This is a really awkward sentence: "100% of our production system is now running Go as 95% of our application." I'm curious what the 5% is that they didn't convert to go.
Read the whole paragraph. It's C. "100% of our production system is now running Go as 95% of our application (C being the other bits). Not side bits, but our critical path."
Basically, once you are 95% Go, what parts are hard to convert to Go to make it 100%