ChatGPT Desktop cannot authenticate through HTTP Basic proxy (407) while ChatGPT Classic works

What version of the Codex App are you using (From “About Codex” dialog)?

26.727.40816

What subscription do you have?

ChatGPT Plus

What platform is your computer?

Darwin 25.6.0 arm64 arm

What issue are you seeing?

Summary

The new ChatGPT Desktop application cannot be used behind an authenticated corporate HTTP proxy.

The previous ChatGPT Classic macOS application worked correctly in the exact same environment.

The new application fails before any conversation starts with:

DeviceCheck registration failed (407)

---

Environment

• macOS Tahoe 26.6
• Apple Silicon (M3 Pro)
• ChatGPT Plus
• Latest ChatGPT Desktop App
• Corporate proxy (Squid 5.9)

---

Proxy configuration

PAC file:

function FindProxyForURL(url, host) {
  host = host.toLowerCase();

  if (
      shExpMatch(host, "www.google.*") ||
      shExpMatch(host, "www.youtube.*") ||
      dnsDomainIs(host, "www.travelsmartsystems.com")
  ) {
      return "DIRECT";
  }

  return "PROXY proxy.clickandgo.com:5555";
}

The proxy requires HTTP Basic authentication.

Curl output:

HTTP/1.1 407 Proxy Authentication Required
Proxy-Authenticate: Basic realm="proxy"

---

Actual result

The application immediately fails with:

DeviceCheck registration failed (407)

The application never prompts for proxy credentials.

What steps can reproduce the bug?

1. Configure macOS to use the PAC file above.
2. The proxy requests HTTP Basic credentials.
3. Install the latest ChatGPT Desktop app.
4. Sign in.
5. Ask any question.

What is the expected behavior?

The application should either:

• prompt for HTTP Basic proxy credentials,
• reuse proxy credentials already stored by macOS,
• or support authenticated proxies like ChatGPT Classic did.

Additional information

Firefox works correctly because it prompts for proxy credentials.

The previous ChatGPT Classic application also worked correctly on the same Mac and same proxy configuration.

I also tested:

• HTTP_PROXY
• HTTPS_PROXY
• ALL_PROXY
• launchctl setenv

without success.

This looks like a regression introduced in the new ChatGPT Desktop application because the previous ChatGPT Classic app worked correctly behind the same authenticated proxy.