I don't know about your code, but in general, goroutine stacks are designed to start small and grow. There is nothing concerning about this. A call to runtime.newstack triggered by a large stack-allocated value would generally be cheaper than the corresponding heap allocation.

I found my issue, I was creating a 256 item fixed array of a 2*uint8 struct in my code. That was enough to cause newstack calls. It now went down from varying 10% to roughly 1%. Oddly enough it didn't change the ns/op a bit. I guess some mix of workload related irrelevancy and inaccurate reporting or another oversight on my side.