diff --git a/open-sse/mcp-server/server.ts b/open-sse/mcp-server/server.ts
index c584b7a75d..9f8a536744 100644
--- a/open-sse/mcp-server/server.ts
+++ b/open-sse/mcp-server/server.ts
@@ -46,6 +46,7 @@ import {
   type McpToolExtraLike,
 } from "./scopeEnforcement.ts";
 import { getMcpHttpAuthHeadersForInternalFetch } from "./httpAuthContext.ts";
+import { getInternalServiceAuthHeaders } from "../../src/lib/api/internalServiceAuth.ts";
 import {
   handleSimulateRoute,
   handleSetBudgetGuard,
@@ -203,6 +204,9 @@ export async function omniRouteFetch(path: string, options: RequestInit = {}): P
     ...(apiKey ? { Authorization: `Bearer ${apiKey}` } : {}),
     ...getMcpHttpAuthHeadersForInternalFetch(),
     ...((options.headers as Record<string, string>) || {}),
+    // Authenticate only the server-to-server hop. This does not replace or
+    // weaken the caller identity forwarded above.
+    ...getInternalServiceAuthHeaders(),
   };
 
   const signal = options.signal || AbortSignal.timeout(10000);
diff --git a/src/lib/api/internalServiceAuth.ts b/src/lib/api/internalServiceAuth.ts
new file mode 100644
index 0000000000..f09cff90f6
--- /dev/null
+++ b/src/lib/api/internalServiceAuth.ts
@@ -0,0 +1,39 @@
+import { readFileSync } from "node:fs";
+import { timingSafeEqual } from "node:crypto";
+import { AUTHZ_HEADER_PEER_LOCALITY } from "@/server/authz/headers";
+
+export const INTERNAL_SERVICE_AUTH_HEADER = "x-omniroute-internal-service-token";
+
+function configuredToken(): string {
+  const inlineToken = process.env.OMNIROUTE_INTERNAL_SERVICE_TOKEN?.trim();
+  if (inlineToken) return inlineToken;
+
+  const tokenFile = process.env.OMNIROUTE_INTERNAL_SERVICE_TOKEN_FILE?.trim();
+  if (!tokenFile) return "";
+
+  try {
+    return readFileSync(tokenFile, "utf8").trim();
+  } catch {
+    return "";
+  }
+}
+
+export function getInternalServiceAuthHeaders(): Record<string, string> {
+  const token = configuredToken();
+  return token ? { [INTERNAL_SERVICE_AUTH_HEADER]: token } : {};
+}
+
+export function isInternalServiceRequest(request: Request): boolean {
+  const expected = configuredToken();
+  const provided = request.headers.get(INTERNAL_SERVICE_AUTH_HEADER)?.trim() || "";
+  if (!expected || !provided || expected.length !== provided.length) return false;
+
+  return timingSafeEqual(Buffer.from(provided, "utf8"), Buffer.from(expected, "utf8"));
+}
+
+export function isTrustedLoopbackInternalServiceRequest(request: Request): boolean {
+  return (
+    request.headers.get(AUTHZ_HEADER_PEER_LOCALITY) === "loopback" &&
+    isInternalServiceRequest(request)
+  );
+}
diff --git a/src/lib/api/requireManagementAuth.ts b/src/lib/api/requireManagementAuth.ts
index 8540d17c20..eb0dc99239 100644
--- a/src/lib/api/requireManagementAuth.ts
+++ b/src/lib/api/requireManagementAuth.ts
@@ -4,6 +4,7 @@ import { extractApiKey, isValidApiKey } from "@/sse/services/auth";
 import { getApiKeyMetadata } from "@/lib/db/apiKeys";
 import { isCliTokenAuthValid } from "@/lib/middleware/cliTokenAuth";
 import { evaluateAccessTokenAuth } from "@/server/authz/accessTokenAuth";
+import { isTrustedLoopbackInternalServiceRequest } from "@/lib/api/internalServiceAuth";
 import {
   MANAGE_SCOPE,
   hasManageScope as hasManageScopeShared,
@@ -47,6 +48,10 @@ export async function requireManagementAuth(
     return null;
   }
 
+  if (isTrustedLoopbackInternalServiceRequest(request)) {
+    return null;
+  }
+
   // CLI machine-id token allows localhost CLI access without an explicit API key.
   if (await isCliTokenAuthValid(request)) {
     return null;
diff --git a/src/server/authz/policies/management.ts b/src/server/authz/policies/management.ts
index ee67cbfca2..a2949f3aa4 100644
--- a/src/server/authz/policies/management.ts
+++ b/src/server/authz/policies/management.ts
@@ -9,6 +9,7 @@ import { getApiKeyMetadata } from "../../../lib/db/apiKeys";
 import { hasManageScope } from "../../../lib/api/requireManagementAuth";
 import { hasMcpConnectOrManageScope, MCP_CONNECT_SCOPE } from "../../../shared/constants/managementScopes";
 import { evaluateAccessTokenAuth } from "../accessTokenAuth";
+import { isInternalServiceRequest } from "../../../lib/api/internalServiceAuth";
 import { CLI_TOKEN_HEADER, PEER_IP_HEADER, VIA_PROXY_HEADER } from "../headers";
 import { resolveStampedPeer, resolveStampedViaProxy } from "../peerStamp";
 import {
@@ -233,6 +234,14 @@ export const managementPolicy: RoutePolicy = {
       return allow({ kind: "management_key", id: "model-sync", label: "internal-model-sync" });
     }
 
+    if (isLoopbackRequest(ctx) && isInternalServiceRequest(ctx.request as unknown as Request)) {
+      return allow({
+        kind: "management_key",
+        id: "internal-service",
+        label: "internal-service-token",
+      });
+    }
+
     if (hasValidCliToken(ctx)) {
       return allow({ kind: "management_key", id: "cli", label: "local-cli-token" });
     }
diff --git a/tests/unit/authz/management-policy.test.ts b/tests/unit/authz/management-policy.test.ts
index 3f6e05a6b3..2e0e69a558 100644
--- a/tests/unit/authz/management-policy.test.ts
+++ b/tests/unit/authz/management-policy.test.ts
@@ -16,6 +16,7 @@ const core = await import("../../../src/lib/db/core.ts");
 const apiKeysDb = await import("../../../src/lib/db/apiKeys.ts");
 const settingsDb = await import("../../../src/lib/db/settings.ts");
 const modelSync = await import("../../../src/shared/services/modelSyncScheduler.ts");
+const internalServiceAuth = await import("../../../src/lib/api/internalServiceAuth.ts");
 
 const ORIGINAL_JWT = process.env.JWT_SECRET;
 const ORIGINAL_INITIAL = process.env.INITIAL_PASSWORD;
@@ -146,6 +147,26 @@ test("managementPolicy: rejects 401 when auth required and no credentials", asyn
   }
 });
 
+test("managementPolicy: allows a valid internal service token only from loopback", async () => {
+  process.env.JWT_SECRET = "test-jwt-secret-for-mgmt-policy";
+  process.env.INITIAL_PASSWORD = "initial-pass";
+  process.env.OMNIROUTE_INTERNAL_SERVICE_TOKEN = "internal-service-token-0123456789";
+  await settingsDb.updateSettings({ requireLogin: true });
+  const policy = await loadPolicy();
+  const headers = new Headers({
+    [internalServiceAuth.INTERNAL_SERVICE_AUTH_HEADER]: "internal-service-token-0123456789",
+  });
+
+  const loopback = await policy.evaluate(
+    ctx(headers, "GET", "/api/combos", { socket: { remoteAddress: "127.0.0.1" } })
+  );
+  assert.equal(loopback.allow, true);
+
+  const remote = await policy.evaluate(remoteCtx(headers, "GET", "/api/combos"));
+  assert.equal(remote.allow, false);
+  delete process.env.OMNIROUTE_INTERNAL_SERVICE_TOKEN;
+});
+
 test("managementPolicy: rejects client API keys for dashboard access", async () => {
   process.env.JWT_SECRET = "test-jwt-secret-for-mgmt-policy";
   process.env.INITIAL_PASSWORD = "initial-pass";
diff --git a/tests/unit/internal-service-auth.test.ts b/tests/unit/internal-service-auth.test.ts
new file mode 100644
index 0000000000..3ff053ab01
--- /dev/null
+++ b/tests/unit/internal-service-auth.test.ts
@@ -0,0 +1,66 @@
+import test from "node:test";
+import assert from "node:assert/strict";
+import fs from "node:fs";
+import os from "node:os";
+import path from "node:path";
+
+import {
+  getInternalServiceAuthHeaders,
+  INTERNAL_SERVICE_AUTH_HEADER,
+  isInternalServiceRequest,
+  isTrustedLoopbackInternalServiceRequest,
+} from "../../src/lib/api/internalServiceAuth.ts";
+import { AUTHZ_HEADER_PEER_LOCALITY } from "../../src/server/authz/headers.ts";
+
+const originalInline = process.env.OMNIROUTE_INTERNAL_SERVICE_TOKEN;
+const originalFile = process.env.OMNIROUTE_INTERNAL_SERVICE_TOKEN_FILE;
+
+test.afterEach(() => {
+  if (originalInline === undefined) delete process.env.OMNIROUTE_INTERNAL_SERVICE_TOKEN;
+  else process.env.OMNIROUTE_INTERNAL_SERVICE_TOKEN = originalInline;
+  if (originalFile === undefined) delete process.env.OMNIROUTE_INTERNAL_SERVICE_TOKEN_FILE;
+  else process.env.OMNIROUTE_INTERNAL_SERVICE_TOKEN_FILE = originalFile;
+});
+
+test("internal service auth is disabled when no token is configured", () => {
+  delete process.env.OMNIROUTE_INTERNAL_SERVICE_TOKEN;
+  delete process.env.OMNIROUTE_INTERNAL_SERVICE_TOKEN_FILE;
+  assert.deepEqual(getInternalServiceAuthHeaders(), {});
+  assert.equal(isInternalServiceRequest(new Request("http://localhost")), false);
+});
+
+test("internal service auth preserves a separate constant-time token channel", () => {
+  process.env.OMNIROUTE_INTERNAL_SERVICE_TOKEN = "test-internal-token-0123456789";
+  delete process.env.OMNIROUTE_INTERNAL_SERVICE_TOKEN_FILE;
+  const headers = new Headers({
+    ...getInternalServiceAuthHeaders(),
+    [AUTHZ_HEADER_PEER_LOCALITY]: "loopback",
+  });
+  const request = new Request("http://localhost", { headers });
+  assert.equal(headers.get(INTERNAL_SERVICE_AUTH_HEADER), "test-internal-token-0123456789");
+  assert.equal(isInternalServiceRequest(request), true);
+  assert.equal(isTrustedLoopbackInternalServiceRequest(request), true);
+
+  const remote = new Request("https://example.test", {
+    headers: {
+      [INTERNAL_SERVICE_AUTH_HEADER]: "test-internal-token-0123456789",
+      [AUTHZ_HEADER_PEER_LOCALITY]: "remote",
+    },
+  });
+  assert.equal(isTrustedLoopbackInternalServiceRequest(remote), false);
+});
+
+test("internal service token file is read without exposing it to process env", () => {
+  const directory = fs.mkdtempSync(path.join(os.tmpdir(), "omr-internal-auth-"));
+  const tokenFile = path.join(directory, "token");
+  try {
+    fs.writeFileSync(tokenFile, "file-backed-token-0123456789\n", { mode: 0o600 });
+    delete process.env.OMNIROUTE_INTERNAL_SERVICE_TOKEN;
+    process.env.OMNIROUTE_INTERNAL_SERVICE_TOKEN_FILE = tokenFile;
+    assert.deepEqual(getInternalServiceAuthHeaders(), {
+      [INTERNAL_SERVICE_AUTH_HEADER]: "file-backed-token-0123456789",
+    });
+  } finally {
+    fs.rmSync(directory, { recursive: true, force: true });
+  }
+});
diff --git a/tests/unit/require-management-auth-access-token.test.ts b/tests/unit/require-management-auth-access-token.test.ts
index 985e0d39c1..d99674df78 100644
--- a/tests/unit/require-management-auth-access-token.test.ts
+++ b/tests/unit/require-management-auth-access-token.test.ts
@@ -34,6 +34,27 @@ test.after(() => {
     fs.rmSync(TEST_DATA_DIR, { recursive: true, force: true });
   } catch {}
   delete process.env.INITIAL_PASSWORD;
+  delete process.env.OMNIROUTE_INTERNAL_SERVICE_TOKEN;
+});
+
+test("internal service token requires the trusted loopback locality marker", async () => {
+  process.env.OMNIROUTE_INTERNAL_SERVICE_TOKEN = "internal-service-token-0123456789";
+  const tokenHeader = "x-omniroute-internal-service-token";
+  const local = new Request(`${BASE}/api/combos`, {
+    headers: {
+      [tokenHeader]: "internal-service-token-0123456789",
+      "x-omniroute-peer-locality": "loopback",
+    },
+  });
+  assert.equal(await requireManagementAuth(local), null);
+
+  const remote = new Request(`${BASE}/api/combos`, {
+    headers: {
+      [tokenHeader]: "internal-service-token-0123456789",
+      "x-omniroute-peer-locality": "remote",
+    },
+  });
+  assert.equal((await requireManagementAuth(remote))?.status, 401);
 });
 
 test("read token: allowed on GET, rejected (403) on a write route", async () => {