Application form CV and cover letter.
Applied in September process took about 5 months. Heard back within the hour after the first round, took just over a week to get the offer through after the AC.
First round consisted of two 30 minute competency interviews with an associate and a vice president. Not technically difficult, usual competency questions, walk through cv, have a good answer as to why citi, and why s&t
Assessment centre took up an entire day
First task was a case study project (write a report and prepare a presentation, presented to a director with 10-15 mins of Q&A)
Then had to re-take the numeracy test
3 back to back interviews with directors, one seemed to concentrate entirely on your CV, another was a mixture of competency and technical questions, final one was fit/motivation
Finished the day with a group exercise, given some time to prepare and read through the literature, and then had a 30 minute group discussion where we had to agree on final outcomes