i totally missed this comment! i guess it was 27 days ago.
it is a little atypical to have a jam where the theme isn't revealed at the start, however, the first game jams i did were the 7-day-roguelikes and those are themeless. it's just a very useful constraint to set aside 1 week to execute some idea yo'uve been stewing on or generate some new idea in that time window.