But does "we partnered with Nitrokey" mean it is a Nitrokey that does? I couldn't tell.
You know what: it looks like I'm wrong; the product comparison page for Nitrokey says the pro doesn't do U2F; only their FIDO U2F key (which uses a less capable processor that doesn't do OpenPGP) does.
The nitrokey u2f is a third party product. I don't think any of their products support u2f yet.