The link from the third party website that was posted on this thread on here says Smart Stick or Smart Box with voice search which suggests to me the 4K Smart box.
Where if you believe the NowTV Tweet posted by the NowTV Twitter Help Team they are quoting the NowTV stick plus all NowTV boxes apart from the first generation white box.
Suppose we will have to wait and see, but i doubt very much the white box will be compatible with the BT Sports App where it doesn't offer the full range of Apps from the NowTV Apps Store due to the lack of processing grunt being a first generation box.
All i would like to see now rolled out on the NowTV service sometime soon is the remaining eight Sky Sports channels getting the 50fps PQ treatment, a red button sports service, a 7 day sports catchup service and maybe a BT Sports App on my NowTV & Roku branded devices then i will be an happy NowTV customer
I suspect some of this will happen in the very near future except red button & 7 day catch up. FWIW I think now tv should provide this to monthly subscribers even if day week and mobile subscribers are excluded.
If it's similar to the Sky Sports Box Office or Netflix App then i would expect all NowTV branded devices will support the future BT Sports App (except the white NowTV box).
Though i have no insider knowledge about this, just pure speculation / guess work on my part.
Where is your source for BT passes on Now TV?
Currently it is only Ireland that has the BT sport pass on Now TV. Nothing yet for the UK market.
Direct from BT regarding BT sport month pass.
The BT Sport Monthly Pass allows you to watch through the BT Sport app on iOS, Android, Chromecast, Samsung Smart TV, Xbox One, Apple TV and Sony PlayStation 4. You can also watch online at sport.bt.com
Please note: you can't watch the BT Sport Monthly Pass on an Amazon Fire TV stick or a set-top box from any TV provider. This includes BT, Sky and Virgin