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LineageOS now officially supports the Pixel 9 series
(9to5google.com)
This is a most excellent place for technology news and articles.
At that point using it will be less secure, the reason why GraphineOS stops supporting devices is because they focus on security. In addition the Pixel 9 will be EOL in what eight years from now? Maybe even more
Eight years, minus the few years you'd have to wait until the phone is close to affordable. And updates via LineageOS is still way better than just using a phone with no updates when it hits EOL like you normally would.