For asynchronous languages like Node.js, Java, .NET, and Go, the tracking calls are asynchronous. Thereby, there's no significant impact on the latency when using such APIs.
For synchronous languages like PHP, Python, and Ruby, ~150 ms of latency is added to each such API call as these APIs send tracking calls from your server to the VWO server.
Note: For PHP, we have optimized our tracking approach for sending the calls which reduced the overall latency by one-third.