Completed my Slack onsite for a senior infrastructure / platform role back in spring 2026. Five rounds across two days (virtual, Zoom). Here's the honest breakdown.
Round 1: Coding. 45 min, CoderPad, live interviewer. Got a medium-ish problem involving parsing structured data. Nothing exotic. Finished in 30 min and spent the rest discussing tradeoffs in my solution. Time complexity conversation followed.
Round 2: System Design. 60 min. Designing for scale, real-time-ish. For infra roles specifically they'll lean toward: distributed queues, storage systems, deployment topology questions. Very Slack-flavored: how do you handle message delivery guarantees at scale, how do you design for partial failures. More depth on the infra layer than a typical product-engineering system design.
Round 3: Behavioral 1. Cross-functional collaboration, conflict resolution, handling ambiguity. Standard STAR format but they probe hard on "what would you do differently." Read the room on length. Don't run 8 minutes on a single story.
Round 4: Behavioral 2. Focus on leadership and technical influence. "Tell me about a time you pushed a technical direction others were skeptical of." This is where senior candidates either shine or go flat.
Round 5: Hiring manager chat. 30 min. Not evaluative in the way the others are, but they're assessing fit and whether you're someone they'd actually want to work with. Ask good questions here. Show you've thought about what your first 90 days would look like.
Post-loop debrief was about a week. Heard back on a Friday afternoon, which I was not expecting.
Overall difficulty: harder than I expected for a non-FAANG company. Take it seriously.