diff --git a/apps/admin/.env.example b/apps/admin/.env.example
index b676155a4..bd8647fa7 100644
--- a/apps/admin/.env.example
+++ b/apps/admin/.env.example
@@ -1,6 +1,7 @@
-# API 서버 URL (필수)
-# 빌드/프리뷰 시 이 값이 없으면 API 호출은 실패하지만 SSR shell은 500 없이 응답해야 합니다.
-VITE_API_SERVER_URL=https://api.example.com
+# API 서버 URL (로컬 개발 전용 override, 선택)
+# 설정 시 로그인 계정의 이메일 패턴과 무관하게 이 값이 항상 사용됩니다.
+# 비워두면 로그인한 계정의 이메일 도메인에 따라 dev/prod API가 런타임에 자동 선택됩니다.
+# VITE_API_SERVER_URL=http://localhost:8080
 
 # 업로드 CDN URL (선택)
 VITE_UPLOADED_IMAGE_URL=https://cdn.upload.solid-connection.com
diff --git a/apps/admin/src/components/features/bruno/BrunoApiPageContent.tsx b/apps/admin/src/components/features/bruno/BrunoApiPageContent.tsx
index 77c1b54e7..32b239497 100644
--- a/apps/admin/src/components/features/bruno/BrunoApiPageContent.tsx
+++ b/apps/admin/src/components/features/bruno/BrunoApiPageContent.tsx
@@ -15,6 +15,7 @@ import { Table, TableBody, TableCell, TableHead, TableHeader, TableRow } from "@
 import { Tabs, TabsContent, TabsList, TabsTrigger } from "@/components/ui/tabs";
 import { Textarea } from "@/components/ui/textarea";
 import { axiosInstance } from "@/lib/api/client";
+import { resolveActiveApiBaseUrl } from "@/lib/env";
 import { cn } from "@/lib/utils";
 
 type EndpointItem = BrunoApiDefinitionRegistryItem;
@@ -46,7 +47,6 @@ const ALL_ENDPOINTS: EndpointItem[] = [...brunoApiDefinitionRegistry].sort((a, b
 const METHOD_FILTERS: MethodFilter[] = ["ALL", "GET", "POST", "PUT", "PATCH", "DELETE", "HEAD", "OPTIONS"];
 const MUTATING_METHODS = new Set<DefinitionMethod>(["POST", "PUT", "PATCH", "DELETE"]);
 const METHODS_WITHOUT_BODY = new Set<string>(["GET", "HEAD"]);
-const apiServerUrl = import.meta.env.VITE_API_SERVER_URL?.trim() ?? "";
 
 const toPrettyJson = (value: unknown): string => {
 	if (value === undefined) {
@@ -199,7 +199,7 @@ export function BrunoApiPageContent() {
 	const remoteWarningUrl =
 		selectedEndpoint && isAbsoluteUrl(selectedEndpoint.definition.path)
 			? selectedEndpoint.definition.path
-			: apiServerUrl;
+			: resolveActiveApiBaseUrl();
 	const showRemoteWarning = isRemoteApiServer(remoteWarningUrl);
 
 	useEffect(() => {
diff --git a/apps/admin/src/components/features/chat-socket/ChatSocketPageContent.tsx b/apps/admin/src/components/features/chat-socket/ChatSocketPageContent.tsx
index 17dad5190..eceba4a2c 100644
--- a/apps/admin/src/components/features/chat-socket/ChatSocketPageContent.tsx
+++ b/apps/admin/src/components/features/chat-socket/ChatSocketPageContent.tsx
@@ -10,6 +10,7 @@ import { Button } from "@/components/ui/button";
 import { Card, CardContent, CardHeader, CardTitle } from "@/components/ui/card";
 import { Input } from "@/components/ui/input";
 import { Textarea } from "@/components/ui/textarea";
+import { resolveActiveApiBaseUrl } from "@/lib/env";
 import { loadAccessToken } from "@/lib/utils/localStorage";
 
 type ConnectionState = "DISCONNECTED" | "CONNECTING" | "CONNECTED" | "ERROR";
@@ -92,7 +93,7 @@ export function ChatSocketPageContent() {
 	const subscriptionRef = useRef<StompSubscription | null>(null);
 
 	const [connectionState, setConnectionState] = useState<ConnectionState>("DISCONNECTED");
-	const [serverUrl, setServerUrl] = useState(import.meta.env.VITE_API_SERVER_URL?.trim() ?? "");
+	const [serverUrl, setServerUrl] = useState(resolveActiveApiBaseUrl());
 	const [token, setToken] = useState("");
 	const [roomId, setRoomId] = useState("");
 	const [topicTemplate, setTopicTemplate] = useState(defaultTopicTemplate);
diff --git a/apps/admin/src/components/layout/AdminLayout.tsx b/apps/admin/src/components/layout/AdminLayout.tsx
index edea0cfc6..785409f91 100644
--- a/apps/admin/src/components/layout/AdminLayout.tsx
+++ b/apps/admin/src/components/layout/AdminLayout.tsx
@@ -6,6 +6,7 @@ import { toast } from "sonner";
 import { adminSignOutApi } from "@/lib/api/auth";
 import { clearSession } from "@/lib/auth/session";
 import { type ActiveAdminMenu, AdminSidebar } from "./AdminSidebar";
+import { EnvironmentBanner } from "./EnvironmentBanner";
 
 interface AdminLayoutProps {
 	children: React.ReactNode;
@@ -51,6 +52,7 @@ export function AdminLayout({ children, activeMenu, title, description }: AdminL
 						</div>
 					</div>
 					<div className="flex items-center gap-2">
+						<EnvironmentBanner />
 						<p className="hidden rounded-full bg-bg-50 px-3 py-1 typo-medium-4 text-k-600 sm:block">운영 콘솔</p>
 						<button
 							type="button"
diff --git a/apps/admin/src/components/layout/EnvironmentBanner.tsx b/apps/admin/src/components/layout/EnvironmentBanner.tsx
new file mode 100644
index 000000000..b4af87353
--- /dev/null
+++ b/apps/admin/src/components/layout/EnvironmentBanner.tsx
@@ -0,0 +1,50 @@
+"use client";
+
+import { useEffect, useState } from "react";
+import { getAdminApiServerUrl } from "@/lib/env";
+import { loadAdminApiEnvironment } from "@/lib/utils/localStorage";
+
+type DisplayedEnvironment = "dev" | "prod" | "local";
+
+const environmentStyles: Record<DisplayedEnvironment, string> = {
+	dev: "bg-magic-success-surface text-magic-success",
+	prod: "bg-magic-danger-surface text-magic-danger",
+	local: "bg-bg-50 text-k-600",
+};
+
+const environmentLabels: Record<DisplayedEnvironment, string> = {
+	dev: "DEV",
+	prod: "PROD",
+	local: "LOCAL",
+};
+
+const resolveDisplayedEnvironment = (): DisplayedEnvironment => {
+	if (import.meta.env.DEV && getAdminApiServerUrl()) {
+		return "local";
+	}
+	return loadAdminApiEnvironment() ?? "prod";
+};
+
+export function EnvironmentBanner() {
+	const [environment, setEnvironment] = useState<DisplayedEnvironment | null>(null);
+
+	useEffect(() => {
+		setEnvironment(resolveDisplayedEnvironment());
+
+		const handleStorageChange = () => setEnvironment(resolveDisplayedEnvironment());
+		window.addEventListener("storage", handleStorageChange);
+		return () => window.removeEventListener("storage", handleStorageChange);
+	}, []);
+
+	if (!environment) {
+		return null;
+	}
+
+	return (
+		<span
+			className={`inline-flex items-center rounded-full px-2.5 py-0.5 typo-medium-4 ${environmentStyles[environment]}`}
+		>
+			{environmentLabels[environment]}
+		</span>
+	);
+}
diff --git a/apps/admin/src/lib/api/auth.test.ts b/apps/admin/src/lib/api/auth.test.ts
new file mode 100644
index 000000000..966a4d2e3
--- /dev/null
+++ b/apps/admin/src/lib/api/auth.test.ts
@@ -0,0 +1,60 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+
+const { post, requestInterceptors } = vi.hoisted(() => ({
+	post: vi.fn().mockResolvedValue({ data: { accessToken: "token" } }),
+	requestInterceptors: [] as Array<(config: Record<string, unknown>) => Record<string, unknown>>,
+}));
+
+vi.mock("axios", () => ({
+	default: {
+		create: () => ({
+			post,
+			interceptors: {
+				request: {
+					use: (fn: (config: Record<string, unknown>) => Record<string, unknown>) => {
+						requestInterceptors.push(fn);
+					},
+				},
+			},
+		}),
+	},
+}));
+
+describe("adminSignInApi", () => {
+	beforeEach(() => {
+		post.mockClear();
+		localStorage.clear();
+	});
+
+	afterEach(() => {
+		vi.restoreAllMocks();
+	});
+
+	it("dev 이메일 로그인 요청은 localStorage 저장 성공 여부와 무관하게 stage baseURL로 전송된다", async () => {
+		const setItemSpy = vi.spyOn(Storage.prototype, "setItem").mockImplementation(() => {
+			throw new Error("storage unavailable");
+		});
+
+		const { adminSignInApi } = await import("./auth");
+		await adminSignInApi("admin@dev.solid-connection.com", "password");
+
+		expect(post).toHaveBeenCalledWith(
+			"/auth/email/sign-in",
+			{ email: "admin@dev.solid-connection.com", password: "password" },
+			{ baseURL: "https://api.stage.solid-connection.com" },
+		);
+
+		setItemSpy.mockRestore();
+	});
+
+	it("prod 이메일 로그인 요청은 prod baseURL로 전송된다", async () => {
+		const { adminSignInApi } = await import("./auth");
+		await adminSignInApi("admin@solid-connection.com", "password");
+
+		expect(post).toHaveBeenCalledWith(
+			"/auth/email/sign-in",
+			{ email: "admin@solid-connection.com", password: "password" },
+			{ baseURL: "https://api.solid-connection.com" },
+		);
+	});
+});
diff --git a/apps/admin/src/lib/api/auth.ts b/apps/admin/src/lib/api/auth.ts
index 49507fd0a..970f86670 100644
--- a/apps/admin/src/lib/api/auth.ts
+++ b/apps/admin/src/lib/api/auth.ts
@@ -1,34 +1,43 @@
 import axios, { type AxiosResponse } from "axios";
-import { createMissingAdminApiServerUrlError, getAdminApiServerUrl } from "@/lib/env";
-import { loadAccessToken } from "@/lib/utils/localStorage";
+import { getApiBaseUrlForEnvironment, resolveEnvironmentFromEmail } from "@/lib/auth/environment";
+import { resolveActiveApiBaseUrl } from "@/lib/env";
+import { loadAccessToken, removeAccessToken, saveAdminApiEnvironment } from "@/lib/utils/localStorage";
 import type { AdminSignInResponse, ReissueAccessTokenResponse } from "@/types/auth";
 
-const API_SERVER_URL = getAdminApiServerUrl();
-
 const authAxiosInstance = axios.create({
-	baseURL: API_SERVER_URL || undefined,
 	withCredentials: true,
 });
 
-const assertAdminApiServerUrl = () => {
-	if (!API_SERVER_URL) {
-		throw createMissingAdminApiServerUrlError();
-	}
-};
+authAxiosInstance.interceptors.request.use((config) => {
+	const newConfig = { ...config };
+	// Respect an explicitly-provided baseURL (e.g. adminSignInApi pinning the just-resolved
+	// environment) instead of always re-deriving it from potentially-unavailable storage.
+	newConfig.baseURL = config.baseURL ?? resolveActiveApiBaseUrl();
+	return newConfig;
+});
 
 export const adminSignInApi = (email: string, password: string): Promise<AxiosResponse<AdminSignInResponse>> => {
-	assertAdminApiServerUrl();
-	return authAxiosInstance.post("/auth/email/sign-in", { email, password });
+	const environment = resolveEnvironmentFromEmail(email);
+
+	// Clear any previous environment's token before switching, so a stale token can never
+	// ride along to the newly resolved environment's API (e.g. dev token leaking to prod).
+	removeAccessToken();
+	saveAdminApiEnvironment(environment);
+
+	// Pin this request's baseURL directly instead of relying on a localStorage round trip:
+	// if storage is unavailable, the request still goes to the correctly resolved environment.
+	return authAxiosInstance.post(
+		"/auth/email/sign-in",
+		{ email, password },
+		{ baseURL: getApiBaseUrlForEnvironment(environment) },
+	);
 };
 
 export const reissueAccessTokenApi = (): Promise<AxiosResponse<ReissueAccessTokenResponse>> => {
-	assertAdminApiServerUrl();
 	return authAxiosInstance.post("/auth/reissue");
 };
 
 export const adminSignOutApi = (): Promise<AxiosResponse<void>> => {
-	assertAdminApiServerUrl();
-
 	const accessToken = loadAccessToken();
 
 	return authAxiosInstance.post("/auth/sign-out", undefined, {
diff --git a/apps/admin/src/lib/api/client.ts b/apps/admin/src/lib/api/client.ts
index ecb4b70bd..3703a8a27 100644
--- a/apps/admin/src/lib/api/client.ts
+++ b/apps/admin/src/lib/api/client.ts
@@ -1,13 +1,10 @@
 import axios, { type AxiosInstance, type InternalAxiosRequestConfig } from "axios";
 import { clearSession, ensureSessionToken, reissueAccessTokenIfPossible } from "@/lib/auth/session";
-import { createMissingAdminApiServerUrlError, getAdminApiServerUrl } from "@/lib/env";
+import { resolveActiveApiBaseUrl } from "@/lib/env";
 
 const convertToBearer = (token: string) => `Bearer ${token}`;
 
-const API_SERVER_URL = getAdminApiServerUrl();
-
 export const axiosInstance: AxiosInstance = axios.create({
-	baseURL: API_SERVER_URL || undefined,
 	withCredentials: true,
 });
 
@@ -19,11 +16,8 @@ const redirectToLogin = () => {
 
 axiosInstance.interceptors.request.use(
 	async (config) => {
-		if (!API_SERVER_URL) {
-			return Promise.reject(createMissingAdminApiServerUrlError());
-		}
-
 		const newConfig = { ...config };
+		newConfig.baseURL = resolveActiveApiBaseUrl();
 		const accessToken = await ensureSessionToken();
 
 		if (!accessToken) {
diff --git a/apps/admin/src/lib/auth/environment.test.ts b/apps/admin/src/lib/auth/environment.test.ts
new file mode 100644
index 000000000..df95ee3bc
--- /dev/null
+++ b/apps/admin/src/lib/auth/environment.test.ts
@@ -0,0 +1,28 @@
+import { describe, expect, it } from "vitest";
+import { getApiBaseUrlForEnvironment, resolveEnvironmentFromEmail } from "./environment";
+
+describe("resolveEnvironmentFromEmail", () => {
+	it("dev 도메인 이메일은 dev 환경으로 판별한다", () => {
+		expect(resolveEnvironmentFromEmail("admin@dev.solid-connection.com")).toBe("dev");
+	});
+
+	it("대소문자와 앞뒤 공백을 무시하고 판별한다", () => {
+		expect(resolveEnvironmentFromEmail("  Admin@Dev.Solid-Connection.Com  ")).toBe("dev");
+	});
+
+	it("dev 도메인이 아닌 이메일은 prod 환경으로 판별한다", () => {
+		expect(resolveEnvironmentFromEmail("admin@solid-connection.com")).toBe("prod");
+	});
+
+	it("dev 도메인을 부분 문자열로만 포함하는 이메일은 prod로 판별한다", () => {
+		expect(resolveEnvironmentFromEmail("admin@notdev.solid-connection.com")).toBe("prod");
+		expect(resolveEnvironmentFromEmail("admin@dev.solid-connection.com.evil.com")).toBe("prod");
+	});
+});
+
+describe("getApiBaseUrlForEnvironment", () => {
+	it("환경에 맞는 API base URL을 반환한다", () => {
+		expect(getApiBaseUrlForEnvironment("dev")).toBe("https://api.stage.solid-connection.com");
+		expect(getApiBaseUrlForEnvironment("prod")).toBe("https://api.solid-connection.com");
+	});
+});
diff --git a/apps/admin/src/lib/auth/environment.ts b/apps/admin/src/lib/auth/environment.ts
new file mode 100644
index 000000000..6d5a4450c
--- /dev/null
+++ b/apps/admin/src/lib/auth/environment.ts
@@ -0,0 +1,15 @@
+export type AdminApiEnvironment = "dev" | "prod";
+
+const DEV_EMAIL_DOMAIN = "dev.solid-connection.com";
+
+const API_BASE_URLS: Record<AdminApiEnvironment, string> = {
+	dev: "https://api.stage.solid-connection.com",
+	prod: "https://api.solid-connection.com",
+};
+
+export const resolveEnvironmentFromEmail = (email: string): AdminApiEnvironment => {
+	const normalizedEmail = email.trim().toLowerCase();
+	return normalizedEmail.endsWith(`@${DEV_EMAIL_DOMAIN}`) ? "dev" : "prod";
+};
+
+export const getApiBaseUrlForEnvironment = (environment: AdminApiEnvironment): string => API_BASE_URLS[environment];
diff --git a/apps/admin/src/lib/auth/session.ts b/apps/admin/src/lib/auth/session.ts
index 336d226fb..93104ee88 100644
--- a/apps/admin/src/lib/auth/session.ts
+++ b/apps/admin/src/lib/auth/session.ts
@@ -1,6 +1,11 @@
 import { reissueAccessTokenApi } from "@/lib/api/auth";
 import { isTokenExpired } from "@/lib/utils/jwtUtils";
-import { loadAccessToken, removeAccessToken, saveAccessToken } from "@/lib/utils/localStorage";
+import {
+	loadAccessToken,
+	removeAccessToken,
+	removeAdminApiEnvironment,
+	saveAccessToken,
+} from "@/lib/utils/localStorage";
 
 let reissuePromise: Promise<string | null> | null = null;
 let sessionVersion = 0;
@@ -23,6 +28,7 @@ export const clearSession = () => {
 	sessionVersion += 1;
 	reissuePromise = null;
 	removeAccessToken();
+	removeAdminApiEnvironment();
 };
 
 export const reissueAccessTokenIfPossible = async (): Promise<string | null> => {
diff --git a/apps/admin/src/lib/env.ts b/apps/admin/src/lib/env.ts
index eae7cada0..fc83b62e5 100644
--- a/apps/admin/src/lib/env.ts
+++ b/apps/admin/src/lib/env.ts
@@ -1,6 +1,21 @@
+import { getApiBaseUrlForEnvironment } from "@/lib/auth/environment";
+import { loadAdminApiEnvironment } from "@/lib/utils/localStorage";
+
 const getTrimmedEnv = (key: string) => import.meta.env[key]?.trim() ?? "";
 
+// Local-dev-only override (e.g. http://localhost:8080). When unset, the API server
+// is resolved at runtime from the signed-in account's environment (see resolveActiveApiBaseUrl).
 export const getAdminApiServerUrl = () => getTrimmedEnv("VITE_API_SERVER_URL");
 
-export const createMissingAdminApiServerUrlError = () =>
-	new Error("[admin] VITE_API_SERVER_URL is required. Configure it in your environment.");
+export const resolveActiveApiBaseUrl = (): string => {
+	// The override only applies to `vinext dev` (import.meta.env.DEV). Deployed builds
+	// (Preview/Production) always resolve dev/prod from the signed-in account's email,
+	// regardless of whether VITE_API_SERVER_URL happens to still be set on Vercel.
+	const localOverride = import.meta.env.DEV ? getAdminApiServerUrl() : "";
+	if (localOverride) {
+		return localOverride;
+	}
+
+	const storedEnvironment = loadAdminApiEnvironment();
+	return getApiBaseUrlForEnvironment(storedEnvironment ?? "prod");
+};
diff --git a/apps/admin/src/lib/utils/localStorage.ts b/apps/admin/src/lib/utils/localStorage.ts
index d4d285da1..b1776bc74 100644
--- a/apps/admin/src/lib/utils/localStorage.ts
+++ b/apps/admin/src/lib/utils/localStorage.ts
@@ -1,3 +1,7 @@
+import type { AdminApiEnvironment } from "@/lib/auth/environment";
+
+const ADMIN_API_ENVIRONMENT_KEY = "adminApiEnvironment";
+
 export const loadAccessToken = () => {
 	try {
 		return localStorage.getItem("accessToken");
@@ -22,3 +26,33 @@ export const removeAccessToken = () => {
 		console.error("Could not remove access token", err);
 	}
 };
+
+export const loadAdminApiEnvironment = (): AdminApiEnvironment | null => {
+	if (typeof window === "undefined") {
+		return null;
+	}
+
+	try {
+		const value = localStorage.getItem(ADMIN_API_ENVIRONMENT_KEY);
+		return value === "dev" || value === "prod" ? value : null;
+	} catch (err) {
+		console.error("Could not load admin api environment", err);
+		return null;
+	}
+};
+
+export const saveAdminApiEnvironment = (environment: AdminApiEnvironment) => {
+	try {
+		localStorage.setItem(ADMIN_API_ENVIRONMENT_KEY, environment);
+	} catch (err) {
+		console.error("Could not save admin api environment", err);
+	}
+};
+
+export const removeAdminApiEnvironment = () => {
+	try {
+		localStorage.removeItem(ADMIN_API_ENVIRONMENT_KEY);
+	} catch (err) {
+		console.error("Could not remove admin api environment", err);
+	}
+};