I applied to the position through a recruiting agency. At first a recruiter contacted me and we had an 30 min phone screening/interview just to see if i was a good fit for the position. After deciding that I was they forwarded my resume to the project managers at twitter to see if they are interested. If the managers are interested then a in person interview at the Twitter HQ will be the next step. At the interview they asked about 10-15 common interview question and then gave me an written assessment. The interview took about 30-40 mins in total.