diff --git a/packages/api/src/endpoints/custom/initialize.ts b/packages/api/src/endpoints/custom/initialize.ts
index e25b5e1d34..0d334878ec 100644
--- a/packages/api/src/endpoints/custom/initialize.ts
+++ b/packages/api/src/endpoints/custom/initialize.ts
@@ -115,7 +115,7 @@ function buildCustomOptions(
   }
 
   const allConfig = appConfig?.endpoints?.all;
-  if (allConfig) {
+  if (allConfig?.streamRate != null) {
     customOptions.streamRate = allConfig.streamRate;
   }
 
@@ -345,7 +345,7 @@ export async function initializeCustom({
   }
 
   const streamRate = clientOptions.streamRate as number | undefined;
-  if (streamRate) {
+  if (streamRate != null) {
     (options.llmConfig as Record<string, unknown>)._lc_stream_delay = streamRate;
   }
 
diff --git a/packages/api/src/endpoints/custom/streamrate.spec.ts b/packages/api/src/endpoints/custom/streamrate.spec.ts
new file mode 100644
index 0000000000..fa6aae9244
--- /dev/null
+++ b/packages/api/src/endpoints/custom/streamrate.spec.ts
@@ -0,0 +1,104 @@
+import type { BaseInitializeParams } from '~/types';
+
+jest.mock('~/auth', () => ({
+  validateEndpointURL: jest.fn(),
+  createSSRFSafeUndiciConnect: jest.fn(() => ({ lookup: jest.fn() })),
+}));
+
+const mockGetOpenAIConfig = jest.fn((..._args: unknown[]) => ({
+  llmConfig: { model: 'claude-haiku-4-5' } as Record<string, unknown>,
+  configOptions: {},
+}));
+jest.mock('~/endpoints/openai/config', () => ({
+  getOpenAIConfig: (...args: unknown[]) => mockGetOpenAIConfig(...args),
+}));
+
+jest.mock('~/endpoints/models', () => ({ fetchModels: jest.fn() }));
+jest.mock('~/cache', () => ({
+  standardCache: jest.fn(() => ({ get: jest.fn().mockResolvedValue(null) })),
+  tokenConfigCache: jest.fn(() => ({ get: jest.fn().mockResolvedValue(null) })),
+}));
+jest.mock('~/utils', () => ({
+  isUserProvided: (val: string) => val === 'user_provided',
+  checkUserKeyExpiry: jest.fn(),
+}));
+
+const mockGetCustomEndpointConfig = jest.fn();
+jest.mock('~/app/config', () => ({
+  getCustomEndpointConfig: (...args: unknown[]) => mockGetCustomEndpointConfig(...args),
+}));
+
+import { initializeCustom } from './initialize';
+
+function makeParams({
+  allBlock,
+  endpointStreamRate,
+}: {
+  allBlock?: Record<string, unknown>;
+  endpointStreamRate?: number;
+} = {}): BaseInitializeParams {
+  mockGetCustomEndpointConfig.mockReturnValue({
+    apiKey: 'test-key',
+    baseURL: 'https://gateway.example.com/v1',
+    models: { default: ['claude-haiku-4-5'], fetch: false },
+    streamRate: endpointStreamRate,
+  });
+
+  return {
+    req: {
+      user: { id: 'user-1' },
+      body: {},
+      config: allBlock ? { endpoints: { all: allBlock } } : {},
+    } as unknown as BaseInitializeParams['req'],
+    endpoint: 'ClickHouse',
+    model_parameters: { model: 'claude-haiku-4-5' },
+    db: { getUserKeyValues: jest.fn() } as unknown as BaseInitializeParams['db'],
+  };
+}
+
+function streamDelayOf(options: { llmConfig: unknown }): unknown {
+  return (options.llmConfig as Record<string, unknown>)._lc_stream_delay;
+}
+
+describe('custom endpoint streamRate resolution', () => {
+  beforeEach(() => jest.clearAllMocks());
+
+  it('applies the endpoint streamRate when no `endpoints.all` block is present', async () => {
+    const options = await initializeCustom(makeParams({ endpointStreamRate: 25 }));
+    expect(streamDelayOf(options)).toBe(25);
+  });
+
+  it('preserves the endpoint streamRate when `endpoints.all` exists without its own streamRate', async () => {
+    const options = await initializeCustom(
+      makeParams({
+        endpointStreamRate: 25,
+        allBlock: { activityLabel: true, activityModel: 'gpt-5.6-luna' },
+      }),
+    );
+    expect(streamDelayOf(options)).toBe(25);
+  });
+
+  it('lets `endpoints.all.streamRate` override the endpoint streamRate', async () => {
+    const options = await initializeCustom(
+      makeParams({ endpointStreamRate: 25, allBlock: { streamRate: 10 } }),
+    );
+    expect(streamDelayOf(options)).toBe(10);
+  });
+
+  it('leaves the stream delay unset when neither level configures a streamRate', async () => {
+    const options = await initializeCustom(makeParams({ allBlock: { activityLabel: true } }));
+    expect(streamDelayOf(options)).toBeUndefined();
+  });
+
+  it('lets `endpoints.all.streamRate: 0` override an endpoint streamRate (explicit disable)', async () => {
+    const options = await initializeCustom(
+      makeParams({ endpointStreamRate: 25, allBlock: { streamRate: 0 } }),
+    );
+    expect(streamDelayOf(options)).toBe(0);
+  });
+
+  it('passes an explicit endpoint `streamRate: 0` through to the llmConfig', async () => {
+    const options = await initializeCustom(makeParams({ endpointStreamRate: 0 }));
+    expect(streamDelayOf(options)).toBe(0);
+  });
+});