FWIW, I went to China last week, and sadly found out that Google Fi doesn't (yet?) support tethering while roaming on iOS. It's an annoying restriction; I worked around it with a local SOCKS5 proxy running on my iPhone, but I would have preferred not to have to hack around it at all.

To be fair, having an iPhone and Fi automatically makes me a bit of a second-class citizen with Fi, but hey, it's the cheapest way for me to have international roaming.