The first round was just a HackerRank. The second round consisted of two one-hour interviews back-to-back, and they were technical interviews (slightly harder than HackerRank).
Overall, the process took somewhere around 3-4 weeks, so it was pretty speedy.
HackerRank was focused on string parsing.
The following metrics were computed from 2 interview experiences for the Twilio SWE Intern role in United States.
Twilio's interview process for their SWE Intern roles in the United States is fairly selective, failing a large portion of engineers who go through it.
Candidates reported having very good feelings for Twilio's SWE Intern interview process in United States.