diff --git a/src/anthropic-proxy.ts b/src/anthropic-proxy.ts
index 147e7b0..932cf27 100644
--- a/src/anthropic-proxy.ts
+++ b/src/anthropic-proxy.ts
@@ -15,18 +15,35 @@ import { providerizeSchema } from "./json-schema";
 export type CreateAnthropicProxyOptions = {
   providers: Record<string, ProviderV2>;
   port?: number;
+  host?: string; // default: 127.0.0.1
+  authToken?: string; // if set, require matching custom header
+  authHeaderName?: string; // if authToken is set, required header name (default: X-AnyClaude-Token)
 };
 
 // createAnthropicProxy creates a proxy server that accepts
 // Anthropic Message API requests and proxies them through
 // the appropriate provider - converting the results back
 // to the Anthropic Message API format.
-export const createAnthropicProxy = ({
+export const createAnthropicProxy = async ({
   port,
+  host = "127.0.0.1",
   providers,
-}: CreateAnthropicProxyOptions): string => {
-  const proxy = http
-    .createServer((req, res) => {
+  authToken,
+  authHeaderName = "X-AnyClaude-Token",
+}: CreateAnthropicProxyOptions): Promise<string> => {
+  const proxy = http.createServer((req, res) => {
+      // Basic auth gate: require matching token via a custom header
+      if (authToken) {
+        const key = authHeaderName.toLowerCase();
+        const headerVal = req.headers[key];
+        const provided = Array.isArray(headerVal) ? headerVal[0] : headerVal;
+        if (!provided || provided !== authToken) {
+          res.writeHead(401, { "Content-Type": "application/json" });
+          res.end(JSON.stringify({ error: "Unauthorized" }));
+          return;
+        }
+      }
+
       if (!req.url) {
         res.writeHead(400, {
           "Content-Type": "application/json",
@@ -221,8 +238,18 @@ export const createAnthropicProxy = ({
           })
         );
       });
-    })
-    .listen(port ?? 0);
+  });
+
+  // Start listening using a random ephemeral port by default (0) and only
+  // resolve once the server has successfully bound, avoiding address() races.
+  const listenPort = typeof port === "number" ? port : 0;
+  await new Promise<void>((resolve, reject) => {
+    proxy.once("error", reject);
+    proxy.listen(listenPort, host, () => {
+      proxy.off("error", reject);
+      resolve();
+    });
+  });
 
   const address = proxy.address();
   if (!address) {
@@ -231,5 +258,5 @@ export const createAnthropicProxy = ({
   if (typeof address === "string") {
     return address;
   }
-  return `http://localhost:${address.port}`;
+  return `http://${host === "127.0.0.1" ? "localhost" : host}:${address.port}`;
 };
diff --git a/src/main.ts b/src/main.ts
index 9df7873..f8dfb08 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -6,6 +6,7 @@ import { createGoogleGenerativeAI } from "@ai-sdk/google";
 import { createOpenAI } from "@ai-sdk/openai";
 import { createXai } from "@ai-sdk/xai";
 import { spawn } from "child_process";
+import { randomUUID } from "crypto";
 import {
   createAnthropicProxy,
   type CreateAnthropicProxyOptions,
@@ -42,28 +43,60 @@ if (process.env.ANTHROPIC_API_KEY) {
   });
 }
 
-const proxyURL = createAnthropicProxy({
-  providers,
-});
+// Authentication token for the proxy. If the user already provided an
+// ANTHROPIC_AUTH_TOKEN or ANTHROPIC_API_KEY, reuse it so Claude sends it as
+// Authorization: Bearer / X-Api-Key. Otherwise generate an ephemeral token and
+// inject it only into the spawned Claude process.
+const proxyAuthToken =
+  process.env.ANTHROPIC_AUTH_TOKEN ??
+  process.env.ANTHROPIC_API_KEY ??
+  randomUUID();
+
+const proxyAuthHeaderName = process.env.ANYCLAUDE_AUTH_HEADER ?? "X-AnyClaude-Token";
+
+// Allow overriding host/port via environment variables for flexibility. If
+// port is not provided, we bind to an ephemeral random port for parallel safety.
+const proxyHost = process.env.ANYCLAUDE_HOST || "127.0.0.1";
+const proxyPort = process.env.ANYCLAUDE_PORT
+  ? Number(process.env.ANYCLAUDE_PORT)
+  : undefined;
+
+(async () => {
+  const proxyURL = await createAnthropicProxy({
+    providers,
+    host: proxyHost,
+    port: proxyPort,
+    authToken: proxyAuthToken,
+    authHeaderName: proxyAuthHeaderName,
+  });
+
+  if (process.env.PROXY_ONLY === "true") {
+    console.log("Proxy only mode: " + proxyURL);
+    return;
+  }
 
-if (process.env.PROXY_ONLY === "true") {
-  console.log("Proxy only mode: "+proxyURL);
-} else {
   const claudeArgs = process.argv.slice(2);
   const proc = spawn("claude", claudeArgs, {
     env: {
       ...process.env,
       ANTHROPIC_BASE_URL: proxyURL,
+      // Ensure the Claude CLI includes our custom header via ANTHROPIC_CUSTOM_HEADERS
+      ANTHROPIC_CUSTOM_HEADERS: (() => {
+        const existing = process.env.ANTHROPIC_CUSTOM_HEADERS;
+        const line = `${proxyAuthHeaderName}: ${proxyAuthToken}`;
+        return existing ? `${existing}\n${line}` : line;
+      })(),
     },
     stdio: "inherit",
   });
   proc.on("exit", (code) => {
     if (claudeArgs[0] === "-h" || claudeArgs[0] === "--help") {
-      console.log("\nCustom Models:")
-      console.log("  --model <provider>/<model>      e.g. openai/o3");
+      console.log("\nCustom Models:");
+      console.log("  --model <provider>/<model>      e.g. openai/gpt-5-mini");
     }
-
-    process.exit(code);
+    process.exit(code ?? 0);
   });
-}
-
+})().catch((err) => {
+  console.error(err);
+  process.exit(1);
+});