I was lucky to get a pre-release version to test, and I decided to tear it down before I started trying it out. I posted this blog post with detailed pictures of the insides, and some more details and performance benchmarks: https://www.jeffgeerling.com/blog/2020/raspberry-pi-400-tear...
There are also a couple videos linked in the post, if you're more visually-inclined.
Fun fact: the Pi 400 (and Compute Module 4) both have newer revisions of the BCM2711 SoC (C0 instead of B0), and that's part of the reason the clock speed is higher on the Pi 400 (1.8 GHz) than on the regular Pi 4 model B (1.5 GHz)—the newer revision apparently handles faster clocks and scaling with less heat than the older revision.
There are also a couple videos linked in the post, if you're more visually-inclined.
Fun fact: the Pi 400 (and Compute Module 4) both have newer revisions of the BCM2711 SoC (C0 instead of B0), and that's part of the reason the clock speed is higher on the Pi 400 (1.8 GHz) than on the regular Pi 4 model B (1.5 GHz)—the newer revision apparently handles faster clocks and scaling with less heat than the older revision.