In Clinical Operations at least, Gilead has a 3 step process (though I've heard it can vary based on how urgent the hiring needs are).
1. Recruiter contact. Recruiter calls, emails you the job description to review, does a pre-screen. If all goes well, you get set up for a phone interview.
2. 30 minute phone interview - fairly general questions about your experience, why Gilead, answer any questions you have about the position, letting you know what type of personality they think it takes to succeed at Gilead.
3. If all goes well on the phone interview, they'll set up a half-day in person interview. The on-site interview is anywhere from 6-9 people who all will interview you for 30 minutes. It's basically the same 30 minute interview over and over, but with people at different levels in different TAs in Clin Ops. You'll get an agenda of the interviewers ahead of time, but don't be surprised if it changes on the day of the interview.
The interview process really is about 2 things, does your experience fit with the job you're applying for and if you have any deficiencies are they something you can learn fairly easily, but most of all the interview is about finding out where your personality will fit within Gilead. One thing that was emphasized to me during the interview process is that Gilead really tries to fit employees with managers that fit their work style.
I interviewed in the afternoon and heard from the recruiter that evening letting me know they were going to prepare an offer. I think that same day/next day outcome is pretty standard in Clin Ops as long as the key stakeholders are in the office, but I've heard that in other departments it can take much much longer.