HTTP/3 fixes head-of-line blocking that HTTP/2 introduced, but most apps will never feel the difference. The wins are concentrated in mobile, lossy networks, and CDN-served static assets. Here is the technical difference, the cases where it actually matters, and the cases where it doesn't.
Server-sent events are a 1.5KB drop-in for streaming notifications, progress, and live updates — and they work through every proxy and CDN that already handles HTTP. WebSockets are the right tool for genuine bidirectional, low-latency traffic. Here is the decision tree and the implementation patterns for each.
Most API developers think “HTTP caching” means putting things in Redis. The browser, the CDN, and your reverse proxy already implement a four-decade-old caching protocol — you just have to set the right headers. Here is the cheat-sheet of Cache-Control, ETag, Last-Modified, and the conditional-request flow that makes JSON endpoints feel instant.