G Research is a highly selective company that turns down plenty of people who would probably be good at the job, to make sure everyone who is hired is definitely very capable and a good fit. So the interview process was difficult, but at the same time I was always treated in a courteous and friendly way. No trick questions or mind games.
After sending a CV, I was invited to take a 90 minute test. See the website for details. I found out that I had passed that day. Over a few visits I sat several one on one technical interviews, maybe about an hour each, eventually meeting with senior management to assess how good a fit I would be, and I met with the team I would be joining. I was offered a very competitive salary, beyond what my recruiter had said was expected, no low offers or mind games, and accepted.