[jeroenhd]

Well-configured zstd can save a lot of bandwidth over gzip at this scale without major performance impact, especially with the custom dictionary. Initialising zstd with a custom dictionary also isn't very difficult for the client side.

As for application development, I think web socket APIs are generally exposed much better and used much easier than SSEs. I agree that SSEs are a more appropriate technology to use here, but they're used so little that I don't think the tooling is good. Just about every language has a dedicated websocket client library, but SSEs are usually implemented as a weird side effect of a HTTP connection you need to keep alive manually.

The stored ZSTD objects make sense, as you only need to compress once rather than compress for every stream (as the author details). It also helps store the data collected more efficiently on the server side if that's what you want to do.