The actual update:
> ChromeOS devices will continue to receive regular updates and security patches through mid-2034. For qualifying devices purchased today whose 10-year support lifecycle extends beyond 2034, Google is committed to supporting your transition to Googlebook OS, with many devices offering direct migration paths.
In other words, support will be offered until 2034. if you're buying a new Chromebook today and intend to keep it for longer than 8 years, you're doing so at your own risk.