A short initial phone chat with the recruiter (who was excellent, even offering tips for the main interview).

Then, a technical phone interview with a developer.

The developer I spoke to was great; they seemed like a nice guy and managed to pose some tough technical questions without seeming combative.

They got back to me within a couple of days to let me know they wouldn't be taking it further.

Worked through a few coding questions using a shared document. The questions became progressively more complicated. We then went through a thought exercise regarding the limits of the proposed solution, considering constraints like bandwidth, CPU speed, and memory. We also discussed how performance could be improved without rewriting the basic algorithm.