Both models will be fabbed on TSMC's N6 node. The power envelope of these cards is said to be 107W and 53W, respectively. The Radeon RX 6500 XT is a dual-slot card that will need a 6-pin PCIe power connector. The Radeon RX 6400 on the other hand will be a single-slot, low-profile model that will draw all its current from the motherboard slot.
For its Navi 24 SKUs, AMD is introducing a new (marketing) specs metric, which is Memory Bandwidth with Infinity Cache. According to official specs, the RX 6500 XT has 232 GB/s and RX 6400 has 216 GB/s. Those figures without Infinity Cache would (probably) be 128 GB/s and 112 GB/s respectively. This also implies that RX 6500 XT has 16Gbps GDDR6 memory while RX 6400 comes with 14 Gbps modules.In terms of display connectors, both cards will get one DisplayPort and one HDMI port. The official reveal is expected during AMD's CES 2022 keynote. This event is scheduled for January 4th, 2022.