diff --git a/src/devtools/mobileharness/fe/v6/angular/app/core/models/host_action.ts b/src/devtools/mobileharness/fe/v6/angular/app/core/models/host_action.ts
index ec306c2f28..f873a9af08 100644
--- a/src/devtools/mobileharness/fe/v6/angular/app/core/models/host_action.ts
+++ b/src/devtools/mobileharness/fe/v6/angular/app/core/models/host_action.ts
@@ -84,7 +84,12 @@ export declare interface ReleaseReady {
 /**
  * Represents the status of a Lab Server release.
  */
-export type ReleaseStatus = 'Latest' | 'Current' | 'Deprecated' | '';
+export type ReleaseStatus =
+  | 'LATEST'
+  | 'CURRENT'
+  | 'LATEST_AND_CURRENT'
+  | 'VERSION_STATUS_UNSPECIFIED'
+  | '';
 
 /**
  * Configuration for a specific Lab Server release.
@@ -174,7 +179,19 @@ export declare interface DecommissionHostResponse {}
 /**
  * Response for UpdatePassThroughFlags API.
  */
-export declare interface UpdatePassThroughFlagsResponse {}
+export declare interface UpdatePassThroughFlagsResponse {
+  readonly success: boolean;
+  readonly error?: {
+    readonly code:
+      | 'CODE_UNSPECIFIED'
+      | 'PERMISSION_DENIED'
+      | 'INVALID_FLAGS'
+      | 'HOST_NOT_FOUND'
+      | 'WARPGATE_ERROR'
+      | 'UNKNOWN';
+    readonly message?: string;
+  };
+}
 
 /**
  * Response for those rollout action
diff --git a/src/devtools/mobileharness/fe/v6/angular/app/core/services/host/fake_host_service.ts b/src/devtools/mobileharness/fe/v6/angular/app/core/services/host/fake_host_service.ts
index 2ba0d5dfb0..391ee50263 100644
--- a/src/devtools/mobileharness/fe/v6/angular/app/core/services/host/fake_host_service.ts
+++ b/src/devtools/mobileharness/fe/v6/angular/app/core/services/host/fake_host_service.ts
@@ -165,7 +165,7 @@ export class FakeHostService extends HostService {
     const scenario = MOCK_HOST_SCENARIOS.find((s) => s.hostName === hostName);
     if (scenario && scenario.overview) {
       scenario.overview.labServer.passThroughFlags = flags;
-      return of({});
+      return of({success: true});
     } else {
       return throwError(
         () =>
diff --git a/src/devtools/mobileharness/fe/v6/angular/app/core/services/mock_data/hosts/03_shared_mode.ts b/src/devtools/mobileharness/fe/v6/angular/app/core/services/mock_data/hosts/03_shared_mode.ts
index 49f7a935a1..f78c7c6951 100644
--- a/src/devtools/mobileharness/fe/v6/angular/app/core/services/mock_data/hosts/03_shared_mode.ts
+++ b/src/devtools/mobileharness/fe/v6/angular/app/core/services/mock_data/hosts/03_shared_mode.ts
@@ -1,6 +1,7 @@
 /** @fileoverview Mock host scenario in SHARED device config mode. */
 
 import {DeviceConfig} from '../../../models/device_config_models';
+import {PreflightLabServerReleaseResponse} from '../../../models/host_action';
 import {HostConfig} from '../../../models/host_config_models';
 import {MockHostScenario} from '../models';
 import {
@@ -33,6 +34,25 @@ const HOST_CONFIG: HostConfig = {
   },
 };
 
+const PREFLIGHT_RESPONSE: PreflightLabServerReleaseResponse = {
+  ready: {
+    versions: [
+      {
+        name: '[RELEASE] 4.358.0 mobileharness_lab_server',
+        version: '4.358.0',
+        status: 'LATEST_AND_CURRENT',
+        buildTime: new Date(Date.now() - 3600000 * 24).toISOString(),
+      },
+      {
+        name: '[RELEASE] 4.357.0 mobileharness_lab_server',
+        version: '4.357.0',
+        status: '',
+        buildTime: new Date(Date.now() - 3600000 * 48).toISOString(),
+      },
+    ],
+  },
+};
+
 export const SCENARIO_HOST_SHARED_MODE: MockHostScenario = {
   hostName: 'host-shared-mode.example.com',
   scenarioName: '3. Shared Mode',
@@ -44,4 +64,5 @@ export const SCENARIO_HOST_SHARED_MODE: MockHostScenario = {
   },
   defaultDeviceConfig: null, // No default in SHARED mode
   actions: createHostActions('RUNNING', true),
+  releaseResponse: PREFLIGHT_RESPONSE,
 };
diff --git a/src/devtools/mobileharness/fe/v6/angular/app/core/services/mock_data/hosts/ui_status_utils.ts b/src/devtools/mobileharness/fe/v6/angular/app/core/services/mock_data/hosts/ui_status_utils.ts
index d595a27d0a..180e53d987 100644
--- a/src/devtools/mobileharness/fe/v6/angular/app/core/services/mock_data/hosts/ui_status_utils.ts
+++ b/src/devtools/mobileharness/fe/v6/angular/app/core/services/mock_data/hosts/ui_status_utils.ts
@@ -90,7 +90,7 @@ export function createDefaultReleaseResponse(): PreflightLabServerReleaseRespons
         {
           name: 'mobileharness_lab_server',
           version: 'v4.349.0',
-          status: 'Latest',
+          status: 'LATEST',
           buildTime: '2024-03-15 21:30:00',
           ports: [{protocol: 'grpc', portNumber: 9994}],
           releaseDetails: {
@@ -270,7 +270,7 @@ export function createDefaultReleaseResponse(): PreflightLabServerReleaseRespons
         {
           name: 'release_configs',
           version: 'v4.357.0',
-          status: 'Current',
+          status: 'CURRENT',
           buildTime: '2025-03-13 12:00:00',
           ports: [
             {
diff --git a/src/devtools/mobileharness/fe/v6/angular/app/features/host_detail/components/host_overview/flags_dialog/flags_dialog.ng.html b/src/devtools/mobileharness/fe/v6/angular/app/features/host_detail/components/host_overview/flags_dialog/flags_dialog.ng.html
index cdd0aaa2b6..e827a20761 100644
--- a/src/devtools/mobileharness/fe/v6/angular/app/features/host_detail/components/host_overview/flags_dialog/flags_dialog.ng.html
+++ b/src/devtools/mobileharness/fe/v6/angular/app/features/host_detail/components/host_overview/flags_dialog/flags_dialog.ng.html
@@ -4,7 +4,7 @@
   type="host"
   width="64rem"
   height="80vh"
-  maxHeight="90vh"
+  maxHeight="80vh"
   footerType="normal">
   <div header-prefix class="header-icon-wrapper">
     <mat-icon>tune</mat-icon>
@@ -112,7 +112,8 @@
       </div>
 
       <!-- Right Column: Presets -->
-      <div class="flags-dialog-presets-col">
+      <!-- TODO: qiupingf - remove hidden when the RPC is ready. -->
+      <div class="flags-dialog-presets-col hidden">
         <div class="presets-header">
           <div class="header-title">
             <mat-icon>auto_awesome</mat-icon>
@@ -161,9 +162,6 @@ <h3>Quick Presets</h3>
 
   <ng-template #actionsTemplate>
     <div class="footer-actions">
-      @if (errorMessage()) {
-        <span class="error-text">{{ errorMessage() }}</span>
-      }
       <button class="secondary-button" (click)="discardChanges()" [disabled]="!isDirty() || isSaving()">Discard Changes</button>
       <button class="primary-button" (click)="save()" [disabled]="!isDirty() || isSaving()">
         @if (isSaving()) {
diff --git a/src/devtools/mobileharness/fe/v6/angular/app/features/host_detail/components/host_overview/flags_dialog/flags_dialog.scss b/src/devtools/mobileharness/fe/v6/angular/app/features/host_detail/components/host_overview/flags_dialog/flags_dialog.scss
index ed646dd446..e8138f856a 100644
--- a/src/devtools/mobileharness/fe/v6/angular/app/features/host_detail/components/host_overview/flags_dialog/flags_dialog.scss
+++ b/src/devtools/mobileharness/fe/v6/angular/app/features/host_detail/components/host_overview/flags_dialog/flags_dialog.scss
@@ -507,6 +507,10 @@
         }
       }
     }
+
+    &.hidden {
+      display: none;
+    }
   }
 }
 
diff --git a/src/devtools/mobileharness/fe/v6/angular/app/features/host_detail/components/host_overview/flags_dialog/flags_dialog.ts b/src/devtools/mobileharness/fe/v6/angular/app/features/host_detail/components/host_overview/flags_dialog/flags_dialog.ts
index 9ae58b97f1..2f64b4f11b 100644
--- a/src/devtools/mobileharness/fe/v6/angular/app/features/host_detail/components/host_overview/flags_dialog/flags_dialog.ts
+++ b/src/devtools/mobileharness/fe/v6/angular/app/features/host_detail/components/host_overview/flags_dialog/flags_dialog.ts
@@ -21,7 +21,11 @@ import {MatInputModule} from '@angular/material/input';
 import {MatProgressSpinnerModule} from '@angular/material/progress-spinner';
 import {take} from 'rxjs/operators';
 
-import {PopularFlag} from '../../../../../core/models/host_action';
+import {SnackBarService} from '@deviceinfra/app/shared/services/snackbar_service';
+import {
+  PopularFlag,
+  UpdatePassThroughFlagsResponse,
+} from '../../../../../core/models/host_action';
 import {HOST_SERVICE} from '../../../../../core/services/host/host_service';
 import {Dialog} from '../../../../../shared/components/config_common/dialog/dialog';
 
@@ -58,6 +62,7 @@ export class FlagsDialog implements OnInit {
   readonly data = inject<FlagsDialogData>(MAT_DIALOG_DATA);
   private readonly dialogRef = inject(MatDialogRef<FlagsDialog>);
   private readonly hostService = inject(HOST_SERVICE);
+  private readonly snackBarService = inject(SnackBarService);
 
   readonly isListMode = signal(true);
   readonly currentFlagsArray = signal<string[]>([]);
@@ -65,7 +70,6 @@ export class FlagsDialog implements OnInit {
   readonly presets = signal<PopularFlag[]>([]);
   readonly isLoadingPresets = signal(false);
   readonly isSaving = signal(false);
-  readonly errorMessage = signal('');
   readonly addInput = signal('');
   readonly filterText = signal('');
   readonly rawTextFlags = signal('');
@@ -196,13 +200,23 @@ export class FlagsDialog implements OnInit {
   }
 
   appendPreset(preset: PopularFlag) {
+    const newFlags = this.splitFlags(preset.cmd);
     if (this.isListMode()) {
-      const newFlags = this.splitFlags(preset.cmd);
-      this.currentFlagsArray.update((flags) => [...flags, ...newFlags]);
+      this.currentFlagsArray.update((flags) => {
+        const currentSet = new Set(flags);
+        const flagsToAppend = newFlags.filter((f) => !currentSet.has(f));
+        return [...flags, ...flagsToAppend];
+      });
     } else {
       this.rawTextFlags.update((text) => {
+        const currentFlags = this.splitFlags(text);
+        const currentSet = new Set(currentFlags);
+        const flagsToAppend = newFlags.filter((f) => !currentSet.has(f));
+        if (flagsToAppend.length === 0) return text;
         const trimmed = text.trim();
-        return trimmed ? `${trimmed} ${preset.cmd}` : preset.cmd;
+        return trimmed
+          ? `${trimmed} ${flagsToAppend.join(' ')}`
+          : flagsToAppend.join(' ');
       });
     }
   }
@@ -228,19 +242,27 @@ export class FlagsDialog implements OnInit {
     }
 
     this.isSaving.set(true);
-    this.errorMessage.set('');
 
     this.hostService
       .updatePassThroughFlags(this.data.hostName, finalString)
       .pipe(take(1))
       .subscribe({
-        next: () => {
-          this.isSaving.set(false);
-          this.dialogRef.close(finalString);
+        next: (response: UpdatePassThroughFlagsResponse) => {
+          if (response.success) {
+            this.isSaving.set(false);
+            this.dialogRef.close(finalString);
+          } else {
+            this.isSaving.set(false);
+            const msg =
+              response.error?.message ||
+              response.error?.code ||
+              'Failed to save flags';
+            this.snackBarService.showError(msg);
+          }
         },
-        error: (err: Error) => {
+        error: () => {
           this.isSaving.set(false);
-          this.errorMessage.set(err.message || 'Failed to save flags');
+          this.snackBarService.showError('Failed to save flags');
         },
       });
   }
diff --git a/src/devtools/mobileharness/fe/v6/angular/app/features/host_detail/components/host_overview/release_dialog/release_dialog.ng.html b/src/devtools/mobileharness/fe/v6/angular/app/features/host_detail/components/host_overview/release_dialog/release_dialog.ng.html
index 1464d81e9e..41914b46fb 100644
--- a/src/devtools/mobileharness/fe/v6/angular/app/features/host_detail/components/host_overview/release_dialog/release_dialog.ng.html
+++ b/src/devtools/mobileharness/fe/v6/angular/app/features/host_detail/components/host_overview/release_dialog/release_dialog.ng.html
@@ -3,221 +3,187 @@
   subtitle="Host: {{ data.hostName }}"
   type="host"
   width="72rem"
-  height="750px"
   maxHeight="90vh"
   footerType="normal">
   <mat-dialog-content class="dialog-content">
     @if (currentStep() === 1) {
-      <!-- Step 1: Version Selection -->
-      <div class="step-1-container">
-        <div class="info-alert">
-          <mat-icon>
-            info_outline
-          </mat-icon>
-          <span>
-            Select a release candidate to proceed.
-          </span>
-        </div>
-        <div class="content-splitter">
-          <div class="versions-panel">
-            <table mat-table [dataSource]="availableVersions" class="versions-table">
-              <!-- Version Column -->
-              <ng-container matColumnDef="version">
-                <th mat-header-cell *matHeaderCellDef>
-                  Version
-                </th>
-                <td mat-cell *matCellDef="let element">
-                  <div class="version-label">
-                    {{ element.version }}
-                  </div>
-                  <div class="version-name">
-                    {{ element.name }}
-                  </div>
-                </td>
-              </ng-container>
-              <!-- Build Date Column -->
-              <ng-container matColumnDef="buildTime">
-                <th mat-header-cell *matHeaderCellDef>
-                  Build Date
-                </th>
-                <td mat-cell *matCellDef="let element">
-                  {{ element.buildTime | date:'shortDate' }}
-                </td>
-              </ng-container>
-              <!-- Status Column -->
-              <ng-container matColumnDef="status">
-                <th mat-header-cell *matHeaderCellDef>
-                  Status
-                </th>
-                <td mat-cell *matCellDef="let element">
-                  @if (element.status?.toLowerCase() === 'latest') {
-                    <span class="status-badge latest">
-                      Latest
+      <div class="info-alert">
+        <mat-icon>
+          info_outline
+        </mat-icon>
+        <span>
+          Select a release candidate to proceed.
+        </span>
+      </div>
+      <div class="content-splitter">
+        <div class="versions-panel">
+          @for(version of formattedAvailableVersions(); track version.version) {
+            <div class="version-card"
+                [class.selected]="selectedVersion()?.version === version.version"
+                (click)="selectVersion(version)">
+              <div class="version-info">
+                <div class="version-header">
+                  <span class="version-number">{{version.version}}</span>
+                  @if(version.status === 'CURRENT' || version.status === 'LATEST_AND_CURRENT') {
+                    <span class="status-pill current-version">
+                      <mat-icon>check</mat-icon>Current Version
                     </span>
                   }
-                  @if (element.status?.toLowerCase() === 'current') {
-                    <span class="status-badge current">
-                      Current
-                    </span>
+                  @if(version.status === 'LATEST' || version.status === 'LATEST_AND_CURRENT') {
+                    <span class="status-pill latest-stable">Latest Stable</span>
                   }
-                </td>
-              </ng-container>
-              <!-- Actions Column -->
-              <ng-container matColumnDef="actions">
-                <th mat-header-cell *matHeaderCellDef></th>
-                <td mat-cell *matCellDef="let element" class="row-actions">
-                  <button mat-icon-button title="View Details" (click)="viewDetails(element); $event.stopPropagation();">
-                    <mat-icon style="opacity: 1;">
-                      info
-                    </mat-icon>
-                  </button>
-                </td>
-              </ng-container>
-              <tr mat-header-row *matHeaderRowDef="displayedColumns"></tr>
-              <tr mat-row *matRowDef="let row; columns: displayedColumns;" class="version-row" [class.selected]="selectedVersion()?.version === row.version" (click)="selectVersion(row)">
-              </tr>
-            </table>
-          </div>
-          <!-- Manifest Side Panel -->
-          <div class="manifest-panel" [class.open]="showDetails()">
-            <div class="manifest-header">
-              <span>
-                Build Manifest
-              </span>
-              <button mat-icon-button (click)="showDetails.set(false)" title="Close Panel">
-                <mat-icon>close</mat-icon>
-              </button>
-            </div>
-            <div class="manifest-tabs">
-              <button class="tab-btn" [class.active]="currentTab() === 'metadata'" (click)="switchTab('metadata')">
-                Metadata
-              </button>
-              <button class="tab-btn" [class.active]="currentTab() === 'files'" (click)="switchTab('files')">
-                Files
-              </button>
-              <button class="tab-btn" [class.active]="currentTab() === 'commands'" (click)="switchTab('commands')">
-                Commands
-              </button>
+                </div>
+                <div class="version-name-card">
+                  {{version.name || 'Available release candidate package binary.'}}
+                </div>
+              </div>
+              <div class="version-actions">
+                <button mat-icon-button title="View Details" (click)="viewDetails(version); $event.stopPropagation();">
+                  <mat-icon>info</mat-icon>
+                </button>
+              </div>
             </div>
-            <div class="manifest-content">
-              @if (currentTab() === 'metadata') {
-                <div class="metadata-content">
-                  <div class="detail-item">
-                    <mat-icon>tag</mat-icon>
-                    <div>
-                      <div class="label">Version</div>
-                      <div class="value">
-                        {{ selectedVersion()?.version || 'N/A' }}
-                      </div>
+          }
+        </div>
+        <!-- Manifest Side Panel -->
+        <div class="manifest-panel" [class.open]="showDetails()">
+          <div class="manifest-header">
+            <span>
+              Build Manifest
+            </span>
+            <button mat-icon-button (click)="showDetails.set(false)" title="Close Panel">
+              <mat-icon>close</mat-icon>
+            </button>
+          </div>
+          <div class="manifest-tabs">
+            <button class="tab-btn" [class.active]="currentTab() === 'metadata'" (click)="switchTab('metadata')">
+              Metadata
+            </button>
+            <button class="tab-btn" [class.active]="currentTab() === 'files'" (click)="switchTab('files')">
+              Files
+            </button>
+            <button class="tab-btn" [class.active]="currentTab() === 'commands'" (click)="switchTab('commands')">
+              Commands
+            </button>
+          </div>
+          <div class="manifest-content">
+            @if (currentTab() === 'metadata') {
+              <div class="metadata-content">
+                <div class="detail-item">
+                  <mat-icon>tag</mat-icon>
+                  <div>
+                    <div class="label">Version</div>
+                    <div class="value">
+                      {{ selectedVersion()?.version || 'N/A' }}
                     </div>
                   </div>
-                  <div class="detail-item">
-                    <mat-icon>label</mat-icon>
-                    <div>
-                      <div class="label">Release Name</div>
-                      <div class="value">
-                        {{ selectedVersion()?.name || 'N/A' }}
-                      </div>
+                </div>
+                <div class="detail-item">
+                  <mat-icon>label</mat-icon>
+                  <div>
+                    <div class="label">Release Name</div>
+                    <div class="value">
+                      {{ selectedVersion()?.name || 'N/A' }}
                     </div>
                   </div>
-                  <div class="detail-item">
-                    <mat-icon>schedule</mat-icon>
-                    <div>
-                      <div class="label">Build Time</div>
-                      <div class="value">
-                        {{ selectedVersion()?.buildTime | date:'medium' }}
-                      </div>
+                </div>
+                <div class="detail-item">
+                  <mat-icon>schedule</mat-icon>
+                  <div>
+                    <div class="label">Status</div>
+                    <div class="value">
+                      {{ statusDisplayMap[selectedVersion()?.status || ''] || selectedVersion()?.status || 'N/A' }}
                     </div>
                   </div>
-                  <div class="detail-item">
-                    <mat-icon>settings_ethernet</mat-icon>
-                    <div>
-                      <div class="label">Ports</div>
-                      <div class="value">
-                        @for (p of selectedVersion()?.ports; track p.portNumber; let last = $last) {
-                          {{ p.protocol }}:{{ p.portNumber }}{{ last ? '' : ', ' }}
-                        }
-                        @empty { N/A }
-                      </div>
+                </div>
+                <div class="detail-item">
+                  <mat-icon>settings_ethernet</mat-icon>
+                  <div>
+                    <div class="label">Ports</div>
+                    <div class="value">
+                      @for (p of selectedVersion()?.ports; track p.portNumber; let last = $last) {
+                        {{ p.protocol }}:{{ p.portNumber }}{{ last ? '' : ', ' }}
+                      }
+                      @empty { N/A }
                     </div>
                   </div>
-                  @defer (on idle) {
-                    @for (group of selectedVersion()?.releaseDetails?.changeLogs; track group.name) {
-                      <div class="changelist-section">
-                        <div class="section-title">{{ group.name }}</div>
-                        <ul>
-                          @for (c of group.items; track c) {
-                            @if (c.change) {
-                              <li>
-                                <span class="cl-number">cl/{{ c.change.cl }}</span>: {{ c.change.text }}
-                                @if (c.change.bugs && c.change.bugs.length > 0) {
-                                  <span class="bug-number">
-                                    (b/{{ c.change.bugs.join(', ') }})
-                                  </span>
-                                }
-                              </li>
-                            }
-                            @if (c.bug) {
-                              <li>
-                                <span class="cl-number">b/{{ c.bug.bug }}</span>: {{ c.bug.text }}
-                              </li>
-                            }
-                          }
-                        </ul>
-                      </div>
-                    }
-                  } @placeholder {
-                    <div class="empty-text">
-                      Loading change logs...
-                    </div>
-                  }
                 </div>
-              }
-              @if (currentTab() === 'files') {
-                <div class="files-content">
-                  @defer (on idle) {
-                    @for (file of selectedVersion()?.releaseDetails?.files; track file.name) {
-                      <div class="file-item">
-                        <div class="file-key">{{ file.name }}</div>
-                        @if (file.path) {
-                          <div class="file-value">{{ file.path }}</div>
-                        } @else {
-                          <div class="file-value not-set">Not set</div>
+                @defer (on idle) {
+                  @for (group of selectedVersion()?.releaseDetails?.changeLogs; track group.name) {
+                    <div class="changelist-section">
+                      <div class="section-title">{{ group.name }}</div>
+                      <ul>
+                        @for (c of group.items; track c) {
+                          @if (c.change) {
+                            <li>
+                              <span class="cl-number">cl/{{ c.change.cl }}</span>: {{ c.change.text }}
+                              @if (c.change.bugs && c.change.bugs.length > 0) {
+                                <span class="bug-number">
+                                  (b/{{ c.change.bugs.join(', ') }})
+                                </span>
+                              }
+                            </li>
+                          }
+                          @if (c.bug) {
+                            <li>
+                              <span class="cl-number">b/{{ c.bug.bug }}</span>: {{ c.bug.text }}
+                            </li>
+                          }
                         }
-                      </div>
-                    } @empty {
-                      <div class="empty-text"> No Files </div>
-                    }
-                  } @placeholder {
-                    <div class="empty-text">
-                      Loading files...
+                      </ul>
                     </div>
                   }
-                </div>
-              }
-              @if (currentTab() === 'commands') {
-                <div class="commands-content">
-                  @if (hasCommands()) {
-                    @if (hasSyncCommands()) {
-                      <div class="section-title">Sync Commands</div>
-                      @for (cmd of selectedVersion()?.releaseDetails?.syncCommands; track cmd.name) {
-                        <span class="command-name">{{ cmd.name }}</span>
-                        <code class="command-block">{{ cmd.command }}</code>
+                } @placeholder {
+                  <div class="empty-text">
+                    Loading change logs...
+                  </div>
+                }
+              </div>
+            }
+            @if (currentTab() === 'files') {
+              <div class="files-content">
+                @defer (on idle) {
+                  @for (file of selectedVersion()?.releaseDetails?.files; track file.name) {
+                    <div class="file-item">
+                      <div class="file-key">{{ file.name }}</div>
+                      @if (file.path) {
+                        <div class="file-value">{{ file.path }}</div>
+                      } @else {
+                        <div class="file-value not-set">Not set</div>
                       }
+                    </div>
+                  } @empty {
+                    <div class="empty-text"> No Files </div>
+                  }
+                } @placeholder {
+                  <div class="empty-text">
+                    Loading files...
+                  </div>
+                }
+              </div>
+            }
+            @if (currentTab() === 'commands') {
+              <div class="commands-content">
+                @if (hasCommands()) {
+                  @if (hasSyncCommands()) {
+                    <div class="section-title">Sync Commands</div>
+                    @for (cmd of selectedVersion()?.releaseDetails?.syncCommands; track cmd.name) {
+                      <span class="command-name">{{ cmd.name }}</span>
+                      <code class="command-block">{{ cmd.command }}</code>
                     }
-                    @if (hasAsyncCommands()) {
-                      <div class="section-title">Async Commands</div>
-                      @for (cmd of selectedVersion()?.releaseDetails?.asyncCommands; track cmd.name) {
-                        <span class="command-name">{{ cmd.name }}</span>
-                        <code class="command-block async">{{ cmd.command }}</code>
-                      }
+                  }
+                  @if (hasAsyncCommands()) {
+                    <div class="section-title">Async Commands</div>
+                    @for (cmd of selectedVersion()?.releaseDetails?.asyncCommands; track cmd.name) {
+                      <span class="command-name">{{ cmd.name }}</span>
+                      <code class="command-block async">{{ cmd.command }}</code>
                     }
-                  } @else {
-                    <div class="empty-text"> No Commands </div>
                   }
-                </div>
-              }
-            </div>
+                } @else {
+                  <div class="empty-text"> No Commands </div>
+                }
+              </div>
+            }
           </div>
         </div>
       </div>
@@ -225,28 +191,39 @@
       <!-- Step 2: Deployment Confirmation -->
       <div class="step-2-container">
         <header class="step-2-header">
-          <div class="header-icon"><mat-icon>rocket_launch</mat-icon></div>
+          <div class="header-icon" [attr.data-delta-type]="versionDeltaInfo().type">
+            <mat-icon>rocket_launch</mat-icon>
+          </div>
           <div>
             <h3>Ready to Deploy</h3>
             <p>Please review your deployment configuration before proceeding.</p>
           </div>
         </header>
-        <div class="version-summary-card">
+        <div class="version-summary-card" [attr.data-delta-type]="versionDeltaInfo().type">
           <div class="left-section">
-            <div class="icon-bg"><mat-icon>label</mat-icon></div>
+            <div class="icon-bg">
+              <mat-icon>{{versionDeltaInfo().icon}}</mat-icon>
+            </div>
             <div class="version-details">
-              <div class="label">Selected Version</div>
+              <div class="label">Selected Release Target</div>
               <div class="value">
                 <span class="version-str">{{ selectedVersion()?.version }}</span>
-                @if (selectedVersion()?.status?.toLowerCase() === 'latest') {
+                @if (selectedVersion()?.status === 'LATEST_AND_CURRENT') {
+                  <span class="status-badge current">Current</span>
+                  <span class="status-badge latest">Latest</span>
+                } @else if (selectedVersion()?.status === 'LATEST') {
                   <span class="status-badge latest">Latest</span>
+                } @else if (selectedVersion()?.status === 'CURRENT') {
+                  <span class="status-badge current">Current</span>
                 }
               </div>
             </div>
           </div>
           <div class="right-section">
-            <div class="label">Build Date</div>
-            <div class="value">{{ selectedVersion()?.buildTime | date:'mediumDate' }}</div>
+            <span class="delta-pill">
+              <mat-icon>{{versionDeltaInfo().icon}}</mat-icon>
+              {{versionDeltaInfo().label}}
+            </span>
           </div>
         </div>
         <div class="flags-section">
diff --git a/src/devtools/mobileharness/fe/v6/angular/app/features/host_detail/components/host_overview/release_dialog/release_dialog.scss b/src/devtools/mobileharness/fe/v6/angular/app/features/host_detail/components/host_overview/release_dialog/release_dialog.scss
index 38f52d49e2..b5c54f3b77 100644
--- a/src/devtools/mobileharness/fe/v6/angular/app/features/host_detail/components/host_overview/release_dialog/release_dialog.scss
+++ b/src/devtools/mobileharness/fe/v6/angular/app/features/host_detail/components/host_overview/release_dialog/release_dialog.scss
@@ -1,19 +1,15 @@
 @use '@angular/material' as mat;
-@use  '../../../../../shared/styles/common.scss' as common;
+@use '../../../../../shared/styles/common.scss' as common;
 @use '../../../../../shared/styles/typography.scss' as typography;
 
-:host {
-  @include mat.table-overrides((
-    header-container-height: 3rem,
-  ));
-}
-
 .dialog-content {
-  @include common.shared-scrollbar-style();
-  flex-grow: 1;
-  overflow-y: auto;
   padding: 1.5rem;
-  background-color: #f8fafc;
+  overflow: hidden;
+  flex-direction: column;
+  flex-grow: 1;
+  display: flex;
+  max-height: 48vh;
+  height: 48vh;
 }
 
 .info-alert {
@@ -26,6 +22,7 @@
   border-radius: 0.5rem;
   border: 1px solid #dbeafe;
   margin-bottom: 1rem;
+  letter-spacing: normal;
 
   span {
     font-weight: 500;
@@ -35,140 +32,161 @@
 }
 
 .content-splitter {
-  display: flex;
   align-items: stretch;
+  display: flex;
+  flex-grow: 1;
   overflow: hidden;
-  height: 500px;
+  height: 48vh;
 }
 
 .versions-panel {
-  flex-grow: 1;
+  @include common.shared-scrollbar-style();
+  padding: 1rem;
+  background-color: #f1f5f999;
+  border-radius: 1rem;
+  border: 1px solid #e5e7eb99;
   overflow-y: auto;
-  border: 1px solid #e2e8f0;
-  border-radius: 0.75rem;
-  background-color: white;
-  box-shadow: 0 1px 2px rgba(0, 0, 0, 0.05);
+  user-select: none;
+  flex-grow: 1;
+  gap: 0.875rem;
+  display: flex;
+  flex-direction: column;
 
-  .versions-table {
-    width: 100%;
-    border-collapse: collapse;
-    text-align: left;
+  .version-card {
+    transition-duration: 200ms;
+    transition-property: all;
+    transition-timing-function: cubic-bezier(0.4, 0, 0.2, 1);
+    padding: 1rem 1.25rem;
+    border: 1px solid #e2e8f0b3;
+    border-radius: 0.75rem;
+    box-shadow: 0 1px 2px rgba(0, 0, 0, 0.05);
+    display: flex;
+    align-items: center;
+    justify-content: space-between;
+    cursor: pointer;
+    background-color: white;
 
-    th {
-      background-color: #f8fafc;
-      padding: 0.75rem 1rem;
-      font-size: 0.75rem;
-      font-weight: 600;
-      color: #64748b;
-      border-bottom: 1px solid #e2e8f0;
-      position: sticky;
-      top: 0;
-      z-index: 10;
+    &:hover {
+      box-shadow: 0 4px 6px -1px rgba(0,0,0,0.1), 0 2px 4px -2px rgba(0,0,0,0.1);
+      border-color: #93c5fd4d;
+      transform: translateY(-2px);
     }
 
-    td {
-      padding: 0.75rem 1rem;
-      border-bottom: 1px solid #f1f5f9;
-      font-size: 0.875rem;
+    &.selected {
+      border: 2px solid #2563eb;
+      background: linear-gradient(to right, #eff6ff66, #eff6ff1a);
+      box-shadow: 0 4px 6px -1px rgba(59,130,246,0.1), 0 2px 4px -2px rgba(59,130,246,0.1);
     }
 
-    .version-row {
-      cursor: pointer;
-      transition: background-color 0.2s;
-
-      &:hover {
-        background-color: #f8fafc;
-      }
-
-      &.selected {
-        background-color: #eff6ff;
+    .version-info {
+      min-width: 0;
+      display: flex;
+      flex-direction: column;
+      gap: 0.25rem;
+    }
 
-        .version-label {
-          color: #1e40af;
-        }
-      }
+    .version-header {
+      display: flex;
+      align-items: center;
+      gap: 0.5rem;
+      flex-wrap: wrap;
     }
 
-    .version-label {
+    .version-number {
+      font-family: monospace;
+      font-size: 0.875rem;
       font-weight: 700;
       color: #0f172a;
+      letter-spacing: normal;
     }
 
-    .version-name {
-      font-size: 0.75rem;
-      color: #94a3b8;
-      margin-top: 0.125rem;
-    }
-
-    .status-badge {
-      font-size: 0.75rem;
-      font-weight: 700;
+    .status-pill {
       padding: 0.125rem 0.5rem;
       border-radius: 9999px;
-      border: 1px solid transparent;
+      font-size: 0.5625rem;
+      font-weight: 700;
+      box-shadow: 0 1px 2px rgba(0,0,0,0.05);
+      border: 1px solid;
+      display: inline-flex;
+      align-items: center;
+      gap: 0.125rem;
+      line-height: 0.75rem;
+      letter-spacing: normal;
 
-      &.latest {
+      mat-icon {
+        font-size: 0.625rem;
+        height: 0.625rem;
+        width: 0.625rem;
+      }
+
+      &.current-version {
+        background-color: #2563eb;
+        color: white;
+        border-color: #2563eb;
+      }
+
+      &.latest-stable {
         background-color: #dcfce7;
-        color: #15803d;
+        color: #166534;
         border-color: #bbf7d0;
       }
+    }
 
-      &.current {
-        background-color: #dbeafe;
-        color: #1d4ed8;
-        border-color: #bfdbfe;
-      }
+    .version-name-card {
+      font-size: 0.6875rem;
+      color: #94a3b8;
+      line-height: 1.1;
     }
 
-    .row-actions {
+    .version-actions {
       display: flex;
-      justify-content: flex-end;
       align-items: center;
       gap: 0.5rem;
+      margin-left: 1rem;
+      flex-shrink: 0;
 
-      button[mat-icon-button] {
-        color: #2563eb;
-        opacity: 1;
-      }
-
-      button[mat-flat-button] {
-        background-color: #2563eb;
-        color: white;
+      button {
+        color: #94a3b8;
+        &:hover {
+          color: #2563eb;
+          background-color: #eff6ffcc;
+        }
       }
     }
   }
 }
 
 .manifest-panel {
-  width: 0;
-  opacity: 0;
-  border: 1px solid #e2e8f0;
-  border-radius: 0.75rem;
+  transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
   background-color: white;
-  display: flex;
-  flex-direction: column;
+  border: 1px solid #e5e7eb;
+  border-radius: .75rem;
   overflow: hidden;
-  transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
-  letter-spacing: normal;
+  flex-direction: column;
+  display: flex;
+  width: 0;
+  opacity: 0;
 
   &.open {
     transform: translateX(0);
-    width: 400px;
+    width: 350px;
     margin-left: 1rem;
     opacity: 1;
   }
 
   .manifest-header {
     padding: 0 0 0 1rem;
-    background-color: #f8fafc;
-    border-bottom: 1px solid #e2e8f0;
+    background-color: #f9fafb;
+    border-bottom: 1px solid #f3f4f6;
     display: flex;
     justify-content: space-between;
     align-items: center;
+    color: #374151;
     font-size: 0.75rem;
     font-weight: 700;
-    color: #334155;
+    line-height: 1rem;
     flex-shrink: 0;
+    letter-spacing: normal;
   }
 
   .manifest-tabs {
@@ -201,6 +219,7 @@
   }
 
   .manifest-content {
+    @include common.shared-scrollbar-style();
     flex-grow: 1;
     overflow-y: auto;
     padding: 1rem;
@@ -214,13 +233,15 @@
     .detail-item {
       display: flex;
       gap: 0.75rem;
-      align-items: flex-start;
+      align-items: center;
+      letter-spacing: normal;
+      line-height: 1.25rem;
 
       mat-icon {
         color: #2563eb;
-        font-size: 1.25rem;
-        width: 1.25rem;
-        height: 1.25rem;
+        font-size: 1rem;
+        width: 1rem;
+        height: 1rem;
       }
 
       .label {
@@ -406,6 +427,49 @@
   margin-bottom: 2rem;
   box-shadow: 0 1px 2px rgba(0, 0, 0, 0.05);
 
+  &[data-delta-type='upgrade'] {
+    .icon-bg {
+      background-color: #ecfdf5;
+      color: #059669;
+      border-color: #d1fae599;
+    }
+    .delta-pill {
+      background-color: #ecfdf5;
+      color: #059669;
+    }
+  }
+  &[data-delta-type='downgrade'] {
+    .icon-bg {
+      background-color: #fff1f2;
+      color: #e11d48;
+      border-color: #ffe4e699;
+    }
+    .delta-pill {
+      background-color: #fff1f2;
+      color: #e11d48;
+    }
+  }
+  &[data-delta-type='redeploy'] {
+    .icon-bg {
+      background-color: #eff6ff;
+      color: #1d4ed8;
+    }
+    .delta-pill {
+      background-color: #eff6ff;
+      color: #1d4ed8;
+    }
+  }
+  &[data-delta-type='deploy'] {
+    .icon-bg {
+      background-color: #eff6ff;
+      color: #2563eb;
+    }
+    .delta-pill {
+      background-color: #eff6ff;
+      color: #2563eb;
+    }
+  }
+
   .left-section {
     display: flex;
     gap: 1rem;
@@ -413,10 +477,10 @@
   }
 
   .icon-bg {
-    width: 2.5rem;
-    height: 2.5rem;
-    background-color: #f1f5f9;
-    color: #94a3b8;
+    width: 3rem;
+    height: 3rem;
+    background-color: #eff6ff;
+    color: #2563eb;
     border-radius: 0.5rem;
     display: flex;
     align-items: center;
@@ -428,6 +492,7 @@
     font-weight: 700;
     color: #9ca3af;
     letter-spacing: normal;
+    text-transform: uppercase;
   }
 
   .value {
@@ -438,20 +503,51 @@
 
     .version-str {
       font-size: 1.25rem;
-      font-family: monospace;
       font-weight: 700;
       color: #0f172a;
     }
+
+    .status-badge {
+      padding: 0.125rem 0.375rem;
+      border-radius: 0.25rem;
+      font-weight: 700;
+      font-size: 9px;
+      line-height: normal;
+
+      &.current {
+        background-color: #eff6ff;
+        color: #2563eb;
+        border: 1px solid #dbeafe;
+      }
+
+      &.latest {
+        background-color: #f0fdf4;
+        color: #16a34a;
+        border: 1px solid #dcfce7;
+      }
+    }
   }
 
   .right-section {
     text-align: right;
+  }
+
+  .delta-pill {
+    font-size: 0.625rem;
+    font-weight: 700;
+    text-transform: uppercase;
+    letter-spacing: 0.05em;
+    padding: 0.25rem 0.75rem;
+    border-radius: 9999px;
+    display: flex;
+    align-items: center;
+    gap: 0.25rem;
+    line-height: 1rem;
 
-    .value {
-      justify-content: flex-end;
+    mat-icon {
       font-size: 0.875rem;
-      font-weight: 600;
-      color: #475569;
+      height: 0.875rem;
+      width: 0.875rem;
     }
   }
 }
diff --git a/src/devtools/mobileharness/fe/v6/angular/app/features/host_detail/components/host_overview/release_dialog/release_dialog.ts b/src/devtools/mobileharness/fe/v6/angular/app/features/host_detail/components/host_overview/release_dialog/release_dialog.ts
index 8dce7eae8b..f97a1cfcd5 100644
--- a/src/devtools/mobileharness/fe/v6/angular/app/features/host_detail/components/host_overview/release_dialog/release_dialog.ts
+++ b/src/devtools/mobileharness/fe/v6/angular/app/features/host_detail/components/host_overview/release_dialog/release_dialog.ts
@@ -19,13 +19,18 @@ import {MatFormFieldModule} from '@angular/material/form-field';
 import {MatIconModule} from '@angular/material/icon';
 import {MatInputModule} from '@angular/material/input';
 import {MatProgressSpinnerModule} from '@angular/material/progress-spinner';
-import {MatTableModule} from '@angular/material/table';
 
 import {DeployableVersion} from '@deviceinfra/app/core/models/host_action';
 import {FlagsDialog} from '@deviceinfra/app/features/host_detail/components/host_overview/flags_dialog/flags_dialog';
 import {Dialog} from '@deviceinfra/app/shared/components/config_common/dialog/dialog';
 import {SnackBarService} from '@deviceinfra/app/shared/services/snackbar_service';
 
+interface VersionDelta {
+  type: 'deploy' | 'upgrade' | 'downgrade' | 'redeploy';
+  label: 'Deploy' | 'Upgrade' | 'Downgrade' | 'Redeploy';
+  icon: 'rocket_launch' | 'arrow_upward' | 'arrow_downward' | 'refresh';
+}
+
 /**
  * Data passed to the ReleaseDialog component.
  */
@@ -46,7 +51,6 @@ export interface ReleaseDialogData {
   changeDetection: ChangeDetectionStrategy.OnPush,
   imports: [
     Dialog,
-    MatTableModule,
     CommonModule,
     FormsModule,
     MatDialogModule,
@@ -62,10 +66,22 @@ export class ReleaseDialog implements OnInit {
   private readonly snackBar = inject(SnackBarService);
   private readonly dialog = inject(MatDialog);
 
-  displayedColumns: string[] = ['version', 'buildTime', 'status', 'actions'];
-
   readonly currentStep = signal<number>(1);
   readonly selectedVersion = signal<DeployableVersion | null>(null);
+  readonly availableVersions = signal<DeployableVersion[]>([]);
+
+  readonly formattedAvailableVersions = computed(() => {
+    return this.availableVersions().map((v) => ({
+      ...v,
+      version: `v${v.version.replace(/^v/, '')}`,
+    }));
+  });
+
+  readonly statusDisplayMap: Record<string, string> = {
+    'LATEST': 'Latest',
+    'CURRENT': 'Current',
+    'LATEST_AND_CURRENT': 'Latest and Current',
+  };
 
   readonly hasSyncCommands = computed(() => {
     return !!this.selectedVersion()?.releaseDetails?.syncCommands?.length;
@@ -78,17 +94,77 @@ export class ReleaseDialog implements OnInit {
   readonly hasCommands = computed(() => {
     return this.hasSyncCommands() || this.hasAsyncCommands();
   });
+
+  readonly versionDeltaInfo = computed<VersionDelta>(() => {
+    const target = this.selectedVersion()?.version || '';
+    const current =
+      this.formattedAvailableVersions().find(
+        (v) => v.status === 'CURRENT' || v.status === 'LATEST_AND_CURRENT',
+      )?.version || '';
+
+    const defaultResult: VersionDelta = {
+      type: 'deploy',
+      label: 'Deploy',
+      icon: 'rocket_launch',
+    };
+
+    if (!target || !current || current === 'Unknown' || current === 'N/A') {
+      return defaultResult;
+    }
+
+    const s1 = target.replace(/^v/i, '').split('.');
+    const s2 = current.replace(/^v/i, '').split('.');
+
+    let type: 'upgrade' | 'downgrade' | 'redeploy' = 'redeploy';
+
+    for (let i = 0; i < Math.max(s1.length, s2.length); i++) {
+      const seg1 = s1[i] ?? '0';
+      const seg2 = s2[i] ?? '0';
+
+      if (seg1 === seg2) continue;
+
+      const n1 = Number(seg1);
+      const n2 = Number(seg2);
+
+      if (!isNaN(n1) && !isNaN(n2)) {
+        // Both are numbers, compare numerically
+        type = n1 > n2 ? 'upgrade' : 'downgrade';
+        break;
+      } else {
+        // One or both are non-numeric. Compare lexicographically.
+        type = seg1 > seg2 ? 'upgrade' : 'downgrade';
+        break;
+      }
+    }
+
+    const deltaConfig: Record<
+      'upgrade' | 'downgrade' | 'redeploy',
+      Omit<VersionDelta, 'type'>
+    > = {
+      'upgrade': {label: 'Upgrade', icon: 'arrow_upward'},
+      'downgrade': {label: 'Downgrade', icon: 'arrow_downward'},
+      'redeploy': {label: 'Redeploy', icon: 'refresh'},
+    };
+
+    return {
+      type,
+      ...deltaConfig[type],
+    };
+  });
+
   readonly currentTab = signal<string>('metadata');
   readonly tempFlags = signal<string>('');
   readonly flagsModifiedThisSession = signal<boolean>(false);
   readonly showDetails = signal<boolean>(false);
   readonly isDeploying = signal<boolean>(false);
 
-  availableVersions: DeployableVersion[] = [];
-
   ngOnInit() {
-    this.availableVersions = this.data.releaseConfigs || [];
     this.tempFlags.set(this.data.passThroughFlags());
+    this.processVersions(this.data.releaseConfigs || []);
+  }
+
+  processVersions(versions: DeployableVersion[]) {
+    this.availableVersions.set(versions);
   }
 
   selectVersion(version: DeployableVersion) {
diff --git a/src/devtools/mobileharness/fe/v6/service/proto/host/host_resources.proto b/src/devtools/mobileharness/fe/v6/service/proto/host/host_resources.proto
index a45251b08a..adba309aaf 100644
--- a/src/devtools/mobileharness/fe/v6/service/proto/host/host_resources.proto
+++ b/src/devtools/mobileharness/fe/v6/service/proto/host/host_resources.proto
@@ -152,10 +152,17 @@ message ReleaseDetails {
   repeated CommandRecord async_commands = 4;
 }
 
+enum VersionStatus {
+  VERSION_STATUS_UNSPECIFIED = 0;
+  LATEST = 1;
+  CURRENT = 2;
+  LATEST_AND_CURRENT = 3;
+}
+
 message DeployableVersion {
-  string name = 1;        // Release name
-  string version = 2;     // Version string (e.g. "v4.358.0")
-  string status = 3;      // "Latest", "Current", or empty
+  string name = 1;     // Release name
+  string version = 2;  // Version string (e.g. "v4.358.0")
+  VersionStatus status = 3;
   string build_time = 4;  // Build timestamp
   repeated ReleasePort ports = 5;
   ReleaseDetails release_details = 6;
diff --git a/src/devtools/mobileharness/fe/v6/service/proto/host/host_service.proto b/src/devtools/mobileharness/fe/v6/service/proto/host/host_service.proto
index 1f52f94039..2c8b2ea07a 100644
--- a/src/devtools/mobileharness/fe/v6/service/proto/host/host_service.proto
+++ b/src/devtools/mobileharness/fe/v6/service/proto/host/host_service.proto
@@ -227,7 +227,24 @@ message UpdatePassThroughFlagsRequest {
 }
 
 // Response message for UpdatePassThroughFlags.
-message UpdatePassThroughFlagsResponse {}
+message UpdatePassThroughFlagsResponse {
+  bool success = 1;
+  Error error = 2;
+
+  message Error {
+    Code code = 1;
+    string message = 2;
+
+    enum Code {
+      CODE_UNSPECIFIED = 0;
+      PERMISSION_DENIED = 1;
+      INVALID_FLAGS = 2;
+      HOST_NOT_FOUND = 3;
+      WARPGATE_ERROR = 4;
+      UNKNOWN = 5;
+    }
+  }
+}
 
 // Request message for PreflightLabServerRelease.
 message PreflightLabServerReleaseRequest {
diff --git a/src/java/com/google/devtools/mobileharness/fe/v6/service/host/HostServiceGrpcImpl.java b/src/java/com/google/devtools/mobileharness/fe/v6/service/host/HostServiceGrpcImpl.java
index 6d522e726f..9081f3a6df 100644
--- a/src/java/com/google/devtools/mobileharness/fe/v6/service/host/HostServiceGrpcImpl.java
+++ b/src/java/com/google/devtools/mobileharness/fe/v6/service/host/HostServiceGrpcImpl.java
@@ -133,7 +133,7 @@ public void updatePassThroughFlags(
     GrpcServiceUtil.invokeAsync(
         request,
         responseObserver,
-        logic::updatePassThroughFlags,
+        req -> logic.updatePassThroughFlags(req, Optional.empty()),
         executor,
         HostServiceGrpc.getServiceDescriptor(),
         HostServiceGrpc.getUpdatePassThroughFlagsMethod());
@@ -146,7 +146,7 @@ public void preflightLabServerRelease(
     GrpcServiceUtil.invokeAsync(
         request,
         responseObserver,
-        logic::preflightLabServerRelease,
+        req -> logic.preflightLabServerRelease(req, Optional.empty()),
         executor,
         HostServiceGrpc.getServiceDescriptor(),
         HostServiceGrpc.getPreflightLabServerReleaseMethod());
diff --git a/src/java/com/google/devtools/mobileharness/fe/v6/service/host/HostServiceLogic.java b/src/java/com/google/devtools/mobileharness/fe/v6/service/host/HostServiceLogic.java
index 5bc1450dcd..cdf8bca41d 100644
--- a/src/java/com/google/devtools/mobileharness/fe/v6/service/host/HostServiceLogic.java
+++ b/src/java/com/google/devtools/mobileharness/fe/v6/service/host/HostServiceLogic.java
@@ -63,10 +63,10 @@ ListenableFuture<GetHostDeviceSummariesResponse> getHostDeviceSummaries(
   ListenableFuture<GetPopularFlagsResponse> getPopularFlags(GetPopularFlagsRequest request);
 
   ListenableFuture<UpdatePassThroughFlagsResponse> updatePassThroughFlags(
-      UpdatePassThroughFlagsRequest request);
+      UpdatePassThroughFlagsRequest request, Optional<String> username);
 
   ListenableFuture<PreflightLabServerReleaseResponse> preflightLabServerRelease(
-      PreflightLabServerReleaseRequest request);
+      PreflightLabServerReleaseRequest request, Optional<String> username);
 
   ListenableFuture<DecommissionMissingDevicesResponse> decommissionMissingDevices(
       DecommissionMissingDevicesRequest request);
diff --git a/src/java/com/google/devtools/mobileharness/fe/v6/service/host/HostServiceLogicImpl.java b/src/java/com/google/devtools/mobileharness/fe/v6/service/host/HostServiceLogicImpl.java
index fde3539e5c..06c30dd855 100644
--- a/src/java/com/google/devtools/mobileharness/fe/v6/service/host/HostServiceLogicImpl.java
+++ b/src/java/com/google/devtools/mobileharness/fe/v6/service/host/HostServiceLogicImpl.java
@@ -25,7 +25,9 @@
 import com.google.devtools.mobileharness.fe.v6.service.host.handlers.GetHostDeviceSummariesHandler;
 import com.google.devtools.mobileharness.fe.v6.service.host.handlers.GetHostHeaderInfoHandler;
 import com.google.devtools.mobileharness.fe.v6.service.host.handlers.GetHostOverviewHandler;
+import com.google.devtools.mobileharness.fe.v6.service.host.handlers.PreflightLabServerReleaseHandler;
 import com.google.devtools.mobileharness.fe.v6.service.host.handlers.RemoteControlDevicesHandler;
+import com.google.devtools.mobileharness.fe.v6.service.host.handlers.UpdatePassThroughFlagsHandler;
 import com.google.devtools.mobileharness.fe.v6.service.proto.host.CheckRemoteControlEligibilityRequest;
 import com.google.devtools.mobileharness.fe.v6.service.proto.host.CheckRemoteControlEligibilityResponse;
 import com.google.devtools.mobileharness.fe.v6.service.proto.host.DecommissionHostRequest;
@@ -72,6 +74,8 @@ public final class HostServiceLogicImpl implements HostServiceLogic {
   private final RemoteControlDevicesHandler remoteControlDevicesHandler;
   private final GetHostHeaderInfoHandler getHostHeaderInfoHandler;
   private final DecommissionMissingDevicesHandler decommissionMissingDevicesHandler;
+  private final PreflightLabServerReleaseHandler preflightLabServerReleaseHandler;
+  private final UpdatePassThroughFlagsHandler updatePassThroughFlagsHandler;
   private final UniverseFactory universeFactory;
 
   @Inject
@@ -82,6 +86,8 @@ public final class HostServiceLogicImpl implements HostServiceLogic {
       RemoteControlDevicesHandler remoteControlDevicesHandler,
       GetHostHeaderInfoHandler getHostHeaderInfoHandler,
       DecommissionMissingDevicesHandler decommissionMissingDevicesHandler,
+      PreflightLabServerReleaseHandler preflightLabServerReleaseHandler,
+      UpdatePassThroughFlagsHandler updatePassThroughFlagsHandler,
       UniverseFactory universeFactory) {
     this.getHostOverviewHandler = getHostOverviewHandler;
     this.getHostDeviceSummariesHandler = getHostDeviceSummariesHandler;
@@ -89,6 +95,8 @@ public final class HostServiceLogicImpl implements HostServiceLogic {
     this.remoteControlDevicesHandler = remoteControlDevicesHandler;
     this.getHostHeaderInfoHandler = getHostHeaderInfoHandler;
     this.decommissionMissingDevicesHandler = decommissionMissingDevicesHandler;
+    this.preflightLabServerReleaseHandler = preflightLabServerReleaseHandler;
+    this.updatePassThroughFlagsHandler = updatePassThroughFlagsHandler;
     this.universeFactory = universeFactory;
   }
 
@@ -147,22 +155,26 @@ public ListenableFuture<GetPopularFlagsResponse> getPopularFlags(GetPopularFlags
 
   @Override
   public ListenableFuture<UpdatePassThroughFlagsResponse> updatePassThroughFlags(
-      UpdatePassThroughFlagsRequest request) {
-    // TODO: Use the universe parameter.
-    @SuppressWarnings("unused")
-    String universe = request.getUniverse();
-    // TODO: Implement this method.
-    return immediateFuture(UpdatePassThroughFlagsResponse.getDefaultInstance());
+      UpdatePassThroughFlagsRequest request, Optional<String> username) {
+    UniverseScope universe;
+    try {
+      universe = universeFactory.create(request.getUniverse());
+    } catch (IllegalArgumentException e) {
+      return immediateFailedFuture(e);
+    }
+    return updatePassThroughFlagsHandler.updatePassThroughFlags(request, username, universe);
   }
 
   @Override
   public ListenableFuture<PreflightLabServerReleaseResponse> preflightLabServerRelease(
-      PreflightLabServerReleaseRequest request) {
-    // TODO: Use the universe parameter.
-    @SuppressWarnings("unused")
-    String universe = request.getUniverse();
-    // TODO: Implement this method.
-    return immediateFuture(PreflightLabServerReleaseResponse.getDefaultInstance());
+      PreflightLabServerReleaseRequest request, Optional<String> username) {
+    UniverseScope universe;
+    try {
+      universe = universeFactory.create(request.getUniverse());
+    } catch (IllegalArgumentException e) {
+      return immediateFailedFuture(e);
+    }
+    return preflightLabServerReleaseHandler.preflightLabServerRelease(request, universe, username);
   }
 
   @Override
diff --git a/src/java/com/google/devtools/mobileharness/fe/v6/service/host/handlers/NoOpPreflightLabServerReleaseActionHelper.java b/src/java/com/google/devtools/mobileharness/fe/v6/service/host/handlers/NoOpPreflightLabServerReleaseActionHelper.java
new file mode 100644
index 0000000000..6672a17ee2
--- /dev/null
+++ b/src/java/com/google/devtools/mobileharness/fe/v6/service/host/handlers/NoOpPreflightLabServerReleaseActionHelper.java
@@ -0,0 +1,44 @@
+/*
+ * Copyright 2022 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.devtools.mobileharness.fe.v6.service.host.handlers;
+
+import static com.google.common.util.concurrent.Futures.immediateFailedFuture;
+
+import com.google.common.util.concurrent.ListenableFuture;
+import com.google.devtools.mobileharness.fe.v6.service.proto.host.PreflightLabServerReleaseRequest;
+import com.google.devtools.mobileharness.fe.v6.service.proto.host.PreflightLabServerReleaseResponse;
+import com.google.devtools.mobileharness.fe.v6.service.util.UniverseScope;
+import java.util.Optional;
+import javax.inject.Inject;
+import javax.inject.Singleton;
+
+/** No-op implementation of {@link PreflightLabServerReleaseActionHelper}. */
+@Singleton
+public final class NoOpPreflightLabServerReleaseActionHelper
+    implements PreflightLabServerReleaseActionHelper {
+
+  @Inject
+  NoOpPreflightLabServerReleaseActionHelper() {}
+
+  @Override
+  public ListenableFuture<PreflightLabServerReleaseResponse> preflightLabServerRelease(
+      PreflightLabServerReleaseRequest request, UniverseScope universe, Optional<String> username) {
+    return immediateFailedFuture(
+        new UnsupportedOperationException(
+            "Preflight lab server release is not supported in the current environment."));
+  }
+}
diff --git a/src/java/com/google/devtools/mobileharness/fe/v6/service/host/handlers/NoOpUpdatePassThroughFlagsActionHelper.java b/src/java/com/google/devtools/mobileharness/fe/v6/service/host/handlers/NoOpUpdatePassThroughFlagsActionHelper.java
new file mode 100644
index 0000000000..4ef46817b0
--- /dev/null
+++ b/src/java/com/google/devtools/mobileharness/fe/v6/service/host/handlers/NoOpUpdatePassThroughFlagsActionHelper.java
@@ -0,0 +1,48 @@
+/*
+ * Copyright 2022 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.devtools.mobileharness.fe.v6.service.host.handlers;
+
+import static com.google.common.util.concurrent.Futures.immediateFuture;
+
+import com.google.common.util.concurrent.ListenableFuture;
+import com.google.devtools.mobileharness.fe.v6.service.proto.host.UpdatePassThroughFlagsRequest;
+import com.google.devtools.mobileharness.fe.v6.service.proto.host.UpdatePassThroughFlagsResponse;
+import com.google.devtools.mobileharness.fe.v6.service.proto.host.UpdatePassThroughFlagsResponse.Error;
+import com.google.devtools.mobileharness.fe.v6.service.proto.host.UpdatePassThroughFlagsResponse.Error.Code;
+import com.google.devtools.mobileharness.fe.v6.service.util.UniverseScope;
+import java.util.Optional;
+
+/** No-op implementation of {@link UpdatePassThroughFlagsActionHelper}. */
+public final class NoOpUpdatePassThroughFlagsActionHelper
+    implements UpdatePassThroughFlagsActionHelper {
+
+  NoOpUpdatePassThroughFlagsActionHelper() {}
+
+  @Override
+  public ListenableFuture<UpdatePassThroughFlagsResponse> updatePassThroughFlags(
+      UpdatePassThroughFlagsRequest request, Optional<String> username, UniverseScope universe) {
+    return immediateFuture(
+        UpdatePassThroughFlagsResponse.newBuilder()
+            .setSuccess(false)
+            .setError(
+                Error.newBuilder()
+                    .setCode(Code.PERMISSION_DENIED)
+                    .setMessage("Only supported internally")
+                    .build())
+            .build());
+  }
+}
diff --git a/src/java/com/google/devtools/mobileharness/fe/v6/service/host/handlers/PreflightLabServerReleaseActionHelper.java b/src/java/com/google/devtools/mobileharness/fe/v6/service/host/handlers/PreflightLabServerReleaseActionHelper.java
new file mode 100644
index 0000000000..7c70fa1fe4
--- /dev/null
+++ b/src/java/com/google/devtools/mobileharness/fe/v6/service/host/handlers/PreflightLabServerReleaseActionHelper.java
@@ -0,0 +1,30 @@
+/*
+ * Copyright 2022 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.devtools.mobileharness.fe.v6.service.host.handlers;
+
+import com.google.common.util.concurrent.ListenableFuture;
+import com.google.devtools.mobileharness.fe.v6.service.proto.host.PreflightLabServerReleaseRequest;
+import com.google.devtools.mobileharness.fe.v6.service.proto.host.PreflightLabServerReleaseResponse;
+import com.google.devtools.mobileharness.fe.v6.service.util.UniverseScope;
+import java.util.Optional;
+
+/** Helper for {@link PreflightLabServerReleaseHandler}. */
+public interface PreflightLabServerReleaseActionHelper {
+
+  ListenableFuture<PreflightLabServerReleaseResponse> preflightLabServerRelease(
+      PreflightLabServerReleaseRequest request, UniverseScope universe, Optional<String> username);
+}
diff --git a/src/java/com/google/devtools/mobileharness/fe/v6/service/host/handlers/PreflightLabServerReleaseHandler.java b/src/java/com/google/devtools/mobileharness/fe/v6/service/host/handlers/PreflightLabServerReleaseHandler.java
new file mode 100644
index 0000000000..e1445c2d47
--- /dev/null
+++ b/src/java/com/google/devtools/mobileharness/fe/v6/service/host/handlers/PreflightLabServerReleaseHandler.java
@@ -0,0 +1,44 @@
+/*
+ * Copyright 2022 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.devtools.mobileharness.fe.v6.service.host.handlers;
+
+import com.google.common.util.concurrent.ListenableFuture;
+import com.google.devtools.mobileharness.fe.v6.service.proto.host.PreflightLabServerReleaseRequest;
+import com.google.devtools.mobileharness.fe.v6.service.proto.host.PreflightLabServerReleaseResponse;
+import com.google.devtools.mobileharness.fe.v6.service.util.UniverseScope;
+import java.util.Optional;
+import javax.inject.Inject;
+import javax.inject.Singleton;
+
+/** Handler for the PreflightLabServerRelease RPC. */
+@Singleton
+public final class PreflightLabServerReleaseHandler {
+
+  private final PreflightLabServerReleaseActionHelper preflightLabServerReleaseActionHelper;
+
+  @Inject
+  PreflightLabServerReleaseHandler(
+      PreflightLabServerReleaseActionHelper preflightLabServerReleaseActionHelper) {
+    this.preflightLabServerReleaseActionHelper = preflightLabServerReleaseActionHelper;
+  }
+
+  public ListenableFuture<PreflightLabServerReleaseResponse> preflightLabServerRelease(
+      PreflightLabServerReleaseRequest request, UniverseScope universe, Optional<String> username) {
+    return preflightLabServerReleaseActionHelper.preflightLabServerRelease(
+        request, universe, username);
+  }
+}
diff --git a/src/java/com/google/devtools/mobileharness/fe/v6/service/host/handlers/UpdatePassThroughFlagsActionHelper.java b/src/java/com/google/devtools/mobileharness/fe/v6/service/host/handlers/UpdatePassThroughFlagsActionHelper.java
new file mode 100644
index 0000000000..9c33185429
--- /dev/null
+++ b/src/java/com/google/devtools/mobileharness/fe/v6/service/host/handlers/UpdatePassThroughFlagsActionHelper.java
@@ -0,0 +1,30 @@
+/*
+ * Copyright 2022 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.devtools.mobileharness.fe.v6.service.host.handlers;
+
+import com.google.common.util.concurrent.ListenableFuture;
+import com.google.devtools.mobileharness.fe.v6.service.proto.host.UpdatePassThroughFlagsRequest;
+import com.google.devtools.mobileharness.fe.v6.service.proto.host.UpdatePassThroughFlagsResponse;
+import com.google.devtools.mobileharness.fe.v6.service.util.UniverseScope;
+import java.util.Optional;
+
+/** Helper for {@link UpdatePassThroughFlagsHandler}. */
+public interface UpdatePassThroughFlagsActionHelper {
+
+  ListenableFuture<UpdatePassThroughFlagsResponse> updatePassThroughFlags(
+      UpdatePassThroughFlagsRequest request, Optional<String> username, UniverseScope universe);
+}
diff --git a/src/java/com/google/devtools/mobileharness/fe/v6/service/host/handlers/UpdatePassThroughFlagsHandler.java b/src/java/com/google/devtools/mobileharness/fe/v6/service/host/handlers/UpdatePassThroughFlagsHandler.java
new file mode 100644
index 0000000000..6c8d1c9f4d
--- /dev/null
+++ b/src/java/com/google/devtools/mobileharness/fe/v6/service/host/handlers/UpdatePassThroughFlagsHandler.java
@@ -0,0 +1,40 @@
+/*
+ * Copyright 2022 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.devtools.mobileharness.fe.v6.service.host.handlers;
+
+import com.google.common.util.concurrent.ListenableFuture;
+import com.google.devtools.mobileharness.fe.v6.service.proto.host.UpdatePassThroughFlagsRequest;
+import com.google.devtools.mobileharness.fe.v6.service.proto.host.UpdatePassThroughFlagsResponse;
+import com.google.devtools.mobileharness.fe.v6.service.util.UniverseScope;
+import java.util.Optional;
+import javax.inject.Inject;
+
+/** Handler for updating pass through flags. */
+public final class UpdatePassThroughFlagsHandler {
+
+  private final UpdatePassThroughFlagsActionHelper actionHelper;
+
+  @Inject
+  UpdatePassThroughFlagsHandler(UpdatePassThroughFlagsActionHelper actionHelper) {
+    this.actionHelper = actionHelper;
+  }
+
+  public ListenableFuture<UpdatePassThroughFlagsResponse> updatePassThroughFlags(
+      UpdatePassThroughFlagsRequest request, Optional<String> username, UniverseScope universe) {
+    return actionHelper.updatePassThroughFlags(request, username, universe);
+  }
+}
diff --git a/src/java/com/google/devtools/mobileharness/fe/v6/service/shared/BUILD b/src/java/com/google/devtools/mobileharness/fe/v6/service/shared/BUILD
index 9b7f3f4321..45b8847eca 100644
--- a/src/java/com/google/devtools/mobileharness/fe/v6/service/shared/BUILD
+++ b/src/java/com/google/devtools/mobileharness/fe/v6/service/shared/BUILD
@@ -60,6 +60,7 @@ java_library(
         "//src/java/com/google/devtools/mobileharness/fe/v6/service/device/handlers:logcat_action_helper",
         "//src/java/com/google/devtools/mobileharness/fe/v6/service/device/handlers:screenshot_action_helper",
         "//src/java/com/google/devtools/mobileharness/fe/v6/service/host/builder",
+        "//src/java/com/google/devtools/mobileharness/fe/v6/service/host/handlers",
         "//src/java/com/google/devtools/mobileharness/fe/v6/service/host/provider",
         "//src/java/com/google/devtools/mobileharness/fe/v6/service/shared/auth",
         "//src/java/com/google/devtools/mobileharness/fe/v6/service/shared/providers:configuration_provider",
diff --git a/src/java/com/google/devtools/mobileharness/fe/v6/service/shared/OssStubsModule.java b/src/java/com/google/devtools/mobileharness/fe/v6/service/shared/OssStubsModule.java
index 8d03f07e04..b0d00206ff 100644
--- a/src/java/com/google/devtools/mobileharness/fe/v6/service/shared/OssStubsModule.java
+++ b/src/java/com/google/devtools/mobileharness/fe/v6/service/shared/OssStubsModule.java
@@ -29,6 +29,10 @@
 import com.google.devtools.mobileharness.fe.v6.service.device.handlers.TestbedConfigBuilder;
 import com.google.devtools.mobileharness.fe.v6.service.host.builder.NoOpRemoteControlUrlBuilder;
 import com.google.devtools.mobileharness.fe.v6.service.host.builder.RemoteControlUrlBuilder;
+import com.google.devtools.mobileharness.fe.v6.service.host.handlers.NoOpPreflightLabServerReleaseActionHelper;
+import com.google.devtools.mobileharness.fe.v6.service.host.handlers.NoOpUpdatePassThroughFlagsActionHelper;
+import com.google.devtools.mobileharness.fe.v6.service.host.handlers.PreflightLabServerReleaseActionHelper;
+import com.google.devtools.mobileharness.fe.v6.service.host.handlers.UpdatePassThroughFlagsActionHelper;
 import com.google.devtools.mobileharness.fe.v6.service.host.provider.HostAuxiliaryInfoProvider;
 import com.google.devtools.mobileharness.fe.v6.service.host.provider.OssHostAuxiliaryInfoProviderImpl;
 import com.google.devtools.mobileharness.fe.v6.service.shared.auth.GroupMembershipProvider;
@@ -91,6 +95,12 @@ protected void configure() {
         .in(Singleton.class);
 
     bind(HostAuxiliaryInfoProvider.class).to(OssHostAuxiliaryInfoProviderImpl.class);
+    bind(PreflightLabServerReleaseActionHelper.class)
+        .to(NoOpPreflightLabServerReleaseActionHelper.class)
+        .in(Singleton.class);
+    bind(UpdatePassThroughFlagsActionHelper.class)
+        .to(NoOpUpdatePassThroughFlagsActionHelper.class)
+        .in(Singleton.class);
     bind(LogcatActionHelper.class).to(NoOpLogcatActionHelper.class).in(Singleton.class);
     bind(RemoteControlUrlBuilder.class).to(NoOpRemoteControlUrlBuilder.class);
     bind(ScreenshotActionHelper.class).to(NoOpScreenshotActionHelper.class).in(Singleton.class);
diff --git a/src/java/com/google/devtools/mobileharness/fe/v6/service/util/FeatureReadiness.java b/src/java/com/google/devtools/mobileharness/fe/v6/service/util/FeatureReadiness.java
index ffaa76b310..ea7e69f72d 100644
--- a/src/java/com/google/devtools/mobileharness/fe/v6/service/util/FeatureReadiness.java
+++ b/src/java/com/google/devtools/mobileharness/fe/v6/service/util/FeatureReadiness.java
@@ -63,7 +63,7 @@ public boolean isLabServerStopReady() {
   }
 
   public boolean isLabServerReleaseReady() {
-    return false;
+    return true;
   }
 
   public boolean isLabServerDeployReady() {
diff --git a/src/javatests/com/google/devtools/mobileharness/fe/v6/service/host/BUILD b/src/javatests/com/google/devtools/mobileharness/fe/v6/service/host/BUILD
index e9e7949cba..b2c0e61027 100644
--- a/src/javatests/com/google/devtools/mobileharness/fe/v6/service/host/BUILD
+++ b/src/javatests/com/google/devtools/mobileharness/fe/v6/service/host/BUILD
@@ -30,6 +30,7 @@ java_library(
         "//src/devtools/mobileharness/shared/labinfo/proto:lab_info_service_java_proto",
         "//src/java/com/google/devtools/mobileharness/fe/v6/service/host:host_service_logic_impl",
         "//src/java/com/google/devtools/mobileharness/fe/v6/service/host/builder",
+        "//src/java/com/google/devtools/mobileharness/fe/v6/service/host/handlers",
         "//src/java/com/google/devtools/mobileharness/fe/v6/service/host/provider",
         "//src/java/com/google/devtools/mobileharness/fe/v6/service/shared",
         "//src/java/com/google/devtools/mobileharness/fe/v6/service/shared/providers:lab_info_provider",
diff --git a/src/javatests/com/google/devtools/mobileharness/fe/v6/service/host/HostServiceLogicImplTest.java b/src/javatests/com/google/devtools/mobileharness/fe/v6/service/host/HostServiceLogicImplTest.java
index 912e7d20d1..36c519166c 100644
--- a/src/javatests/com/google/devtools/mobileharness/fe/v6/service/host/HostServiceLogicImplTest.java
+++ b/src/javatests/com/google/devtools/mobileharness/fe/v6/service/host/HostServiceLogicImplTest.java
@@ -26,9 +26,13 @@
 
 import com.google.common.util.concurrent.ListeningExecutorService;
 import com.google.devtools.mobileharness.fe.v6.service.host.builder.RemoteControlUrlBuilder;
+import com.google.devtools.mobileharness.fe.v6.service.host.handlers.PreflightLabServerReleaseActionHelper;
+import com.google.devtools.mobileharness.fe.v6.service.host.handlers.UpdatePassThroughFlagsActionHelper;
 import com.google.devtools.mobileharness.fe.v6.service.host.provider.HostAuxiliaryInfoProvider;
 import com.google.devtools.mobileharness.fe.v6.service.proto.host.GetHostHeaderInfoRequest;
 import com.google.devtools.mobileharness.fe.v6.service.proto.host.HostHeaderInfo;
+import com.google.devtools.mobileharness.fe.v6.service.proto.host.PreflightLabServerReleaseRequest;
+import com.google.devtools.mobileharness.fe.v6.service.proto.host.PreflightLabServerReleaseResponse;
 import com.google.devtools.mobileharness.fe.v6.service.shared.SubDeviceInfoListFactory;
 import com.google.devtools.mobileharness.fe.v6.service.shared.providers.LabInfoProvider;
 import com.google.devtools.mobileharness.fe.v6.service.shared.remotecontrol.RemoteControlEligibilityChecker;
@@ -68,6 +72,8 @@ public final class HostServiceLogicImplTest {
   @Bind @Mock private InstantSource instantSource;
   @Bind @Mock private FeatureManagerFactory featureManagerFactory;
   @Bind @Mock private LabSyncStub labSyncStub;
+  @Bind @Mock private PreflightLabServerReleaseActionHelper preflightLabServerReleaseActionHelper;
+  @Bind @Mock private UpdatePassThroughFlagsActionHelper updatePassThroughFlagsActionHelper;
   @Mock private FeatureManager featureManager;
 
   private HostServiceLogicImpl hostServiceLogicImpl;
@@ -109,4 +115,35 @@ public void getHostHeaderInfo_invalidUniverse_fails() throws Exception {
             ExecutionException.class, () -> hostServiceLogicImpl.getHostHeaderInfo(request).get());
     assertThat(e).hasCauseThat().isInstanceOf(IllegalArgumentException.class);
   }
+
+  @Test
+  public void preflightLabServerRelease_success() throws Exception {
+    PreflightLabServerReleaseRequest request =
+        PreflightLabServerReleaseRequest.newBuilder().setUniverse("universe").build();
+    PreflightLabServerReleaseResponse response =
+        PreflightLabServerReleaseResponse.getDefaultInstance();
+
+    when(preflightLabServerReleaseActionHelper.preflightLabServerRelease(any(), any(), any()))
+        .thenReturn(immediateFuture(response));
+
+    PreflightLabServerReleaseResponse actualResponse =
+        hostServiceLogicImpl.preflightLabServerRelease(request, Optional.of("user")).get();
+
+    assertThat(actualResponse).isEqualTo(response);
+  }
+
+  @Test
+  public void preflightLabServerRelease_invalidUniverse_fails() throws Exception {
+    PreflightLabServerReleaseRequest request =
+        PreflightLabServerReleaseRequest.newBuilder().setUniverse("invalid").build();
+
+    when(universeFactory.create("invalid")).thenThrow(new IllegalArgumentException("invalid"));
+
+    ExecutionException e =
+        assertThrows(
+            ExecutionException.class,
+            () ->
+                hostServiceLogicImpl.preflightLabServerRelease(request, Optional.of("user")).get());
+    assertThat(e).hasCauseThat().isInstanceOf(IllegalArgumentException.class);
+  }
 }
diff --git a/src/javatests/com/google/devtools/mobileharness/fe/v6/service/host/handlers/PreflightLabServerReleaseHandlerTest.java b/src/javatests/com/google/devtools/mobileharness/fe/v6/service/host/handlers/PreflightLabServerReleaseHandlerTest.java
new file mode 100644
index 0000000000..f609189cd8
--- /dev/null
+++ b/src/javatests/com/google/devtools/mobileharness/fe/v6/service/host/handlers/PreflightLabServerReleaseHandlerTest.java
@@ -0,0 +1,80 @@
+/*
+ * Copyright 2022 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.devtools.mobileharness.fe.v6.service.host.handlers;
+
+import static com.google.common.truth.Truth.assertThat;
+import static com.google.common.util.concurrent.Futures.immediateFuture;
+import static org.mockito.ArgumentMatchers.eq;
+import static org.mockito.Mockito.when;
+
+import com.google.common.util.concurrent.Futures;
+import com.google.common.util.concurrent.ListenableFuture;
+import com.google.devtools.mobileharness.fe.v6.service.proto.host.PreflightLabServerReleaseRequest;
+import com.google.devtools.mobileharness.fe.v6.service.proto.host.PreflightLabServerReleaseResponse;
+import com.google.devtools.mobileharness.fe.v6.service.util.UniverseScope;
+import com.google.inject.Guice;
+import com.google.inject.testing.fieldbinder.Bind;
+import com.google.inject.testing.fieldbinder.BoundFieldModule;
+import java.util.Optional;
+import javax.inject.Inject;
+import org.junit.Before;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+import org.mockito.Mock;
+import org.mockito.junit.MockitoJUnit;
+import org.mockito.junit.MockitoRule;
+
+@RunWith(JUnit4.class)
+public final class PreflightLabServerReleaseHandlerTest {
+
+  private static final String USERNAME = "test-user";
+  private static final String HOST_NAME = "test-host";
+  private static final PreflightLabServerReleaseRequest REQUEST =
+      PreflightLabServerReleaseRequest.newBuilder().setHostName(HOST_NAME).build();
+  private static final UniverseScope UNIVERSE = new UniverseScope.SelfUniverse();
+
+  @Rule public final MockitoRule mocks = MockitoJUnit.rule();
+
+  @Bind @Mock private PreflightLabServerReleaseActionHelper actionHelper;
+
+  @Inject private PreflightLabServerReleaseHandler handler;
+
+  @Before
+  public void setUp() {
+    Guice.createInjector(BoundFieldModule.of(this)).injectMembers(this);
+  }
+
+  @Test
+  public void preflight_delegatesToActionHelper() throws Exception {
+    PreflightLabServerReleaseResponse expectedResponse =
+        PreflightLabServerReleaseResponse.newBuilder()
+            .setReady(PreflightLabServerReleaseResponse.ReleaseReady.getDefaultInstance())
+            .build();
+
+    when(actionHelper.preflightLabServerRelease(
+            eq(REQUEST), eq(UNIVERSE), eq(Optional.of(USERNAME))))
+        .thenReturn(immediateFuture(expectedResponse));
+
+    ListenableFuture<PreflightLabServerReleaseResponse> resultFuture =
+        handler.preflightLabServerRelease(REQUEST, UNIVERSE, Optional.of(USERNAME));
+
+    PreflightLabServerReleaseResponse response = Futures.getDone(resultFuture);
+    assertThat(response).isEqualTo(expectedResponse);
+  }
+}
diff --git a/src/javatests/com/google/devtools/mobileharness/fe/v6/service/util/FeatureReadinessTest.java b/src/javatests/com/google/devtools/mobileharness/fe/v6/service/util/FeatureReadinessTest.java
index f0e86f19c0..965c71250a 100644
--- a/src/javatests/com/google/devtools/mobileharness/fe/v6/service/util/FeatureReadinessTest.java
+++ b/src/javatests/com/google/devtools/mobileharness/fe/v6/service/util/FeatureReadinessTest.java
@@ -72,4 +72,9 @@ public void isHostDecommissionReady_returnsFalse() {
   public void isLabServerStartReady_returnsTrue() {
     assertThat(featureReadiness.isLabServerStartReady()).isTrue();
   }
+
+  @Test
+  public void isLabServerReleaseReady_returnsTrue() {
+    assertThat(featureReadiness.isLabServerReleaseReady()).isTrue();
+  }
 }