We have indeed just launched an adaptive ratings system on Brilliant. Levels still exist, except now instead of being determined by your performance over the past two weeks, your level is determined by your rating, which changes each time you solve or fail to solve a problem.
Read about levels and the new rating system here. You will note that the colors designating each level have changed as well. This was done to better capture the fact that levels on Brilliant are no longer sharply distinct things, but are more related along a continuum.
You can also link to an explanation of ratings, by clicking the "what's this?" link next to your rating on the problem solving page.
Remember while your levels are visible to everyone your rating in any given topic is visible only to you.
We hope this will help you gain more specific insight into your progress and how hard a particular problem is relative to your experience level. It will also help us better gauge the difficulty of the problems we distribute to you.
Let us know if you have any questions in this thread.