Announced 14 June 2017
We have a press release.
There is a information sheet
Broadcom says that the Trident3 has a unified buffer, unlike the segmented buffer of the Tomahawk. Buffer size is 32 MByte. The silicon geometry is 16 nm, same as the Trident2+. Best info so far is a PacketPushers blog posting. But you should read the post on their blog site to enjoy the fine discussion that follows.
The Trident3 has been designed with broadview fine grained performance monitoring in mind, so there's an information sheet on that. A sample look at a microburst as seen by the Trident3: