Valve has announced a new handheld system, the Steam Deck.
https://www.steamdeck.com/
It's an x86-64 system. It comes with Steam OS (currently based on Arch Linux) preinstalled, but you're able to install Windows to it if you want. Specs are:
CPU: Zen 2 4c/8t, 2.4-3.5GHz (up to 448 GFlops FP32)
GPU: 8 RDNA 2 CUs, 1.0-1.6GHz (up to 1.6 TFlops FP32)
RAM 16 GB LPDDR5 RAM (5500 MT/s)
Screen: 1280 x 800 @ 60Hz, 7 inches (17.78cm), touch
In addition to the standard gamepad control inputs, it also has two grip buttons per side (labelled R4, R5, L4, and L5) and two touchpads, which are upgrades from the kind on the Steam Controller, and a 6-axis gyro.
Also supports generic Bluetooth devices, unlike Sony's, Microsoft's, and Nintendo's systems. Which is handy because you can connect it to a TV with a dock.
There will be three models with different integrated storage options.
64GB eMMC @ $399
256GB NVMe @ $529
512GB NVMe @649 (also has an anti-glare etched glass screen)
Edit: There's also a MicroSD card slot for additional storage regardless of model.