Not necessarily? The type used for Response can include a "body" type that supports streaming. E.g., body: AsyncRead in Rust. In Go I think it would resemble a channel that emitted the contents of the body.
(As a library, though, you'd also want to make the simple non-streaming case of "just return this blob of bytes" simple for the consumer, too.)
(As a library, though, you'd also want to make the simple non-streaming case of "just return this blob of bytes" simple for the consumer, too.)