Create a mocking service that replicates the backend system's production performance characteristics. Then configure the API implementation to use the mocking service and conduct the performance tests

Use MUnit to simulate standard responses from the backend system then conduct performance tests to identify other bottlenecks in the system

Include logic within the API implementation that bypasses invocations of the backend system in a performance test situation. Instead invoking local stubs that replicate typical backend system responses then conduct performance tests using this API Implementation

Conduct scaled-down performance tests in the staging environment against the rate limited backend system then upscale performance results to full production scale