diff --git a/.changeset/v2-model-catalog-efforts.md b/.changeset/v2-model-catalog-efforts.md
new file mode 100644
index 0000000000..36a52fa378
--- /dev/null
+++ b/.changeset/v2-model-catalog-efforts.md
@@ -0,0 +1,5 @@
+---
+"@moonshot-ai/agent-core-v2": patch
+---
+
+Fix the v2 model catalog response omitting support_efforts and default_effort, restoring thinking-effort selection for clients connected to the v2 backend.
diff --git a/packages/agent-core-v2/src/app/modelCatalog/modelCatalog.ts b/packages/agent-core-v2/src/app/modelCatalog/modelCatalog.ts
index be358af25b..66fc872f46 100644
--- a/packages/agent-core-v2/src/app/modelCatalog/modelCatalog.ts
+++ b/packages/agent-core-v2/src/app/modelCatalog/modelCatalog.ts
@@ -21,6 +21,7 @@ import type {
 import { createDecorator, type ServiceIdentifier } from '#/_base/di/instantiation';
 
 import type { ModelAlias } from '#/app/model/model';
+import { effectiveModelConfig } from '#/app/model/modelAuth';
 import type { ProviderConfig } from '#/app/provider/provider';
 
 export type RefreshProviderModelsScope = 'all' | 'oauth';
@@ -51,12 +52,15 @@ export interface ProviderCredentialState {
 }
 
 export function toProtocolModel(modelId: string, alias: ModelAlias): ModelCatalogItem {
+  const effective = effectiveModelConfig(alias);
   return {
-    provider: alias.provider ?? '',
+    provider: effective.provider ?? '',
     model: modelId,
-    display_name: alias.displayName ?? alias.model ?? modelId,
-    max_context_size: alias.maxContextSize ?? 0,
-    capabilities: alias.capabilities,
+    display_name: effective.displayName ?? effective.model ?? modelId,
+    max_context_size: effective.maxContextSize ?? 0,
+    capabilities: effective.capabilities,
+    support_efforts: effective.supportEfforts,
+    default_effort: effective.defaultEffort,
   };
 }
 
diff --git a/packages/agent-core-v2/test/app/modelCatalog/modelCatalog.test.ts b/packages/agent-core-v2/test/app/modelCatalog/modelCatalog.test.ts
index 5ac93de22e..a5ecc2e4de 100644
--- a/packages/agent-core-v2/test/app/modelCatalog/modelCatalog.test.ts
+++ b/packages/agent-core-v2/test/app/modelCatalog/modelCatalog.test.ts
@@ -159,6 +159,34 @@ describe('ModelCatalogService', () => {
     ]);
   });
 
+  it('projects support_efforts and default_effort from the model config', async () => {
+    backing.models['k2'] = {
+      ...backing.models['k2'],
+      supportEfforts: ['low', 'high', 'max'],
+      defaultEffort: 'max',
+    };
+    const [k2] = await catalog().listModels();
+    expect(k2).toMatchObject({
+      model: 'k2',
+      support_efforts: ['low', 'high', 'max'],
+      default_effort: 'max',
+    });
+  });
+
+  it('projects effort fields from overrides when present', async () => {
+    backing.models['k2'] = {
+      ...backing.models['k2'],
+      supportEfforts: ['low', 'high'],
+      defaultEffort: 'high',
+      overrides: { supportEfforts: ['low', 'high', 'max'], defaultEffort: 'max' },
+    };
+    const [k2] = await catalog().listModels();
+    expect(k2).toMatchObject({
+      support_efforts: ['low', 'high', 'max'],
+      default_effort: 'max',
+    });
+  });
+
   it('lists providers with per-provider models, default model, and credential state', async () => {
     await expect(catalog().listProviders()).resolves.toEqual([
       {