Remove 'Rate limit' from one sub domain

I have a subdomain that hold my API. (api.domain.com)
The API is NOT needed for Rate Limit and gets alot of requests (millions/month).
This shows in the Billing as the Rate Limit counts all requests.

If I cant remove the API subdomain I need to turn of RateLimit from my Account. To expensive.
This is bad because the main site needs this.

How can I exclude the API subdomain from Rate Limit?

Br,
Henrik