This is a short summary of the future plans for Factorio.
Factorio 1.1 (stable since January 26 2021)
- The 1.1 release is the final release of the vanilla game.
- It will be maintained, so bugfixes, simple modding interface additions, or minor tweaks can happen, but that's about it. 
Factorio Expansion Pack
- The future plan is to release "one big expansion pack", see Friday Facts #365 - Future plans
- As of February 2022, development is on step 4 "Connecting systems into a prototype" out of 7 total steps until release. (Friday Facts #367 - Expansion news)