Samsung just launched the Galaxy S20 series a few days ago, but you can already mosey over the Samsung website to grab the official kernel source. The Exynos variants popped up a few days ago, but now the Snapdragon variants are live as well. The open source code isn't going to do you much good if you're not a developer, but the result of making that code available might.
Developers can download the kernel source from Samsung's open source repository. There are separate downloads for the S20, S20+, and S20 Ultra, all of which are available in Exynos and Snapdragon variants. The models that end in "U" are Snapdragon, and the ones with "B" are Exynos. Each one is a few hundred megabytes.
With kernel source, developers can configure apps and services for Samsung's latest phones. You'll probably see some custom recoveries and software builds appear, and devs can optimize regular apps for the devices.