All three parts, as well as the TRX40 chipset, will be announced on November 5th. Reviews and retail availability of the motherboards and Ryzen Threadripper 3960X and 3970X processors is expected on November 19th.
The Ryzen Threadripper 3990X flagship on the other hand will follow in January 2020:
On November 5th AMD will also announce Ryzen Threadripper 3990X processor. This model is currently planned for January 2020. In November AMD will only reveal the core count and the name of the CPU itself (it is clearly written in the document, in fact, it mentions “a teaser”). It is very likely that on November 5th the clock speeds will not be revealed.