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.
Directly after the passage you quote:
> Google promised 10 years of updates for all Chromebooks, and it’s now breaking that promise for anyone buying a Chromebook between now and whenever the last Chromebook rolls off the production line
So, they're changing the promise from now on, and not breaking it for past users. Doesn't sound like they're breaking their promise to me.