One way is to look at your system as reported in SONOS. If the Connect is not in your system, I think all Gen 1’s have a blue rubber bottom whereas the Gen 2’s have a grey bottom.

Log in to https://www.sonos.com/myaccount/system/households/devices/ and see your devices listed. 

Right… But you might be purchasing on ebay say in which case you need something more practical to assess.

First 4 digits of the serial number are the YYMM of the manufacture date.  Anything 2016 and newer is Gen 2.  In fact, anecdotal evidence says the cutoff was 1502, or Feb. 2015.  

Well, some playbars are older...

So what?  We are talking about the Connect units, as specified in the original post and title of the thread.  We already know all Playbards are S2 compatible.  

Muchas Gracias por la respuesta Miguelito!! 

Thanks Miguelito!