The reconstructions works (1.5 billion HUF) are challenging as the art deco style of the baths built in 1917 need to be preserved.
During the renovation period, the separate male and female thermal bath units were functioning in a co-ed style, but in a couple of weeks, you will not need to wear swimming costumes, the old apron system will come back.
Gellert Baths is coed on weekends (all pools), but during the weekdays, from Monday to Sunday, the thermal pools are men only and women only, while the standard pools with cool waters are open for all.
If it sounds confusing, it is. Gellert Baths is a huge palace of baths, so if in doubt, just ask your question in the comments.
After the second world war, there was not enough money to reconstruct more expensive art deco elements, so several details were simply replaced by cheaper socialist style solutions. The 2007-2008 baths reconstructions have brought back the glory of the 1917 Art Nouveau Gellert Baths. Enjoy!
By the way, Hotel Gellert is one of the top Budapest spa hotels, not the most exclusive or luxurious, but it will do for those who choose good value for money.
Photo by Istvan Huszti from Index.hu (http://index.hu/gal/?dir=0804/kult/gellert/)