just got through the GitLab senior SWE loop in early 2026, and the system design round was genuinely different from what i prepared for. sharing notes because i couldn't find much specific info before going in.
there are two system design interviews in the final round. both are 60 minutes. the interviewers are engineers from the team you'd be joining, not random cross-org people, which matters a lot for the conversation.
what they actually asked me (paraphrased): design a CI/CD pipeline runner system that can handle bursty workloads at scale design the permissions/RBAC layer for a multi-tenant SaaS product
both were clearly GitLab-domain problems, not generic 'design Twitter' prompts. this is either very helpful (you can anchor on what you know about GitLab's actual product) or slightly tricky if you haven't used GitLab heavily. i had used it at work, which helped a ton.
what they cared about: tradeoffs. every decision needed a 'and here's why i'm NOT doing X instead' attached failure modes. what happens when a runner goes down mid-job? what's the blast radius? they pushed back constantly. not in a hostile way. more like 'what if your assumption is wrong here' every 10 minutes clarity on where you'd start. don't try to design everything. they want to see you scope
what they didn't care about: memorized textbook designs. one interviewer literally said 'forget the Designing Data-Intensive Applications answer, tell me what YOU would do first' deep Kubernetes internals (i expected more of this given GitLab's k8s-heavy stack, but it was more about logic than ops detail)
leveling note: for senior (roughly equivalent to L5 elsewhere) they seem to want you driving the conversation, not waiting for prompts. if you're going for staff they apparently raise the bar significantly on ambiguity handling and org-level thinking.
overall the system design portion felt more thoughtful than most loops i've done. less 'did you memorize the answer' and more 'can you think out loud with us.' prep accordingly.