There was a take home probability/combinatorics assessment followed by a technical interview with a mathematician employee and then a final behavioural + technical interview with the head of mathematics going over all aspects of the job and company.

After completing a few basic combinatorics problems, I was contacted by a HR rep about a potential video interview and was asked about my availability. I let them know when I was available and received a response five days later and was informed the hiring manager was busy. They asked to reschedule for the following week, so I agreed and asked what times were available. I heard no response until the day before. They scheduled me for a video interview without my confirmation and about 24 hours' notice. I hadn't even got the chance to confirm with them that I was available at this time or even on this day. So, I had to move things around to make myself available at this short notice. The interview it turns out was a technical interview asking about some more combinatorics problems without any discussion of my CV, asked to complete as many as I could in the half hour as soon as I was on camera. I completely underperformed at this stage and we left frustrated with myself and the HR rep for being unresponsive and unhelpful during the scheduling process. The next day that rep got back to me thanking me for my time with a person's name who wasn't the person who interviewed me. I was told that despite the interviewer being impressed with my experience (which didn't come up at all in the interview, I wasn't even asked for my name), other candidates were better suited to what they were looking for. The whole process felt like it wasn't being taken seriously and that I wasn't being taken seriously as a candidate.