NVIDIA's previous-gen GeForce RTX 4090 graphics card ships with 24GB of GDDR6X memory, but China being China, and we've got modded RTX 4090s with 48GB of VRAM being sold for $3400.

The custom-modded RTX 4090 has 48GB of GDDR6X memory and a custom AIO cooler, confirmed on Reddit by u/CeFurkan. The AIO cooler on the custom GeForce RTX 4090 has a triple-fan cooler attached to the radiator, with the retail packaging clearly showing "GeForce RTX 4090 48GB".
BYKSI makes the AIO cooler that you see on the modded RTX 4090 48GB graphics card, with the 48GB of memory seen in both Windows Task Manager as well as GPU-Z.

GPU-Z notes that it's the RTX 4090 with the AD102 GPU and 16384 CUDA cores, with its 48GB of GDDR6X memory on a 384-bit memory bus and just over 1TB/sec of memory bandwidth.
- Read more: RTX 4090 with upgraded 96GB VRAM teased: could release soon for AI workloads
- Read more: Chinese AI, cloud firms add VRAM to RTX 40 series GPUs: RTX 4090D with 48GB, RTX 4080 with 32GB
Now... if you're a gamer, you won't need a modded RTX 4090 with 48GB of VRAM... however, for AI workloads that additional VRAM is going to come in handy. You can see some more coverage of a custom RTX 4090D with 96GB (!!!) of VRAM in China, and an RTX 4080 with 32GB in the links above.

NVIDIA's new flagship Blackwell-based GeForce RTX 5090 ships with 32GB of newer GDDR7 memory, but the 48GB and 96GB versions of the RTX 4090 in China seem to be mega popular.