Could you explain how much improvement RL+fine tuning has given to Composer 2.0 over Kimi K2.5? I don't fully grasp the work Cursor model has done here and why

Could you explain how much improvement RL+fine tuning has given to Composer 2.0 over Kimi K2.5? I don't fully grasp the work Cursor model has done here and why it is difficult to achieve these results with RL.