Hyper supports sending HTTP/1.1 Chunked Trailer Fields as of v1.1.0. The http-body is now at v1.0 as well and uses frames to allow a stream to return data and trailers.

Hyper is designed to support streaming bodies. The current version of axum, v0.6, supports streaming a response. If we want to include trailers (sometimes called "trailing headers") then we need to implement our own custom body.