Design a News Feed

That framing comes from a candidate account and it is not the social one. There is no follower graph here. Publishers push items in continuously, readers have declared interests, and the system decides who sees what. Building the Twitter timeline you rehearsed will answer a question nobody asked.

The difference moves the hard part. In a social feed the difficulty is the follower graph and its celebrities. Here it is matching a continuous stream of arrivals against millions of interest profiles, fast enough that a reader opening the app sees something current.

Assume ten million readers, of whom perhaps one in ten is active on a given day. Items arrive at around five hundred per second across all sources. A reader opens their feed a handful of times daily, putting feed reads somewhere near thirty thousand per second at peak.