diff --git a/tools/ui/src/lib/services/chat.service.ts b/tools/ui/src/lib/services/chat.service.ts
index 7e652f99c5..31cefe3c9a 100644
--- a/tools/ui/src/lib/services/chat.service.ts
+++ b/tools/ui/src/lib/services/chat.service.ts
@@ -43,7 +43,7 @@ import type {
 	ApiStreamSession
 } from '$lib/types/api';
 import { isAbortError } from '$lib/utils/abort';
-import { apiUrl } from '$lib/utils/api-base';
+import { apiChatUrl, apiUrl } from '$lib/utils/api-base';
 import { ApiError } from '$lib/utils/api-fetch';
 import { getAuthHeaders, getJsonHeaders } from '$lib/utils/api-headers';
 import { formatAttachmentText } from '$lib/utils/formatters';
@@ -874,7 +874,7 @@ export class ChatService {
 		}
 
 		try {
-			await fetch(apiUrl(API_CHAT.COMPLETIONS), {
+			await fetch(apiChatUrl(), {
 				body: JSON.stringify(requestBody),
 				headers: getJsonHeaders(),
 				method: 'POST',
@@ -1235,7 +1235,7 @@ export class ChatService {
 				ChatService.saveStreamState(conversationId, 0, options.model ?? null);
 			}
 
-			const response = await fetch(apiUrl(API_CHAT.COMPLETIONS), {
+			const response = await fetch(apiChatUrl(), {
 				body: JSON.stringify(requestBody),
 				headers,
 				method: 'POST',
diff --git a/tools/ui/src/lib/services/models.service.ts b/tools/ui/src/lib/services/models.service.ts
index 710f5b8966..70b3d23208 100644
--- a/tools/ui/src/lib/services/models.service.ts
+++ b/tools/ui/src/lib/services/models.service.ts
@@ -12,6 +12,7 @@ import type { ParsedModelId } from '$lib/types/models';
 import {
 	apiDelete,
 	apiFetch,
+	apiModelsUrl,
 	apiPost,
 	apiUrl,
 	extractSseDataPayload,
@@ -140,7 +141,7 @@ export class ModelsService {
 	 * @returns List of available models with basic metadata
 	 */
 	static async list(): Promise<ApiModelsListResponse> {
-		return apiFetch<ApiModelsListResponse>(API_MODELS.LIST);
+		return apiFetch<ApiModelsListResponse>(apiModelsUrl());
 	}
 
 	/**
diff --git a/tools/ui/src/lib/utils/api-base.ts b/tools/ui/src/lib/utils/api-base.ts
index 07e8517200..d88d536531 100644
--- a/tools/ui/src/lib/utils/api-base.ts
+++ b/tools/ui/src/lib/utils/api-base.ts
@@ -7,8 +7,9 @@
  * store, which keeps URL resolution free of store dependencies.
  */
 
+import { backendChatUrl, backendModelsUrl } from './backend';
 import { base } from '$app/paths';
-import { API_ABSOLUTE_URL_PROTOCOLS } from '$lib/constants';
+import { API_ABSOLUTE_URL_PROTOCOLS, API_CHAT, API_MODELS } from '$lib/constants';
 import type { Backend } from '$lib/types';
 
 /** Backend list and active selection as exposed to URL resolution. */
@@ -44,6 +45,36 @@ export function getBackendBaseUrl(backendId?: string): string {
 	return getBackend(backendId)?.baseUrl.trim() ?? '';
 }
 
+/**
+ * Request target for a backend's chat completions endpoint. Returns a relative
+ * path for the local backend and an absolute URL for external ones, so callers
+ * can pass the result straight to `fetch` (or `apiFetch`, which resolves
+ * relative paths against the base).
+ */
+export function apiChatUrl(backendId?: string): string {
+	const backend = getBackend(backendId);
+
+	if (backend?.baseUrl.trim()) {
+		return backendChatUrl(backend);
+	}
+
+	return apiUrl(API_CHAT.COMPLETIONS, backendId);
+}
+
+/**
+ * Request target for a backend's models listing. Returns a plain path for the
+ * local backend (so `apiFetch` applies the base) and an absolute URL otherwise.
+ */
+export function apiModelsUrl(backendId?: string): string {
+	const backend = getBackend(backendId);
+
+	if (backend?.baseUrl.trim()) {
+		return backendModelsUrl(backend);
+	}
+
+	return API_MODELS.LIST;
+}
+
 /**
  * Absolute URL for an API path on a backend.
  *
diff --git a/tools/ui/src/lib/utils/index.ts b/tools/ui/src/lib/utils/index.ts
index 2278531bb3..f40d882029 100644
--- a/tools/ui/src/lib/utils/index.ts
+++ b/tools/ui/src/lib/utils/index.ts
@@ -8,7 +8,14 @@
  */
 
 // API utilities
-export { apiUrl, getBackend, getBackendBaseUrl, type BackendsSnapshot } from './api-base';
+export {
+	apiChatUrl,
+	apiModelsUrl,
+	apiUrl,
+	getBackend,
+	getBackendBaseUrl,
+	type BackendsSnapshot
+} from './api-base';
 export {
 	getAuthHeaders,
 	getAuthHeadersForBackend,