Provider Error 57 with Opus 4.6 after adding custom Anthropic API key

[yzaremba]

Where does the bug appear (feature/product)?

Cursor IDE

Describe the Bug

I ran out of tokens for premium models and tried adding my own Anthropic API key. Now, any request to Opus/Sonnet fail with Error 57. Other models seem to work ok and the key itself works with Anthropic directly.

Steps to Reproduce

Add a custom Anthropic key. Make a request using a specific model (Opus/Sonnet). Request fails with Error 57.

Expected Behavior

Request works and does not fail

Screenshots / Screen Recordings

Operating System

Windows 10/11

Version Information

Version: 2.4.37 (user setup)
VSCode Version: 1.105.1
Commit: 7b9c34466f5c119e93c3e654bb80fe9306b6cc70
Date: 2026-02-12T23:15:35.107Z
Build Type: Stable
Release Track: Default
Electron: 39.2.7
Chromium: 142.0.7444.235
Node.js: 22.21.1
V8: 14.2.231.21-electron.0
OS: Windows_NT x64 10.0.26100

For AI issues: which model did you use?

Opus 4.6

For AI issues: add Request ID with privacy disabled

d3136acd-b906-44ef-8559-4264fb4889cf

Additional Information

I have disabled all MCPs and reloaded/restarted Cursor. Did not make a difference.

Does this stop you from using Cursor

No - Cursor works, but with this issue

[Colin]

Hey there!

Anthropic is returning a message that your credit balance is too low to continue using the API key.

Your credit balance is too low to access the Anthropic API. Please go to Plans & Billing to upgrade or purchase credits.

You’ll need to make more credit available to that account/API key in order to use it.

[yzaremba]

Thank you for a quick response. I was getting the error with a completely fresh and working key. If you tested with my key just now (prior to 6pm EST), then ‘yes’, you are correct. The limit just got reset at 6pm EST, so if you want to verify, go ahead.

[Colin]

The screenshot you’re sharing doesn’t appear to be related to API keys. While Anthropic offers plans that include usage credits, this doesn’t mean you can use that credit with your own API keys. I’d suggest checking the following pages to see what’s available to you:

• API Keys | Claude Developer Platform (for API keys)
• Billing | Claude Developer Platform (for billing information)

[yzaremba]

You are absolutely correct. I verified with curl, this is my bad, thank you. Would have been really useful for the Provider Error 57 to include the text of the actual error from the provider.