diff --git a/apps/calendar/apps/web/src/lib/api/birthdays.ts b/apps/calendar/apps/web/src/lib/api/birthdays.ts
index 224712a90..d5e73627c 100644
--- a/apps/calendar/apps/web/src/lib/api/birthdays.ts
+++ b/apps/calendar/apps/web/src/lib/api/birthdays.ts
@@ -28,6 +28,7 @@ function getContactsClient() {
 			getAuthToken: () => authStore.getValidToken(),
 			timeout: 30000,
 			debug: import.meta.env.DEV,
+			useRuntimeUrl: false,
 		});
 	}
 	return _contactsClient;
diff --git a/apps/calendar/apps/web/src/lib/api/todos.ts b/apps/calendar/apps/web/src/lib/api/todos.ts
index 4dea3385b..ba7891683 100644
--- a/apps/calendar/apps/web/src/lib/api/todos.ts
+++ b/apps/calendar/apps/web/src/lib/api/todos.ts
@@ -28,6 +28,7 @@ function getTodoClient() {
 			getAuthToken: () => authStore.getValidToken(),
 			timeout: 30000,
 			debug: import.meta.env.DEV,
+			useRuntimeUrl: false,
 		});
 	}
 	return _todoClient;
diff --git a/packages/shared-api-client/src/client.ts b/packages/shared-api-client/src/client.ts
index 1dfe1b395..a0d5b7c23 100644
--- a/packages/shared-api-client/src/client.ts
+++ b/packages/shared-api-client/src/client.ts
@@ -61,7 +61,7 @@ export function createApiClient(config: ApiClientConfig): ApiClient {
 		options: RequestOptions = {},
 		attemptNum = 0
 	): Promise<ApiResult<T>> {
-		const baseUrl = getBaseUrl(config.baseUrl);
+		const baseUrl = config.useRuntimeUrl !== false ? getBaseUrl(config.baseUrl) : config.baseUrl;
 		const queryString = options.params ? buildQueryString(options.params) : '';
 		const url = baseUrl + apiPrefix + endpoint + queryString;
 		const requestTimeout = options.timeout ?? timeout;
diff --git a/packages/shared-api-client/src/types.ts b/packages/shared-api-client/src/types.ts
index 1d39edfa7..96ceb14eb 100644
--- a/packages/shared-api-client/src/types.ts
+++ b/packages/shared-api-client/src/types.ts
@@ -62,6 +62,10 @@ export interface ApiClientConfig {
 
 	/** Enable debug logging (default: false) */
 	debug?: boolean;
+
+	/** Use window.__PUBLIC_BACKEND_URL__ runtime override (default: true).
+	 * Set to false for cross-app clients that resolve their own base URL. */
+	useRuntimeUrl?: boolean;
 }
 
 /**