You must be a paying Cursor customer to use any external LLM such as Sonnet-4.
The attached image is what you will see if you have not updated your Cursor Subscription.
I don’t mind paying, I just don’t like how I’m having to find all of this out.
Note to CURSOR:
HEY CURSOR, If you need a UX Dsigner, I’m good to go… I could help you with business strategy. You need it!!!
---------- > UPDATE:
Limitations:
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Custom API keys only work with standard models from supported providers.
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Cursor does not support custom local LLMs or non-standard API formats natively. Workarounds exist for running local LLMs, but these are not officially supported and require exposing your local model as a compatible API endpoint
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.
Summary Table
| Feature | Free Version + API Key | Paid Version (Cursor Pro) |
|---|---|---|
| Use external LLM API key | Yes | Yes |
| Access advanced Cursor features | No (some features require Pro or specific models) | Yes (full access) |
| Supported providers | OpenAI, Anthropic, Google, Azure, AWS Bedrock, DeepSeek | Same |
| Local LLM support | Not natively supported | Not natively supported |
Conclusion:
Cursor IDE requires you to have tokens (credits) with Cursor to use Anthropic models—even if you provide your own paid Anthropic API key—due to a policy change that restricts Anthropic model access on the free plan. This is confirmed by multiple user reports and forum discussions: when you enter your Anthropic API key on the free plan, Cursor displays a message indicating that you need Cursor tokens or a Pro subscription to use Anthropic models
.