Like most Google apps, it's a staged rollout so you won't see it yet. It runs on at least Android 4.0+.

You can download and install the latest version from here if you don't want to wait: http://www.apkmirror.com/apk/google-inc/gmail/gmail-5-0-1556...

Answering my own question..

Will be available on the playstore in a few days. But can download it from Android Police here: http://www.androidpolice.com/2014/10/31/gmail-5-0-exchange-s...