[xx_ns]

To be fair, this is exactly what the Accept and Content-Type standard HTTP headers are for. Clients can tell the API "OK, send me application/json data instead of binary data" or vice versa. You can have the majority of your traffic (client traffic) using the binary format, and still support JSON for bot API usage. This is standardized for both WebSockets and HTTP.

[Spivak]

Is there a way to do this that doesn't require keeping two sets of books for every API? Because the JSON API is right now the canonical one and still has to work. I don't imagine the lift is worth it for the difference between compressed JSON and BSON.

Also how much can you realistically win when the payload for small messages where the difference matters are text?

[xx_ns]

Modern serialization libraries make supporting multiple serialization formats pretty transparent - of course, I'm not sure what the current situation is in Elixir land, which Discord seem to be using, but Go and Rust (as trivial examples) have serialization libraries which make serialization based on content negotiation pretty much transparent. Of course, this doesn't help with testing, you'll still need to be testing both content types separately, but the savings in bandwidth might just be worth it.

[_ahxg]

Moreover, i imagine a lot of these bots are built on top of an SDK instead of directly working with API calls, so would be just a matter of changing the SDK internals.

[tricked]

Websockets don't support headers per spec, discord gets around this by using a query paramater though.

[xx_ns]

The initial handshake request is still over regular HTTP, though, which is where I'd assume you'd want to agree upon which content type you'll be sending anyways.