The C9 League is a formal alliance of nine Chinese universities modeled loosely on the American Ivy League. It was announced in 2009 as part of the 985 project.
Members: Peking University, Tsinghua University, Fudan University, Shanghai Jiao Tong University, Zhejiang University, Nanjing University, University of Science and Technology of China, Harbin Institute of Technology, and Xi'an Jiaotong University.
Together the nine account for a very small fraction of national university enrollment — under 1% — but disproportionately large shares of research output, national grants, and prominent graduates.
Membership has been stable since 2009, though the more recent 双一流 designations have somewhat blurred the C9's exclusivity by elevating a broader set of universities and disciplines.
For most students, 'C9' is a useful shorthand for 'top-tier research university with national profile' and less useful as a strict admission target — the individual universities and their programs are what actually differ.