Some backends (see backends summary) support streaming bodies, as described by the Streams[S] capability. If that’s the case, you can set a stream of the supported type as a request body using the streamBody method, instead of the usual body method.


Here, streaming refers to (usually) non-blocking, asynchronous streams of data. To send data which is available as an InputStream, or a file from local storage (which is available as a File or Path), no special backend support is needed. See the documenttation on setting the request body.

An implementation of the Streams[S] capability must be passed to the .streamBody method, to determine the type of streams that are supported. These implementations are provided by the backend implementations, e.g. AkkaStreams or Fs2Streams[F].

For example, using the akka-http backend, a request with a streaming body can be defined as follows:

import sttp.client3._
import sttp.capabilities.akka.AkkaStreams

import akka.util.ByteString

val chunks = "Streaming test".getBytes("utf-8").grouped(10).to(Iterable)
val source: Source[ByteString, Any] = Source.apply(



A request with the body set as a stream can only be sent using a backend supporting exactly the given type of streams.

It’s also possible to specify that the response body should be a stream.