It could be plastic. If it is, then it's a high quality plastic because I've been thinking it's glass this whole time. I've seen other users says it's glass as well.You sure it's tempered glass? Was it pre-installed?
I got my 3T mid-February, direct from OnePlus, US version. I came with a plastic screen protector already installed. I know for certain it's a plastic protector, as it's had some issues peeling away and bubbling at the bottom (near the home button).
Edit: yes, it was pre-installed.
