This study aimed to examine transport layer API:s for the game development software Unity, and conclude its effect on latency. This effect was examined by conducting a controlled experiment, whereas three transport layer API:s, KCP, Telepathy, and Steamworks.NET were active on three different open-source Unity online games. The underlying network infrastructure Mirror was integrated to utilize each transport layer API, which also provided the components necessary to capture latency at runtime. In a second unstable connection experiment, the packet loss rate of 30% was configured to analyze the transport layer API:s performance during a poor connection. Although previous work has analyzed Mirror, the corresponding transport layer API within Mirror, and its effect on latency, have not been researched. The results suggest that Steamworks.NET achieves a significantly increased latency compared to KCP and Telepathy, though Telepathy only significantly increases from KCP under unstable network conditions.