Long and arduous but rewarding process. Four stage interview process starting with a phone screening with a recruiter (conversational) and a follow-up with the same recruiter which was more extensive than the first call (more STAR based question and feeling out your motives for the position).
The third interview is with a lead skills assessor to get an idea of your sales personality ending with a sales role play (discovery call, not a pitch so dont try to sell them anything). This interview is essentially to see how you communicate and if you have the sales mentality to do well on the job. Expect to get constant feedback from them throughout the process. If you want the job, be sure to take the feedback well and actually attempt to apply it further along the process (coach-ability is a very important component to advancing in the process).
The fourth and final interview is an Invitational Day at their Ft. Myers location that consists of a group elevator pitch interview (3-5 people plus panel of Gartner employees and managers), a 1:1 or 1:2 panel interview, a whiteboard presentation you will give to your interviewers where you will have to explain what Gartner does and how they help their clients (expect to be interrupted throughout with questions, don't compare Gartner to other companies, be objective and have examples ready), a catered lunch, several presentations about relocation, community service, a Q&A with current AMs and then a final sales role play (similar to the first role play but a bit longer and more extensive, again not a sales pitch so just uncover as much info as possible and be confident with your questions and don't try to dominate the call, actively listen to the responses on the call b/c they will be dropping breadcrumbs that you will need to pick up and you will be given the call info and instructions well in advance. I recommend researching "value selling" and some sales call techniques (i.e building rapport, asking open-ended questions,
The event ends with a facility tour while Gartner deliberates your fate followed by a ceremony that is extremely rewarding if you get an offer. You will know if you got one the same day.
Be yourself and leave it on all the table. If you make it to the invitational round just know the job is yours to lose (they are willing to hire everyone who is invited so don't think of it in terms of a competition with other applicants, you are your only competition). Remember, feedback is most important. If you cant tale criticism this isnt the job for you. Be prepared for a long but fun day