Doesn't seem like there's an official announcement since any news articles about it describe it as a "quietly discontinuing" [0]

I'm in the U.S. and a search for "oasis" has nothing but eye drops in its top results. You have to scroll down to find a listing for the "International Version — Kindle Oasis", selling at just $135 [1], but which Amazon refuses to ship if your address is in the U.S.

[0] https://www.thestreet.com/retail/amazon-quietly-discontinues...

[1] https://www.amazon.com/Kindle-Oasis-now-with-adjustable-warm...

The Verge asked Amazon, and they've said it's completely discontinued now:

https://www.theverge.com/2024/10/16/24272009/amazon-disconti...

As with all previous kindles, the only official bit is the removal from the store. There hasn't been a case (so far) of a kindle that was removed from the store and then a later model being released.