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Setup guide

Use Claude Opus in Cursor without a US card

Add Claude Opus to Cursor as a custom OpenAI-compatible model on a ScaleMax key paid in rupees: the base URL, model ID, and what Cursor still runs itself.

5 minute readUpdated October 14, 2026By ScaleMax

Cursor can call any OpenAI-compatible endpoint as a custom model. That lets you run Claude Opus on a key you paid for in rupees with UPI: add a custom model with the ScaleMax base URL, paste the key, and type claude-opus-5-5. No US card is involved in paying for the model usage.

What you need

  • A ScaleMax key that includes Claude models — a Pay as you go key or a Claude token pack, bought with UPI, an Indian card or net banking on the pricing page.
  • Cursor installed and signed in.
  • The exact model ID you want. For Claude Opus 5.5 that is claude-opus-5-5; every ID is on the model list.

This covers the model usage bill. Cursor’s own plan, if you have one, is billed by Cursor.

Add Claude to Cursor

  1. Open Cursor Settings → Models and add a custom OpenAI-compatible model.
  2. Base URL: https://api.scalemax.pro/v1 for a Pay as you go key, or https://api.scalemax.pro/token/v1 for a token pack.
  3. API key: your full ScaleMax key.
  4. Model: claude-opus-5-5 (or claude-sonnet-5-5 for a cheaper, faster default).
Use the custom OpenAI-compatible form, not Cursor’s Anthropic login

Cursor’s built-in Anthropic option expects an Anthropic account. ScaleMax serves Claude over the OpenAI-compatible route for clients like Cursor, so the custom form is the one that works.

On macOS you can skip the manual steps: install the CLI with npm install -g scalemax@latest, run scalemax and choose Cursor. Run scalemax doctor again after Cursor updates.

Verify it works

Select the custom model in a chat and send Reply with K only. A single “K” means the base URL, key and model ID all line up. The request then shows in the request log of your ScaleMax dashboard, with its token count and cost.

What this does not change

  • Cursor support is experimental: an update can rename settings or reset a custom model. Re-check the three fields after upgrading.
  • ScaleMax answers the chat requests sent to your custom model. Cursor-owned features such as its autocomplete or background indexing may still run on Cursor’s own service.
  • Opus is a premium model. For routine edits, Sonnet or Haiku cost far less per token; compare them on the Opus 5.5 page.

Common problems

SymptomFix
Authentication errorThe key and base URL are from different billing modes. Token pack keys only work on /token/v1.
Model not foundThe key does not include Claude, or the ID has a typo. Check with GET /v1/models using the key.
The model disappearedA Cursor update reset it. Add it again, or re-run the installer on macOS.

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