[BUG] Claude Desktop – "Configure third-party inference" setup page fails with 503 (bootstrap request)

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Issue:
Opening the third-party inference setup page (app://localhost/setup-desktop-3p) always fails with "Unable to load
configuration". Log excerpt (custom3p-setup.log):
[bootstrap] Eager fetch failed: Bootstrap request failed: 503 Service Unavailable

Troubleshooting already performed (issue persists in every case):

1. Cleared Claude-3p profile cache (Cache, Code Cache, GPUCache, Dawn caches) — no config/credentials touched.
2. Confirmed app is on latest version (1.52386.0).
3. Found and fixed an unrelated OAuth issue (refresh token invalid_grant / session_stale_relogin) via full logout

("sign out of all devices") + fresh login. Auth now works correctly.

1. Despite a fully valid session and clean cache, the bootstrap call for setup-desktop-3p still returns 503 on every

attempt, across multiple days/sessions.

1. General network connectivity to Anthropic/claude.ai confirmed working (no proxy/firewall block detected).

What Should Happen?

Request:
Please check server-side status of the third-party-inference bootstrap endpoint, and confirm whether this account/org
is provisioned/entitled for this feature (the menu item is visible under Developer Mode, but the backend consistently
rejects the config fetch with 503).

Error Messages/Logs

[bootstrap] Eager fetch failed: Bootstrap request failed: 503 Service Unavailable

Steps to Reproduce

Steps to reproduce:

1. Open Claude Desktop (v1.52386.0, Windows 11).
2. Sign in normally with your Anthropic account.
3. Enable Developer Mode in Claude Desktop settings.
4. From the menu, open "Configure third-party inference".
5. The setup window opens at app://localhost/setup-desktop-3p.
6. The page fails to load and shows: "Unable to load configuration", with a toast: "Unable to update saved

configurations".

1. Clicking "Retry" reproduces the same error every time.

Expected result: the third-party inference configuration page loads normally.

Actual result: page fails to load; custom3p-setup.log shows:
[bootstrap] Eager fetch failed: Bootstrap request failed: 503 Service Unavailable

Additional notes:

• Reproducible 100% of the time, across multiple sessions/days.
• Persists after: clearing the app cache, confirming latest app version, and a full sign-out/sign-in (which did fix a

separate, unrelated OAuth invalid_grant issue found in the logs).

• General connectivity to claude.ai / Anthropic services is otherwise working fine.

Claude Model

Not sure / Multiple models

Is this a regression?

No, this never worked

Last Working Version

_No response_

Claude Code Version

Claude 1.52386.0 (1003ca) 2026-09-10T05:55:17.000Z

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Windows Terminal

Additional Information

_No response_