Forum member Robpol86 has successfully managed to get Project Fi functioning on his Nexus 5, a service that should currently only function on the Nexus 6. This feat was made possible by activating the sim on a Nexus 6 first before transferring it to a Nexus 5 with a sim adapter.
The thread can be viewed here, and so far appears to be fully functional, although it remains to be seen whether in this instance the service continues to perform as it should or if this can be replicated on any Nexus 5 using the method provided. Whilst many previous attempts at transferring the service have not been successful, this could be due to the initial activation device used. It has now also been shown that a pre activated sim will not work on non Nexus hardware.
“I activated my Project Fi sim on a Nexus 6 and everything was working fine on it. Then I bought a nanosim-to-microsim adapter and put the activated Fi sim in my Nexus 5. I factory wiped my Nexus 5 since I like starting things off clean and setup my gmail account and other settings over WiFi. Then I installed the Project Fi app and opened it. The app activated Project Fi and gave me cell service. Everything so far seems to work fine on my Nexus 5.”