When I hear "cold start" I usually think of the amount of time between process exec to when my first line of code starts executing. In this case I would just assume that Rust will be faster since it's pretty much how long it takes to load the binary image into memory and jump to the _start/main entrypoint. Go has a whole runtime to boot up before ever getting to that point. Many, many layers of setup code. So it's not surprising at all that it has a significantly slower "cold boot".