Sync API works on top of Delivery API. Sync requests for changes in published and unpublished content, i.e., Delivery API and Delivery Preview API, count towards the overall API Calls limit set in our Fair Use Policy or your subscription plan.There is no limit on the total number of API calls you can make.
Rate limitation
Rate limits specify the number of requests you can make to Sync API within a specific time window.For cached requests served from our CDN, we don't enforce any rate limits. These are repeated requests for cached data.For uncached requests that reach Sync API, we enforce a rate limitation of 100 requests per second and 2000 requests per minute. These are unique requests for uncached data.When you reach the rate limit, the API rejects the request and responds with a 429 HTTP error. This error comes with the Retry-After header that tells you how many seconds you need to wait before retrying your request. Each failed request is perfectly safe to retry. If you begin to receive 429 errors, reduce the frequency of your requests.
CDN-level protection
Additionally, a CDN-level protective layer is also in place by Fastly to filter out disruptive traffic before it reaches the API. These limitations are significantly higher and don't affect normal usage or cached content:
or your subscription plan.
There is no limit on the total number of API calls you can make.