We'll implant the stream here when it begins accessible so that it's less demanding to discover.
Upgrade: no livestream it appears to be, however here's a 12 minute announcment video.
Coincidentally, a few hours after the occasion is over, HTC will give us a chance to play with the 10 unit so we'll have direct impressions of the gadget later on. Read : Verizon Galaxy S6 edge+ gets Marshmallow, Note5 receives minor update