If you want to update your ACME configuration to use these new 64-day certs now to get a head start on the transition... there's currently no way to do so.
LE for reasons unknown did not opt to use their "profile" capability to allow subscribers to select 64 day certs as an option. They mention that they will update their staging environment on 2026-10-14 to use 64 day lifetimes, presumably with the "classsic" profile although they do not specify. But the staging env is not useful if you need a valid browser-trusted cert.
LE for reasons unknown did not opt to use their "profile" capability to allow subscribers to select 64 day certs as an option. They mention that they will update their staging environment on 2026-10-14 to use 64 day lifetimes, presumably with the "classsic" profile although they do not specify. But the staging env is not useful if you need a valid browser-trusted cert.
https://letsencrypt.org/docs/profiles/
You can however use the "tlsserver" profile to jump straight to 45 day certs.
https://letsencrypt.org/docs/profiles/#tlsserver
Confusing decision not to create a profile to help smooth the transition.