I'm a chip designer and a chip this complicated takes about 3 years from start to actual silicon so it would have started well before Softbank started their acquisition process of Ampere.
The press release says it was co-developed with Meta who has a growing custom chip team. Normally these chips like Amazon's Graviton or Google's Axion are designed for their own data center use only and rented to customers. This ARM chip sounds like Meta and other companies will all be able to buy chips for their own data centers.
I'm guessing Softbank will get ARM and Ampere to align on future chips or just merge Ampere completely into ARM.
I can only imagine that their boardroom minutes included heated exchanges between their legal and marketing teams.
V4 cores should be out this year using X925 and C1 Ultra-based V5 will probably be 2027-2028.
I suspect that X4 is already fast enough to beat EPYC in per-core performance when using the whole chip. ARM caught up/passed x86 in IPC all the way back around A77/78 in 2019-2020. They are now much faster per clock and hitting about the same all-core clockspeeds as standard EPYC (let alone zen5c EPYC).
The big issue is that Graviton5 is already starting to hit the market and uses the same v3 cores. A lot of marketshare for this chip will probably come from taking Ampere customers.