Update | The OnePlus 9 series can be purchased early through a German carrier
Update: Deutsche Telekom's latest OnePlus blind box offer is indeed now live. Hints as to its actual contents could be more specific: its new webpage just says that it has "the newest device" from the OEM, as well as many gadgets besides.
Unfortunately, it can't be purchased without also committing to a new tariff with the carrier, meaning its price ranges from ~€700 with a €70 monthly contract to €1 and €110 per month, plus a pre-order charge. In addition, it does not ship until March 24, 2021 - so no faster than "regular" zero-day OnePlus 9 orders, then.
The reliable tipster Max Jambor now claims that Deutsche Telekom and OnePlus will collaborate in order to offer a blind box for the upcoming 9 flagship phone series. The 2 companies did the same last year for the 8 series, suggesting there is at least some credence to this new leak.
Given the nature of this alleged event, it would seem the box in question would contain a 9-series device, possibly in addition to other contents such as accessories. However, there is no guarantee that something like a top-end 9 Pro would be among them - even despite the putative package's €1,111 (~US$1,325) price.
Similarly, should this sale start tomorrow (March 16, 2021) as claimed, this cost may not reflect the actual starting prices of the upcoming flagships. There are no hints of this offer on the Deutsche Telekom website to date.
Meanwhile, OnePlus has effectively confirmed the 9 Pro's design by previewing one of its new colorways, a "nature-inspired" gray-to-black gradient called Morning Mist; furthermore, there is now a teaser for the 9 in purple on its website.