Now that a new generation of consoles has arrived, the old ones have to make way and Sony is apparently fast-tracking this process. As reported by Japanese publication GameWatch, production of "most of the PS4 Slim (CUH-2000 series) and all PS4 Pro (CUH-7000 series) models" has been discontinued in Japan. The only model that will still be produced is the standard PS4 Jet Black 500GB Slim model. This can be seen from the Japanese PlayStation website where only the PS4 Slim can be seen under the "Main Unit Lineup", even if both Slim and Pro models show up on the PS4 page (however, I could not get the link to the "Main Unit Lineup" to work myself).
The GameWatch report notes that this discontinuation will allow the company to focus on the production of PS5 units which experienced shortages. This discontinuation news apparently applies only to Japan for now, with no news regarding whether western markets will follow suit.