From 5611ff40e7ace8157fbeee97d459178e988862f3 Mon Sep 17 00:00:00 2001
From: Adam Weidman <65992621+adamfweidman@users.noreply.github.com>
Date: Sun, 17 May 2026 13:38:34 -0400
Subject: [PATCH] feat(core): add adk.agentSessionSubagentEnabled flag (#26947)

---
 docs/reference/configuration.md                |  6 ++++++
 packages/cli/src/config/settingsSchema.test.ts | 12 ++++++++++++
 packages/cli/src/config/settingsSchema.ts      | 10 ++++++++++
 packages/core/src/config/config.ts             |  8 ++++++++
 schemas/settings.schema.json                   |  7 +++++++
 5 files changed, 43 insertions(+)

diff --git a/docs/reference/configuration.md b/docs/reference/configuration.md
index e2250a3dbb..37959b7f95 100644
--- a/docs/reference/configuration.md
+++ b/docs/reference/configuration.md
@@ -1854,6 +1854,12 @@ their corresponding top-level category object in your `settings.json` file.
   - **Default:** `false`
   - **Requires restart:** Yes
 
+- **`experimental.adk.agentSessionSubagentEnabled`** (boolean):
+  - **Description:** Route subagent invocations through the AgentSession
+    protocol instead of legacy executors.
+  - **Default:** `false`
+  - **Requires restart:** Yes
+
 - **`experimental.enableAgents`** (boolean):
   - **Description:** Enable local and remote subagents.
   - **Default:** `true`
diff --git a/packages/cli/src/config/settingsSchema.test.ts b/packages/cli/src/config/settingsSchema.test.ts
index 368302890d..914ef21a64 100644
--- a/packages/cli/src/config/settingsSchema.test.ts
+++ b/packages/cli/src/config/settingsSchema.test.ts
@@ -571,6 +571,18 @@ describe('SettingsSchema', () => {
       expect(agentSessionNoninteractiveEnabled.description).toBe(
         'Enable non-interactive agent sessions.',
       );
+
+      const agentSessionSubagentEnabled =
+        adk.properties.agentSessionSubagentEnabled;
+      expect(agentSessionSubagentEnabled).toBeDefined();
+      expect(agentSessionSubagentEnabled.type).toBe('boolean');
+      expect(agentSessionSubagentEnabled.category).toBe('Experimental');
+      expect(agentSessionSubagentEnabled.default).toBe(false);
+      expect(agentSessionSubagentEnabled.requiresRestart).toBe(true);
+      expect(agentSessionSubagentEnabled.showInDialog).toBe(false);
+      expect(agentSessionSubagentEnabled.description).toBe(
+        'Route subagent invocations through the AgentSession protocol instead of legacy executors.',
+      );
     });
   });
 
diff --git a/packages/cli/src/config/settingsSchema.ts b/packages/cli/src/config/settingsSchema.ts
index 610f2e2a61..e3d68415e9 100644
--- a/packages/cli/src/config/settingsSchema.ts
+++ b/packages/cli/src/config/settingsSchema.ts
@@ -2194,6 +2194,16 @@ const SETTINGS_SCHEMA = {
               'Enable the agent session implementation for the interactive CLI.',
             showInDialog: false,
           },
+          agentSessionSubagentEnabled: {
+            type: 'boolean',
+            label: 'Agent Session Subagent Enabled',
+            category: 'Experimental',
+            requiresRestart: true,
+            default: false,
+            description:
+              'Route subagent invocations through the AgentSession protocol instead of legacy executors.',
+            showInDialog: false,
+          },
         },
       },
       enableAgents: {
diff --git a/packages/core/src/config/config.ts b/packages/core/src/config/config.ts
index 1568207936..18ff941cfd 100644
--- a/packages/core/src/config/config.ts
+++ b/packages/core/src/config/config.ts
@@ -237,6 +237,7 @@ export interface GemmaModelRouterSettings {
 export interface ADKSettings {
   agentSessionNoninteractiveEnabled?: boolean;
   agentSessionInteractiveEnabled?: boolean;
+  agentSessionSubagentEnabled?: boolean;
 }
 
 export interface ExtensionSetting {
@@ -913,6 +914,7 @@ export class Config implements McpContext, AgentLoopContext {
   private readonly gemmaModelRouter: GemmaModelRouterSettings;
   private readonly agentSessionNoninteractiveEnabled: boolean;
   private readonly agentSessionInteractiveEnabled: boolean;
+  private readonly agentSessionSubagentEnabled: boolean;
 
   private readonly retryFetchErrors: boolean;
   private readonly maxAttempts: number;
@@ -1359,6 +1361,8 @@ export class Config implements McpContext, AgentLoopContext {
       params.adk?.agentSessionNoninteractiveEnabled ?? false;
     this.agentSessionInteractiveEnabled =
       params.adk?.agentSessionInteractiveEnabled ?? false;
+    this.agentSessionSubagentEnabled =
+      params.adk?.agentSessionSubagentEnabled ?? false;
     this.retryFetchErrors = params.retryFetchErrors ?? true;
     this.maxAttempts = Math.min(
       params.maxAttempts ?? DEFAULT_MAX_ATTEMPTS,
@@ -2573,6 +2577,10 @@ export class Config implements McpContext, AgentLoopContext {
     return this.contextManagement.enabled;
   }
 
+  isAgentSessionSubagentEnabled(): boolean {
+    return this.agentSessionSubagentEnabled;
+  }
+
   getMemoryBoundaryMarkers(): readonly string[] {
     return this.memoryBoundaryMarkers;
   }
diff --git a/schemas/settings.schema.json b/schemas/settings.schema.json
index 2bcde8bc6f..d9d2e82989 100644
--- a/schemas/settings.schema.json
+++ b/schemas/settings.schema.json
@@ -3223,6 +3223,13 @@
               "markdownDescription": "Enable the agent session implementation for the interactive CLI.\n\n- Category: `Experimental`\n- Requires restart: `yes`\n- Default: `false`",
               "default": false,
               "type": "boolean"
+            },
+            "agentSessionSubagentEnabled": {
+              "title": "Agent Session Subagent Enabled",
+              "description": "Route subagent invocations through the AgentSession protocol instead of legacy executors.",
+              "markdownDescription": "Route subagent invocations through the AgentSession protocol instead of legacy executors.\n\n- Category: `Experimental`\n- Requires restart: `yes`\n- Default: `false`",
+              "default": false,
+              "type": "boolean"
             }
           },
           "additionalProperties": false