This is a long interview process, so prepare to be patient. I completed 3 phone interviews and 1 in-person interview that consisted of a 30-minute shadow, 15-minute panel presentation + 30ish minutes of Q+A, and a 10-minute role play phone call. They will give you feedback throughout this entire process, make sure you ask for it at the end of each step.
1st interview: very basic, completed with a recruiter. Behavioral questions and STAR. I was informed of progression directly following the call.
2nd interview: building more on behavioral questions, with a different recruiter. I was informed directly after that I would be moving forward
3rd interview: this interview was done with two hiring managers. It was a little more in depth, and they answered follow up questions to my previous responses. I was informed within 3 days that I would be moving forward
4th interview: this was an on-site interview. They provided me with travel and arranged everything for me. The process was that I met with a current client partner for 30 minutes, then presented to two managers as well as my recruiter, then performed a mock phone call role play with one of the managers. I heard back two days later that I had gotten the job.
My advice for this entire process:
-Again, ask for feedback after each phone call and at the end of your panel AND after the role play call. Make sure you are taking note of this feedback and incorporating it into the interview process as you progress
-99% of this interview process is being able to answer behavioral questions in the STAR format. Go through GlassDoor, write down the questions people have provided and have 1-2 answers per question. It's okay to use the same examples throughout the process but make sure you stay consistent if you do that. Also, be mindful of the fact that the interviewers will be taking notes on your answers, so your next interviewer will be made aware of the examples you used in the past.
-Top three things they're looking on: proof of being a top performer (they love numbers/metrics so if you can, use those as early on as possible), collaborativeness, and being professional
Lastly, everyone at Gartner was SO nice. They want to help you and they want you to do well. If you put the work in and are prepared for each step and they deem you as a good fit, then you'll do just fine.