It's been about a month since HTC said that the One M7 GPE's Android 5.1 update was coming soon, but better late than never, right? It appears that the rollout has begun and we've got your OTA download link below.
It's worth noting that the update is only 5.1, not 5.1.1. This is par for the course right now as no Nexus or GPE with a cellular radio has an official Android 5.1.1 build yet. This update is LMY47O just like the M8 GPE, and weighs in at about 280 MB. Remember, with the M7, you have to have S-OFF on your bootloader in order to manually flash OTAs in the stock recovery, so if you don't have that flag, you may need to just spam the "check now" button.