ChipFlip
A last-generation card costing $3,628 more than the current generation's flagship is not how hardware pricing is supposed to work. The Gainward RTX 4090 sits at $8,378.70 used. The NVIDIA RTX 5090 sits at $4,750.00. Both are real listings.
The 4090's price is a supply story, not a performance one
The 5090 beats the 4090 on essentially every benchmark. It has more memory bandwidth, more cores, and a newer architecture. On raw capability this comparison isn't close.
What's happening to 4090 pricing is that production ended while demand from AI and workstation buyers didn't. A discontinued card that datacenter-adjacent buyers still want doesn't follow normal depreciation, and specific board-partner variants get squeezed hardest because the supply is thinnest.
Why a Gainward specifically
Gainward is a smaller partner with lower volume in North America. Fewer units shipped means fewer units on the secondhand market, and thin supply amplifies whatever the demand pressure is. You'll see the same effect on Palit and Inno3D variants of scarce cards.
That's a genuine flipping signal. When a card goes end-of-life, the low-volume partners' versions are the ones whose used prices move most.
What to actually do with this
If you're buying to game, this is straightforward: the 5090 is faster and $3,628 cheaper. There's no argument for the 4090 at these numbers.
If you're holding a 4090, the interesting read is that the market is currently paying you a premium to part with it, and that premium exists because of a supply condition that won't last forever once 5090 volume fully saturates.
Bottom line
Buy the 5090. It's faster, newer, and dramatically cheaper. The only people who should care about the 4090 listing are people who already own one, and what they should take from it is that now is an unusually good moment to sell.