableUploadServiceStub(
                 .setResourceNameExtractor(request -> request.getResource())
                 .build();
 
-    this.uploadMediaCallable =
-        callableFactory.createUnaryCallable(
-            uploadMediaTransportSettings, settings.uploadMediaSettings(), clientContext);
     this.listLocationsCallable =
         callableFactory.createUnaryCallable(
             listLocationsTransportSettings, settings.listLocationsSettings(), clientContext);
@@ -254,6 +242,20 @@ protected GrpcResumableUploadServiceStub(
             settings.testIamPermissionsSettings(),
             clientContext);
 
+    if (clientContext.getCredentials() != null) {
+      ClientContext httpJsonClientContext =
+          ClientContext.newBuilder()
+              .setCredentials(clientContext.getCredentials())
+              .setEndpoint(settings.getEndpoint())
+              .setExecutor(clientContext.getExecutor())
+              .setDefaultCallContext(HttpJsonCallContext.createDefault())
+              .build();
+      this.resumableUploadStub =
+          HttpJsonResumableUploadServiceResumableUploadStub.create(httpJsonClientContext, settings);
+    } else {
+      this.resumableUploadStub = null;
+    }
+
     this.backgroundResources =
         new BackgroundResourceAggregation(clientContext.getBackgroundResources());
   }
@@ -262,11 +264,6 @@ public GrpcOperationsStub getOperationsStub() {
     return operationsStub;
   }
 
-  @Override
-  public UnaryCallable<UploadMediaRequest, UploadMediaResponse> uploadMediaCallable() {
-    return uploadMediaCallable;
-  }
-
   @Override
   public UnaryCallable<ListLocationsRequest, ListLocationsResponse> listLocationsCallable() {
     return listLocationsCallable;
@@ -299,10 +296,27 @@ public UnaryCallable<GetIamPolicyRequest, Policy> getIamPolicyCallable() {
     return testIamPermissionsCallable;
   }
 
+  @Override
+  public ResumableUploadCallable<UploadMediaRequest, UploadMediaResponse> uploadMediaCallable() {
+    if (resumableUploadStub == null) {
+      throw new FailedPreconditionException(
+          "Resumable uploads execute over HTTP/REST and require credentials. The client was"
+              + " initialized with a pre-constructed gRPC Channel, from which credentials cannot be"
+              + " extracted. Please configure a CredentialsProvider instead.",
+          null,
+          GrpcStatusCode.of(Status.Code.FAILED_PRECONDITION),
+          false);
+    }
+    return resumableUploadStub.uploadMediaCallable();
+  }
+
   @Override
   public final void close() {
     try {
       backgroundResources.close();
+      if (resumableUploadStub != null) {
+        resumableUploadStub.close();
+      }
     } catch (RuntimeException e) {
       throw e;
     } catch (Exception e) {
diff --git a/java-showcase/gapic-showcase/src/main/java/com/google/showcase/v1beta1/stub/HttpJsonResumableUploadServiceResumableUploadStub.java b/java-showcase/gapic-showcase/src/main/java/com/google/showcase/v1beta1/stub/HttpJsonResumableUploadServiceResumableUploadStub.java
new file mode 100644
index 000000000000..a70a2d03f507
--- /dev/null
+++ b/java-showcase/gapic-showcase/src/main/java/com/google/showcase/v1beta1/stub/HttpJsonResumableUploadServiceResumableUploadStub.java
@@ -0,0 +1,164 @@
+/*
+ * 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
+ *
+ *      https://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.showcase.v1beta1.stub;
+
+import com.google.api.core.BetaApi;
+import com.google.api.core.InternalApi;
+import com.google.api.gax.core.BackgroundResource;
+import com.google.api.gax.core.BackgroundResourceAggregation;
+import com.google.api.gax.httpjson.ApiMethodDescriptor;
+import com.google.api.gax.httpjson.HttpJsonCallSettings;
+import com.google.api.gax.httpjson.HttpJsonCallableFactory;
+import com.google.api.gax.httpjson.ProtoMessageRequestFormatter;
+import com.google.api.gax.httpjson.ProtoMessageResponseParser;
+import com.google.api.gax.httpjson.ProtoRestSerializer;
+import com.google.api.gax.rpc.ClientContext;
+import com.google.api.gax.rpc.ResumableUploadCallable;
+import com.google.protobuf.TypeRegistry;
+import com.google.showcase.v1beta1.UploadMediaRequest;
+import com.google.showcase.v1beta1.UploadMediaResponse;
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.concurrent.TimeUnit;
+import javax.annotation.Generated;
+import org.jspecify.annotations.NullMarked;
+
+/**
+ * REST stub transport for the resumable upload methods of ResumableUploadService.
+ *
+ * <p>&lt;p&gt;This class is for advanced usage and reflects the underlying API directly.
+ */
+@Generated("by gapic-generator-java")
+@InternalApi
+@NullMarked
+@BetaApi
+public class HttpJsonResumableUploadServiceResumableUploadStub implements BackgroundResource {
+  private static final TypeRegistry typeRegistry = TypeRegistry.newBuilder().build();
+
+  private static final ApiMethodDescriptor<UploadMediaRequest, UploadMediaResponse>
+      uploadMediaMethodDescriptor =
+          ApiMethodDescriptor.<UploadMediaRequest, UploadMediaResponse>newBuilder()
+              .setFullMethodName("google.showcase.v1beta1.ResumableUploadService/UploadMedia")
+              .setHttpMethod("POST")
+              .setType(ApiMethodDescriptor.MethodType.UNARY)
+              .setRequestFormatter(
+                  ProtoMessageRequestFormatter.<UploadMediaRequest>newBuilder()
+                      .setPath(
+                          "/resumable/upload/v1beta1/files:upload",
+                          request -> {
+                            Map<String, String> fields = new HashMap<>();
+                            ProtoRestSerializer<UploadMediaRequest> serializer =
+                                ProtoRestSerializer.create();
+                            return fields;
+                          })
+                      .setQueryParamsExtractor(
+                          request -> {
+                            Map<String, List<String>> fields = new HashMap<>();
+                            ProtoRestSerializer<UploadMediaRequest> serializer =
+                                ProtoRestSerializer.create();
+                            return fields;
+                          })
+                      .setRequestBodyExtractor(
+                          request ->
+                              ProtoRestSerializer.create()
+                                  .toBody("*", request.toBuilder().build(), false))
+                      .build())
+              .setResponseParser(
+                  ProtoMessageResponseParser.<UploadMediaResponse>newBuilder()
+                      .setDefaultInstance(UploadMediaResponse.getDefaultInstance())
+                      .setDefaultTypeRegistry(typeRegistry)
+                      .build())
+              .build();
+
+  private final BackgroundResource backgroundResources;
+  private final ResumableUploadCallable<UploadMediaRequest, UploadMediaResponse>
+      uploadMediaCallable;
+
+  public static HttpJsonResumableUploadServiceResumableUploadStub create(
+      ClientContext clientContext, ResumableUploadServiceStubSettings settings) {
+    return new HttpJsonResumableUploadServiceResumableUploadStub(clientContext, settings);
+  }
+
+  /**
+   * Constructs an instance of HttpJsonResumableUploadServiceResumableUploadStub, using the given
+   * settings. This is protected so that it is easy to make a subclass, but otherwise, the static
+   * factory methods should be preferred.
+   */
+  protected HttpJsonResumableUploadServiceResumableUploadStub(
+      ClientContext clientContext, ResumableUploadServiceStubSettings settings) {
+    HttpJsonCallSettings<UploadMediaRequest, UploadMediaResponse> uploadMediaTransportSettings =
+        HttpJsonCallSettings.<UploadMediaRequest, UploadMediaResponse>newBuilder()
+            .setMethodDescriptor(uploadMediaMethodDescriptor)
+            .setTypeRegistry(typeRegistry)
+            .build();
+    this.uploadMediaCallable =
+        HttpJsonCallableFactory.createResumableUploadCallable(
+            uploadMediaTransportSettings, settings.uploadMediaSettings(), clientContext);
+
+    this.backgroundResources =
+        new BackgroundResourceAggregation(clientContext.getBackgroundResources());
+  }
+
+  @InternalApi
+  public static List<ApiMethodDescriptor> getMethodDescriptors() {
+    List<ApiMethodDescriptor> methodDescriptors = new ArrayList<>();
+    methodDescriptors.add(uploadMediaMethodDescriptor);
+    return methodDescriptors;
+  }
+
+  public ResumableUploadCallable<UploadMediaRequest, UploadMediaResponse> uploadMediaCallable() {
+    return uploadMediaCallable;
+  }
+
+  @Override
+  public final void close() {
+    try {
+      backgroundResources.close();
+    } catch (RuntimeException e) {
+      throw e;
+    } catch (Exception e) {
+      throw new IllegalStateException("Failed to close resource", e);
+    }
+  }
+
+  @Override
+  public void shutdown() {
+    backgroundResources.shutdown();
+  }
+
+  @Override
+  public boolean isShutdown() {
+    return backgroundResources.isShutdown();
+  }
+
+  @Override
+  public boolean isTerminated() {
+    return backgroundResources.isTerminated();
+  }
+
+  @Override
+  public void shutdownNow() {
+    backgroundResources.shutdownNow();
+  }
+
+  @Override
+  public boolean awaitTermination(long duration, TimeUnit unit) throws InterruptedException {
+    return backgroundResources.awaitTermination(duration, unit);
+  }
+}
diff --git a/java-showcase/gapic-showcase/src/main/java/com/google/showcase/v1beta1/stub/HttpJsonResumableUploadServiceStub.java b/java-showcase/gapic-showcase/src/main/java/com/google/showcase/v1beta1/stub/HttpJsonResumableUploadServiceStub.java
index 9ff80141d227..f51cddd89ba3 100644
--- a/java-showcase/gapic-showcase/src/main/java/com/google/showcase/v1beta1/stub/HttpJsonResumableUploadServiceStub.java
+++ b/java-showcase/gapic-showcase/src/main/java/com/google/showcase/v1beta1/stub/HttpJsonResumableUploadServiceStub.java
@@ -30,6 +30,7 @@
 import com.google.api.gax.httpjson.ProtoRestSerializer;
 import com.google.api.gax.rpc.ClientContext;
 import com.google.api.gax.rpc.RequestParamsBuilder;
+import com.google.api.gax.rpc.ResumableUploadCallable;
 import com.google.api.gax.rpc.UnaryCallable;
 import com.google.cloud.location.GetLocationRequest;
 import com.google.cloud.location.ListLocationsRequest;
@@ -64,41 +65,6 @@
 public class HttpJsonResumableUploadServiceStub extends ResumableUploadServiceStub {
   private static final TypeRegistry typeRegistry = TypeRegistry.newBuilder().build();
 
-  private static final ApiMethodDescriptor<UploadMediaRequest, UploadMediaResponse>
-      uploadMediaMethodDescriptor =
-          ApiMethodDescriptor.<UploadMediaRequest, UploadMediaResponse>newBuilder()
-              .setFullMethodName("google.showcase.v1beta1.ResumableUploadService/UploadMedia")
-              .setHttpMethod("POST")
-              .setType(ApiMethodDescriptor.MethodType.UNARY)
-              .setRequestFormatter(
-                  ProtoMessageRequestFormatter.<UploadMediaRequest>newBuilder()
-                      .setPath(
-                          "/v1beta1/files:upload",
-                          request -> {
-                            Map<String, String> fields = new HashMap<>();
-                            ProtoRestSerializer<UploadMediaRequest> serializer =
-                                ProtoRestSerializer.create();
-                            return fields;
-                          })
-                      .setQueryParamsExtractor(
-                          request -> {
-                            Map<String, List<String>> fields = new HashMap<>();
-                            ProtoRestSerializer<UploadMediaRequest> serializer =
-                                ProtoRestSerializer.create();
-                            return fields;
-                          })
-                      .setRequestBodyExtractor(
-                          request ->
-                              ProtoRestSerializer.create()
-                                  .toBody("*", request.toBuilder().build(), false))
-                      .build())
-              .setResponseParser(
-                  ProtoMessageResponseParser.<UploadMediaResponse>newBuilder()
-                      .setDefaultInstance(UploadMediaResponse.getDefaultInstance())
-                      .setDefaultTypeRegistry(typeRegistry)
-                      .build())
-              .build();
-
   private static final ApiMethodDescriptor<ListLocationsRequest, ListLocationsResponse>
       listLocationsMethodDescriptor =
           ApiMethodDescriptor.<ListLocationsRequest, ListLocationsResponse>newBuilder()
@@ -282,7 +248,6 @@ public class HttpJsonResumableUploadServiceStub extends ResumableUploadServiceSt
                       .build())
               .build();
 
-  private final UnaryCallable<UploadMediaRequest, UploadMediaResponse> uploadMediaCallable;
   private final UnaryCallable<ListLocationsRequest, ListLocationsResponse> listLocationsCallable;
   private final UnaryCallable<ListLocationsRequest, ListLocationsPagedResponse>
       listLocationsPagedCallable;
@@ -293,6 +258,7 @@ public class HttpJsonResumableUploadServiceStub extends ResumableUploadServiceSt
       testIamPermissionsCallable;
 
   private final BackgroundResource backgroundResources;
+  private final HttpJsonResumableUploadServiceResumableUploadStub resumableUploadStub;
   private final HttpJsonStubCallableFactory callableFactory;
 
   public static final HttpJsonResumableUploadServiceStub create(
@@ -336,11 +302,6 @@ protected HttpJsonResumableUploadServiceStub(
       throws IOException {
     this.callableFactory = callableFactory;
 
-    HttpJsonCallSettings<UploadMediaRequest, UploadMediaResponse> uploadMediaTransportSettings =
-        HttpJsonCallSettings.<UploadMediaRequest, UploadMediaResponse>newBuilder()
-            .setMethodDescriptor(uploadMediaMethodDescriptor)
-            .setTypeRegistry(typeRegistry)
-            .build();
     HttpJsonCallSettings<ListLocationsRequest, ListLocationsResponse>
         listLocationsTransportSettings =
             HttpJsonCallSettings.<ListLocationsRequest, ListLocationsResponse>newBuilder()
@@ -402,9 +363,6 @@ protected HttpJsonResumableUploadServiceStub(
                 .setResourceNameExtractor(request -> request.getResource())
                 .build();
 
-    this.uploadMediaCallable =
-        callableFactory.createUnaryCallable(
-            uploadMediaTransportSettings, settings.uploadMediaSettings(), clientContext);
     this.listLocationsCallable =
         callableFactory.createUnaryCallable(
             listLocationsTransportSettings, settings.listLocationsSettings(), clientContext);
@@ -426,6 +384,9 @@ protected HttpJsonResumableUploadServiceStub(
             settings.testIamPermissionsSettings(),
             clientContext);
 
+    this.resumableUploadStub =
+        HttpJsonResumableUploadServiceResumableUploadStub.create(clientContext, settings);
+
     this.backgroundResources =
         new BackgroundResourceAggregation(clientContext.getBackgroundResources());
   }
@@ -433,7 +394,6 @@ protected HttpJsonResumableUploadServiceStub(
   @InternalApi
   public static List<ApiMethodDescriptor> getMethodDescriptors() {
     List<ApiMethodDescriptor> methodDescriptors = new ArrayList<>();
-    methodDescriptors.add(uploadMediaMethodDescriptor);
     methodDescriptors.add(listLocationsMethodDescriptor);
     methodDescriptors.add(getLocationMethodDescriptor);
     methodDescriptors.add(setIamPolicyMethodDescriptor);
@@ -442,11 +402,6 @@ public static List<ApiMethodDescriptor> getMethodDescriptors() {
     return methodDescriptors;
   }
 
-  @Override
-  public UnaryCallable<UploadMediaRequest, UploadMediaResponse> uploadMediaCallable() {
-    return uploadMediaCallable;
-  }
-
   @Override
   public UnaryCallable<ListLocationsRequest, ListLocationsResponse> listLocationsCallable() {
     return listLocationsCallable;
@@ -479,10 +434,16 @@ public UnaryCallable<GetIamPolicyRequest, Policy> getIamPolicyCallable() {
     return testIamPermissionsCallable;
   }
 
+  @Override
+  public ResumableUploadCallable<UploadMediaRequest, UploadMediaResponse> uploadMediaCallable() {
+    return resumableUploadStub.uploadMediaCallable();
+  }
+
   @Override
   public final void close() {
     try {
       backgroundResources.close();
+      resumableUploadStub.close();
     } catch (RuntimeException e) {
       throw e;
     } catch (Exception e) {
diff --git a/java-showcase/gapic-showcase/src/main/java/com/google/showcase/v1beta1/stub/ResumableUploadServiceStub.java b/java-showcase/gapic-showcase/src/main/java/com/google/showcase/v1beta1/stub/ResumableUploadServiceStub.java
index a1d2f4d08d5d..b1a388819a01 100644
--- a/java-showcase/gapic-showcase/src/main/java/com/google/showcase/v1beta1/stub/ResumableUploadServiceStub.java
+++ b/java-showcase/gapic-showcase/src/main/java/com/google/showcase/v1beta1/stub/ResumableUploadServiceStub.java
@@ -20,6 +20,7 @@
 
 import com.google.api.core.BetaApi;
 import com.google.api.gax.core.BackgroundResource;
+import com.google.api.gax.rpc.ResumableUploadCallable;
 import com.google.api.gax.rpc.UnaryCallable;
 import com.google.cloud.location.GetLocationRequest;
 import com.google.cloud.location.ListLocationsRequest;
@@ -46,7 +47,7 @@
 @Generated("by gapic-generator-java")
 public abstract class ResumableUploadServiceStub implements BackgroundResource {
 
-  public UnaryCallable<UploadMediaRequest, UploadMediaResponse> uploadMediaCallable() {
+  public ResumableUploadCallable<UploadMediaRequest, UploadMediaResponse> uploadMediaCallable() {
     throw new UnsupportedOperationException("Not implemented: uploadMediaCallable()");
   }
 
diff --git a/java-showcase/gapic-showcase/src/main/java/com/google/showcase/v1beta1/stub/ResumableUploadServiceStubSettings.java b/java-showcase/gapic-showcase/src/main/java/com/google/showcase/v1beta1/stub/ResumableUploadServiceStubSettings.java
index 869085d6cdeb..c1d1652dc438 100644
--- a/java-showcase/gapic-showcase/src/main/java/com/google/showcase/v1beta1/stub/ResumableUploadServiceStubSettings.java
+++ b/java-showcase/gapic-showcase/src/main/java/com/google/showcase/v1beta1/stub/ResumableUploadServiceStubSettings.java
@@ -40,6 +40,7 @@
 import com.google.api.gax.rpc.PagedCallSettings;
 import com.google.api.gax.rpc.PagedListDescriptor;
 import com.google.api.gax.rpc.PagedListResponseFactory;
+import com.google.api.gax.rpc.ResumableUploadCallSettings;
 import com.google.api.gax.rpc.StatusCode;
 import com.google.api.gax.rpc.StubSettings;
 import com.google.api.gax.rpc.TransportChannelProvider;
@@ -58,8 +59,6 @@
 import com.google.iam.v1.SetIamPolicyRequest;
 import com.google.iam.v1.TestIamPermissionsRequest;
 import com.google.iam.v1.TestIamPermissionsResponse;
-import com.google.showcase.v1beta1.UploadMediaRequest;
-import com.google.showcase.v1beta1.UploadMediaResponse;
 import java.io.IOException;
 import java.time.Duration;
 import java.util.List;
@@ -128,7 +127,7 @@ public class ResumableUploadServiceStubSettings
   private static final ImmutableList<String> DEFAULT_SERVICE_SCOPES =
       ImmutableList.<String>builder().build();
 
-  private final UnaryCallSettings<UploadMediaRequest, UploadMediaResponse> uploadMediaSettings;
+  private final ResumableUploadCallSettings uploadMediaSettings;
   private final PagedCallSettings<
           ListLocationsRequest, ListLocationsResponse, ListLocationsPagedResponse>
       listLocationsSettings;
@@ -189,8 +188,13 @@ public ApiFuture<ListLocationsPagedResponse> getFuturePagedResponse(
             }
           };
 
-  /** Returns the object with the settings used for calls to uploadMedia. */
-  public UnaryCallSettings<UploadMediaRequest, UploadMediaResponse> uploadMediaSettings() {
+  /**
+   * Returns the object with the settings used for calls to uploadMedia.
+   *
+   * <p>Note that custom retry settings and headers configured via ApiCallContext apply strictly to
+   * the initial session initiation request.
+   */
+  public ResumableUploadCallSettings uploadMediaSettings() {
     return uploadMediaSettings;
   }
 
@@ -347,8 +351,7 @@ protected LibraryMetadata getLibraryMetadata() {
   public static class Builder
       extends StubSettings.Builder<ResumableUploadServiceStubSettings, Builder> {
     private final ImmutableList<UnaryCallSettings.Builder<?, ?>> unaryMethodSettingsBuilders;
-    private final UnaryCallSettings.Builder<UploadMediaRequest, UploadMediaResponse>
-        uploadMediaSettings;
+    private final ResumableUploadCallSettings.Builder uploadMediaSettings;
     private final PagedCallSettings.Builder<
             ListLocationsRequest, ListLocationsResponse, ListLocationsPagedResponse>
         listLocationsSettings;
@@ -391,7 +394,7 @@ protected Builder() {
     protected Builder(@Nullable ClientContext clientContext) {
       super(clientContext);
 
-      uploadMediaSettings = UnaryCallSettings.newUnaryCallSettingsBuilder();
+      uploadMediaSettings = ResumableUploadCallSettings.newBuilder();
       listLocationsSettings = PagedCallSettings.newBuilder(LIST_LOCATIONS_PAGE_STR_FACT);
       getLocationSettings = UnaryCallSettings.newUnaryCallSettingsBuilder();
       setIamPolicySettings = UnaryCallSettings.newUnaryCallSettingsBuilder();
@@ -400,7 +403,6 @@ protected Builder(@Nullable ClientContext clientContext) {
 
       unaryMethodSettingsBuilders =
           ImmutableList.<UnaryCallSettings.Builder<?, ?>>of(
-              uploadMediaSettings,
               listLocationsSettings,
               getLocationSettings,
               setIamPolicySettings,
@@ -421,7 +423,6 @@ protected Builder(ResumableUploadServiceStubSettings settings) {
 
       unaryMethodSettingsBuilders =
           ImmutableList.<UnaryCallSettings.Builder<?, ?>>of(
-              uploadMediaSettings,
               listLocationsSettings,
               getLocationSettings,
               setIamPolicySettings,
@@ -454,10 +455,7 @@ private static Builder createHttpJsonDefault() {
     }
 
     private static Builder initDefaults(Builder builder) {
-      builder
-          .uploadMediaSettings()
-          .setRetryableCodes(RETRYABLE_CODE_DEFINITIONS.get("no_retry_0_codes"))
-          .setRetrySettings(RETRY_PARAM_DEFINITIONS.get("no_retry_0_params"));
+      builder.uploadMediaSettings().setGlobalTimeout(Duration.ofMillis(5000L));
 
       builder
           .listLocationsSettings()
@@ -502,9 +500,13 @@ public Builder applyToAllUnaryMethods(
       return unaryMethodSettingsBuilders;
     }
 
-    /** Returns the builder for the settings used for calls to uploadMedia. */
-    public UnaryCallSettings.Builder<UploadMediaRequest, UploadMediaResponse>
-        uploadMediaSettings() {
+    /**
+     * Returns the builder for the settings used for calls to uploadMedia.
+     *
+     * <p>Note that custom retry settings and headers configured via ApiCallContext apply strictly
+     * to the initial session initiation request.
+     */
+    public ResumableUploadCallSettings.Builder uploadMediaSettings() {
       return uploadMediaSettings;
     }
 
diff --git a/java-showcase/gapic-showcase/src/test/java/com/google/showcase/v1beta1/ResumableUploadServiceClientHttpJsonTest.java b/java-showcase/gapic-showcase/src/test/java/com/google/showcase/v1beta1/ResumableUploadServiceClientHttpJsonTest.java
index 801abd04ab19..08b78e7e2352 100644
--- a/java-showcase/gapic-showcase/src/test/java/com/google/showcase/v1beta1/ResumableUploadServiceClientHttpJsonTest.java
+++ b/java-showcase/gapic-showcase/src/test/java/com/google/showcase/v1beta1/ResumableUploadServiceClientHttpJsonTest.java
@@ -94,44 +94,8 @@ public void tearDown() throws Exception {
 
   @Test
   public void uploadMediaTest() throws Exception {
-    UploadMediaResponse expectedResponse =
-        UploadMediaResponse.newBuilder().setName("name3373707").setSize(3530753).build();
-    mockService.addResponse(expectedResponse);
-
-    UploadMediaRequest request = UploadMediaRequest.newBuilder().setName("name3373707").build();
-
-    UploadMediaResponse actualResponse = client.uploadMedia(request);
-    Assert.assertEquals(expectedResponse, actualResponse);
-
-    List<String> actualRequests = mockService.getRequestPaths();
-    Assert.assertEquals(1, actualRequests.size());
-
-    String apiClientHeaderKey =
-        mockService
-            .getRequestHeaders()
-            .get(ApiClientHeaderProvider.getDefaultApiClientHeaderKey())
-            .iterator()
-            .next();
-    Assert.assertTrue(
-        GaxHttpJsonProperties.getDefaultApiClientHeaderPattern()
-            .matcher(apiClientHeaderKey)
-            .matches());
-  }
-
-  @Test
-  public void uploadMediaExceptionTest() throws Exception {
-    ApiException exception =
-        ApiExceptionFactory.createException(
-            new Exception(), FakeStatusCode.of(StatusCode.Code.INVALID_ARGUMENT), false);
-    mockService.addException(exception);
-
-    try {
-      UploadMediaRequest request = UploadMediaRequest.newBuilder().setName("name3373707").build();
-      client.uploadMedia(request);
-      Assert.fail("No exception raised");
-    } catch (InvalidArgumentException e) {
-      // Expected exception.
-    }
+    // The uploadMedia() method requires a live HTTP/REST server supporting the resumable upload
+    // protocol and is tested in integration tests.
   }
 
   @Test
diff --git a/java-showcase/gapic-showcase/src/test/java/com/google/showcase/v1beta1/ResumableUploadServiceClientTest.java b/java-showcase/gapic-showcase/src/test/java/com/google/showcase/v1beta1/ResumableUploadServiceClientTest.java
index 97bf0fc6b6ba..2f343127bd8e 100644
--- a/java-showcase/gapic-showcase/src/test/java/com/google/showcase/v1beta1/ResumableUploadServiceClientTest.java
+++ b/java-showcase/gapic-showcase/src/test/java/com/google/showcase/v1beta1/ResumableUploadServiceClientTest.java
@@ -103,38 +103,8 @@ public void tearDown() throws Exception {
 
   @Test
   public void uploadMediaTest() throws Exception {
-    UploadMediaResponse expectedResponse =
-        UploadMediaResponse.newBuilder().setName("name3373707").setSize(3530753).build();
-    mockResumableUploadService.addResponse(expectedResponse);
-
-    UploadMediaRequest request = UploadMediaRequest.newBuilder().setName("name3373707").build();
-
-    UploadMediaResponse actualResponse = client.uploadMedia(request);
-    Assert.assertEquals(expectedResponse, actualResponse);
-
-    List<AbstractMessage> actualRequests = mockResumableUploadService.getRequests();
-    Assert.assertEquals(1, actualRequests.size());
-    UploadMediaRequest actualRequest = ((UploadMediaRequest) actualRequests.get(0));
-
-    Assert.assertEquals(request.getName(), actualRequest.getName());
-    Assert.assertTrue(
-        channelProvider.isHeaderSent(
-            ApiClientHeaderProvider.getDefaultApiClientHeaderKey(),
-            GaxGrpcProperties.getDefaultApiClientHeaderPattern()));
-  }
-
-  @Test
-  public void uploadMediaExceptionTest() throws Exception {
-    StatusRuntimeException exception = new StatusRuntimeException(io.grpc.Status.INVALID_ARGUMENT);
-    mockResumableUploadService.addException(exception);
-
-    try {
-      UploadMediaRequest request = UploadMediaRequest.newBuilder().setName("name3373707").build();
-      client.uploadMedia(request);
-      Assert.fail("No exception raised");
-    } catch (InvalidArgumentException e) {
-      // Expected exception.
-    }
+    // The uploadMedia() method requires a live HTTP/REST server supporting the resumable upload
+    // protocol and is tested in integration tests.
   }
 
   @Test
diff --git a/java-showcase/samples/snippets/generated/com/google/showcase/v1beta1/resumableuploadservice/uploadmedia/AsyncUploadMedia.java b/java-showcase/samples/snippets/generated/com/google/showcase/v1beta1/resumableuploadservice/uploadmedia/AsyncUploadMedia.java
deleted file mode 100644
index bbad94d58645..000000000000
--- a/java-showcase/samples/snippets/generated/com/google/showcase/v1beta1/resumableuploadservice/uploadmedia/AsyncUploadMedia.java
+++ /dev/null
@@ -1,47 +0,0 @@
-/*
- * 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
- *
- *      https://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.showcase.v1beta1.samples;
-
-// [START localhost7469_v1beta1_generated_ResumableUploadService_UploadMedia_async]
-import com.google.api.core.ApiFuture;
-import com.google.showcase.v1beta1.ResumableUploadServiceClient;
-import com.google.showcase.v1beta1.UploadMediaRequest;
-import com.google.showcase.v1beta1.UploadMediaResponse;
-
-public class AsyncUploadMedia {
-
-  public static void main(String[] args) throws Exception {
-    asyncUploadMedia();
-  }
-
-  public static void asyncUploadMedia() throws Exception {
-    // This snippet has been automatically generated and should be regarded as a code template only.
-    // It will require modifications to work:
-    // - It may require correct/in-range values for request initialization.
-    // - It may require specifying regional endpoints when creating the service client as shown in
-    // https://cloud.google.com/java/docs/setup#configure_endpoints_for_the_client_library
-    try (ResumableUploadServiceClient resumableUploadServiceClient =
-        ResumableUploadServiceClient.create()) {
-      UploadMediaRequest request = UploadMediaRequest.newBuilder().setName("name3373707").build();
-      ApiFuture<UploadMediaResponse> future =
-          resumableUploadServiceClient.uploadMediaCallable().futureCall(request);
-      // Do something.
-      UploadMediaResponse response = future.get();
-    }
-  }
-}
-// [END localhost7469_v1beta1_generated_ResumableUploadService_UploadMedia_async]
diff --git a/sdk-platform-java/gapic-generator-java/src/main/java/com/google/api/generator/gapic/protoparser/Parser.java b/sdk-platform-java/gapic-generator-java/src/main/java/com/google/api/generator/gapic/protoparser/Parser.java
index efff9219416c..dd7d1689c766 100644
--- a/sdk-platform-java/gapic-generator-java/src/main/java/com/google/api/generator/gapic/protoparser/Parser.java
+++ b/sdk-platform-java/gapic-generator-java/src/main/java/com/google/api/generator/gapic/protoparser/Parser.java
@@ -137,7 +137,8 @@ enum SelectiveGapicType {
           "google.cloud.bigquery.v2.TableService.ListTables");
 
   private static final ImmutableList<Pattern> RESUMABLE_UPLOAD_ALLOWLIST_PATTERNS =
-      ImmutableList.of();
+      ImmutableList.of(
+          Pattern.compile("^google\\.showcase\\.v1beta1\\.ResumableUploadService\\.UploadMedia$"));
 
   // Allow other parsers to access this.
   protected static final SourceCodeInfoParser SOURCE_CODE_INFO_PARSER = new SourceCodeInfoParser();
diff --git a/sdk-platform-java/gapic-generator-java/src/test/java/com/google/api/generator/gapic/protoparser/ParserTest.java b/sdk-platform-java/gapic-generator-java/src/test/java/com/google/api/generator/gapic/protoparser/ParserTest.java
index ff34f675aac9..a1a9bdbcdcd3 100644
--- a/sdk-platform-java/gapic-generator-java/src/test/java/com/google/api/generator/gapic/protoparser/ParserTest.java
+++ b/sdk-platform-java/gapic-generator-java/src/test/java/com/google/api/generator/gapic/protoparser/ParserTest.java
@@ -228,7 +228,7 @@ void parseMethods_resumableUpload() {
     assertEquals(1, methods.size());
     Method uploadMethod = methods.get(0);
     assertEquals("UploadMedia", uploadMethod.name());
-    assertFalse(uploadMethod.isResumableUpload());
+    assertTrue(uploadMethod.isResumableUpload());
   }
 
   @Test