Libraries
The API is plain HTTPS with JSON. Native libraries come later, TypeScript first.
Today
The API is plain HTTPS with JSON bodies, so any HTTP client can call it. The guides and the reference show each request as a curl command, which you can translate into the client your system already uses.
The OpenAPI file describes every operation. An OpenAPI code generator can produce a client from it.
To see a real answer before you write any code, use Test Request in the API reference, which reads fixture data on the demo deployment with the demo key.
Planned
Native libraries follow, TypeScript first. When one exists it is listed on this page, and the reference shows its samples beside curl.