[BUG] CLI 401 OAuth errors. Multiple devices on two Pro accounts, fully paid.

Environment

• Platform (select one):
• [X] Anthropic API
• [ ] AWS Bedrock
• [ ] Google Vertex AI
• [ ] Other: <!-- specify -->
• Claude CLI version: v1.0.83
• Operating System: Windows 11 Pro, and Windows Server 2025. Both with latest version of Git Bash installed.
• Terminal: Happens everywhere: powershell, cmd, curser

Bug Description

On all devices, after successfully authenticating, I get the 401 API error that OAuth is not supported. Same result on different account.

API Error: 401 {"type":"error","error":{"type":"authentication_error","message":"OAuth authentication is
currently not supported."}}

<img width="1316" height="265" alt="Image" src="https://github.com/user-attachments/assets/a6ef5e62-41e6-4427-be5a-955a3e6a2806" />

All troubleshooting steps completed. logout/login. clear .claude. uninstall reinstall. multiple devices. multiple Pro accounts, both fully paid.

Steps to Reproduce

1. Run claude.ex
2. Select Pro authorization
3. Browser opens, complete authentication and authorization (using google sign in), successful
4. Return to cli screen, it says I have successfully authenticated (<img width="571" height="66" alt="Image" src="https://github.com/user-attachments/assets/a556ee42-1d86-4516-8c12-00968fc8f23e" />)
5. Hit enter through the warnings
6. At the chat prompt type "hello" and hit enter
7. The 401 error is the result

Expected Behavior

Claude responds in chat

Actual Behavior

Get API Error: 401 {"type":"error","error":{"type":"authentication_error","message":"OAuth authentication is
currently not supported."}}

Additional Context

If you are doing heavy work and hit the 5 hour timeout, when you return after the reset, you will get this error, and twice be able to fix it with a logout and login. On the third time, that wont worked and you are locked out. This exact pattern occurred on two different Claude Pro accounts.