Airport CEO's first public build was released in early access on the 28th of September 2017 at 19:00 CEST on Steam
Airport CEO's Beta 1.0 save was released on the 9th of September 2020 on the experimental branch, and is expected to come to the default branch in approximately two weeks.
Airport CEO is still an early access game. At this moment, there is no set release date for a "1.0" build.
Development Blogs are the best source for any updates.