Earlier quoted context omitted.
I don't think gofmt assumes any width for tabs. It, prints `\t` for indentation, and that's all.
It has the -tabwidth option, defaulting to 8. I have yet to figure out what it's used for, but presumably there is some case where it is used for alignment.
It was only used when you invoked the other option to use spaces instead of tabs. Both options are now removed. gofmt doesn't care how wide your tabstops are.