The term "onsite" is a bit misleading for AT&T now. Mine was fully virtual over Webex (not Zoom, not Google Meet, Webex. Be ready for Webex). Four sessions back to back with 10 minute breaks between them.
This was for a Staff/Principal-adjacent infrastructure engineering role at their network cloud division.
Session 1: Coding round 1 (45 min) One problem, medium complexity. Graph traversal variant. The interviewer was an SWE II who kept the environment calm. He told me explicitly to talk through my thinking before I coded, which I took seriously. The actual code was secondary; he was watching the problem-solving process.
Session 2: Coding round 2 (45 min) Another medium problem. This one involved interval merging. Felt like a classic LeetCode medium with a slight twist. I finished with time to spare and he asked me to consider optimizing memory usage afterward, which was a signal they think about practical constraints.
Session 3: System design (60 min) Long session. I was asked to design a content delivery system for AT&T TV (their streaming product). Interesting domain because it's not just serving files fast, it's also DRM, subscriber entitlement checks, and regional licensing. Lots of real-world nuance if you know the domain. I didn't know the streaming side well but I knew caching and CDN architecture and that got me through.
Session 4: Behavioral + hiring manager (45 min) The HM was a director level. Very conversational. Not a grilling. Asked about a time I drove consensus on a controversial technical decision. Asked about my approach to mentoring. Asked what I was looking for in a team. Ended with a clear "what questions do you have for me" and seemed genuinely interested in answering.
Overall feel: Professional and organized. The Webex tech hiccuped once in session 3 and the coordinator was responsive in getting us back on track. Less intense than Google or Amazon final rounds but not a rubber-stamp either.