ByteArrayContent's ctor calls HttpContent.SetBuffer:

Which then allocates a MemoryStream:

This stream is not needed in the common case: if passing as a request content, it goes unused (or could be elided in other ways). It is only ever needed if the user calls GetStreamAsync() (or a few related ones) on their own content.

We should try to make this allocation only as needed, not every time. This also affects StringContent, which inherits from ByteArrayContent.