diff --git a/README.md b/README.md
index 0d36c13c..2a956656 100644
--- a/README.md
+++ b/README.md
@@ -154,6 +154,7 @@ The following command line options are available for the `start` command:
 | Option         | Description                                                                   | Default    | Alias |
 | -------------- | ----------------------------------------------------------------------------- | ---------- | ----- |
 | --port         | Port to listen on                                                             | 4141       | -p    |
+| --host         | Host/interface to listen on (e.g., 127.0.0.1 for IPv4, ::1 for IPv6)          | all (::)   | -h    |
 | --verbose      | Enable verbose logging                                                        | false      | -v    |
 | --account-type | Account type to use (individual, business, enterprise)                        | individual | -a    |
 | --manual       | Enable manual request approval                                                | false      | none  |
@@ -164,6 +165,24 @@ The following command line options are available for the `start` command:
 | --show-token   | Show GitHub and Copilot tokens on fetch and refresh                           | false      | none  |
 | --proxy-env    | Initialize proxy from environment variables                                   | false      | none  |
 
+ 
+#### Usage examples with --host
+ 
+Listen on IPv4 localhost only:
+```sh
+npx copilot-api@latest start --account-type business --host 127.0.0.1
+```
+ 
+Listen on IPv6 localhost only:
+```sh
+npx copilot-api@latest start --account-type business --host ::1
+```
+ 
+Default (listen on all interfaces):
+```sh
+npx copilot-api@latest start --account-type business
+```
+
 ### Auth Command Options
 
 | Option       | Description               | Default | Alias |
diff --git a/src/start.ts b/src/start.ts
index 14abbbdf..98307c2d 100644
--- a/src/start.ts
+++ b/src/start.ts
@@ -16,6 +16,7 @@ import { server } from "./server"
 
 interface RunServerOptions {
   port: number
+  host?: string
   verbose: boolean
   accountType: string
   manual: boolean
@@ -65,6 +66,7 @@ export async function runServer(options: RunServerOptions): Promise<void> {
   )
 
   const serverUrl = `http://localhost:${options.port}`
+  const hostForUrl = options.host || 'localhost';
 
   if (options.claudeCode) {
     invariant(state.models, "Models should be loaded by now")
@@ -117,6 +119,7 @@ export async function runServer(options: RunServerOptions): Promise<void> {
   serve({
     fetch: server.fetch as ServerHandler,
     port: options.port,
+    hostname: options.host || undefined, // undefined falls back to system default (all interfaces)
   })
 }
 
@@ -138,6 +141,12 @@ export const start = defineCommand({
       default: false,
       description: "Enable verbose logging",
     },
+    host: {
+      alias: "h",
+      type: "string",
+      description:
+        "Host/interface to listen on (e.g., 127.0.0.1 for IPv4 localhost, ::1 for IPv6 localhost)",
+    },
     "account-type": {
       alias: "a",
       type: "string",
@@ -193,6 +202,7 @@ export const start = defineCommand({
 
     return runServer({
       port: Number.parseInt(args.port, 10),
+      host: args.host,
       verbose: args.verbose,
       accountType: args["account-type"],
       manual: args.manual,