I'm going to give you the recruiter angle on this because I've prepped a few people for Twitter (X) loops and I've talked to enough people who went through it to have a real picture.
First, the format: they run one dedicated behavioral round, usually with a hiring manager or a senior IC on the panel. It's 45 minutes and it's not fluff. They have a structured rubric.
The questions they almost always ask, or close variants: Tell me about a time you disagreed strongly with a technical decision and what you did. Describe a project you drove from ambiguous idea to shipped product. A time you had to make a call with incomplete information. What was the decision, what did you miss? Tell me about the most critical production incident you've handled.
That last one comes up a lot. They're a company that has had very public outages and infra struggles. They want people who have real war stories from production. If you've never been on-call for anything real, that's a gap to think about.
What they're actually evaluating: This is post-acquisition Twitter. The culture skews toward ownership, speed, and not needing a lot of hand-holding. What they're really listening for is: do you default to asking permission or to making decisions? Do you clean up after yourself or do you hand-off and disappear? Did you actually lead the thing you're describing or just "contribute to" it?
"I was part of the team that" is a red flag to most interviewers there. Own the thing. You did it. You drove it.
Prep tip from someone who's watched this go wrong: STAR method is the baseline, but the story needs texture. The problem, the constraint you hit, what you tried first that didn't work, then the outcome. The texture is the signal. Generic clean success stories without friction read as rehearsed.
Comp context for behavioral pass: clearing the behavioral round and getting to HC felt pretty quick in the loops I've tracked, usually within a week of the last round. Calibration happens fast. If you don't hear back within 10 business days of the loop, it's probably not moving forward.