Status: ML team lead @ large non-FAANG company (non-US).
YOE: 5.5

Had a prior interview cycle w/Facebook but was offered lower level (IC5) and rejected.

Phone

Skipped - they accepted the onsite round from the previous cycle.

Onsite (virtual)

Initial schedule: 2 coding, 2 ML architecture, 1 technical leadership.
Follow-up: 1 project retrospective, 1 management (to decide between M and IC branches)

Coding 1:

1. https://leetcode.com/problems/maximum-width-of-binary-tree/ - Maintaining level-wise map of left- and rightmost nodes' widths. Update via BFS while maintaining parent height, width and inheritance direction (left/right).
2. Won't say I'm 100% sure of all the details but something very closely resembling https://leetcode.com/problems/shortest-path-in-binary-matrix/ . Solved using BFS. Discussed why this is optimal and general case Dijkstra is not necessary.

Coding 2:

1. Given a set of currency pairs with associated exchange rates, and a start and destination currencies, find the minimum required number of conversions to get from start to destination (not the best exchange rate path!). Solved via BFS. Follow-up: for this optimal exchange path, also find the associated total exchange rate (simply multiply rates along the path).
2. https://leetcode.com/problems/minimum-window-substring/ - took some time to come up with that but solved essentialy with the same solution described in LC (via two pointers). Made a small bug in the process, fixed it after a notice from the interviewer.

ML architecture 1:
Design an ML system to recommend POIs to users (e.g. shops/bars/restaurants etc) that would, e.g., be intergrated into FB's feed.
Discussed general solution framework (candidate selection/main ranking/reranking-filtering), various ideas for these pipeline parts, features for ranking.

ML architecture 2:
Build a model to classify e-commerce goods into a large hierarchical category tree. Again, pretty standard ML case study, nothing too hard provided you've got ML experience.

Technical leadership:
Nothing outside the scope of a standard behavioural interview. Asked an example of a project that I did and how I helped my team succeed - I've got several real-life stories of my team doing good projects, so all preparation I had to do was to just refresh all the details of one particular project in my mind. Asked some follow-up questions on whether I had to solve conflicts, assist people's growth etc.

Project retrospective:
Discussed the same case as above. Dived into more detail on technical solutions, plus delved into project management territory (team ceremonies? Agile/scrum/etc?). Again, easy provided you've got something to tell.

Management:
This one, I felt, went poorly. Questions were very broad and general (e.g. "how do you assist your teammates' growth?"), and I felt like my answers (which I came up with on the spot, without doing much practice) didn't really "click" with the interviewer. If one were to prepare more seriously for this round, I would recommend going through a list of actual FAANG managerial interview questions (I would imagine there's not too many possible questions) and actually rehearsing answers.

After 1-2 weeks recruiter reached out with the decision that they are ready to proceed with IC6 and not M1.
Notably, at IC6 you don't get to choose your team after bootcamp, rather you go through team matching before you accept the offer. Went through 5 team matching sessions before accepting.