Kenya's tourism entry "revolution" will most likely have a transition period, in which both entry visas issued before December 31 and those issued close to the early days of 2024 will be valid, until at least as long as the evisa.go.ke website is still operational.
This is what we have learned, unofficially for now, from some local immigration sources. This could be three months or a little less, which is the time of validity of the online visa issued prior to travel.

It should be noted that the ETA will be cheaper (about 32.40 between fee and commission), although more information will be requested regarding travel, luggage and other information, so as soon as the site is operational, for now in the "test" phase (but someone has already managed to access and arrive at the payment) it will be convenient to do that.
Also note that the site itself suggests 72 hours as the timeframe for issuing travel authorization, so it will be wise to do that at least four days before departure, just in case.

ETA Kenya also recommends downloading the mobile app, also to always have your details entered.
More information will be forthcoming as we move forward, but unlikely in the coming holiday season.