From The Dallas Morning News:

Southwest stated at its Investor Day it was planning a new (fourth) fare category but gave few details.

Current three fare categories:

https://www.dallasnews.com/business/airlines/2021/12/08/southwest-airlines-is-introducing-a-new-fare-type-heres-what-we-know-so-far/

In other news, Southwest intends to be profitable again in the fourth quarter:

https://www.reuters.com/business/aerospace-defense/southwest-expects-improvement-operating-revenue-growth-travel-recovers-2021-12-08/