What is Lumia 1520 preview for developer update

[mrruz]

I installed the preview for developers app and it asked me that there was an update. I haven't downloaded it yet. Is it Denim?

If so, how does it work on the 1520? And do you think ill be able to update to official release, or windows 10?

Thanks

 

[alex athanasopoulos]

The pfd doesn't install firmware. My best guess is that your available update is 8.1 update 1.