If you've found this page, you're likely on the right track to get the position, I think this is what helped me land the job myself!
The interview process was three-stage. First, a phone interview, then a demo interview, and finally video interviews with three of their Customer Support managers.
The phone interview was with a recruiter. My recruiter, Tony, was awesome. He was kind, communicated clearly, and was available if I ever had a question.
For the demo interview, they ask you to complete an activity inside of the HubSpot interface, talk about it, and then do a role play with a team lead. My advice for this part is, BE YOURSELF and relax. But, take it seriously. They want to see how you problem solve so if you don't nail it first try, that's okay, take a breath, course correct, and get it on the second try. Huge thanks to Gene for making me feel comfortable through the whole process!
Finally, the interviews with the three managers are 30 minutes each, back-to-back. A majority of the questions they ask will be behavioral, based on concrete examples from previous jobs.
My recommendation is to be yourself and do your research. Use the STAR method for responding to interviews, practice your answers ahead of time, and research your interviewers too (it's just as much about making sure the company is the right fit for you).
I will say, it was the most pleasant interview process I've been through, and although it was extensive and took about 4 weeks from start to finish, I've never felt more welcomed or calm. All of my interviewers we friendly and genuinely loved HubSpot and the culture of the company. I can't wait to be joining the team soon!