According to the “What’s New” panel in Duo admin, U2F is now available for the Duo Free tier:
Support for U2F Tokens has graduated from Labs features and is now a part of Duo Free and Duo MFA by default, in addition to Duo Access and Duo Beyond.
However, I cannot get it to work. I do not have any options in Settings related to Authentication Methods (i.e., no option to enable U2F as described here) and when I go to enroll a new user, I only have Mobile Phone, Tablet, and Landline as options on the enrollment screen. What do I need to do to have the U2F option on Duo Free? Thanks!