Unfortunately Brahms was very much aware that posterity would have interest in the manuscripts to his works, since they are the first hand evidence of the creational process. Brahms did not want the public to have access to this - the music should speak for itself. Therefore he destroyed most of the sketches, first drafts and more substantial alterations.
Most of the surviving autographs are thus the fair copy for the publisher - the so called "Stichvorlage". However a few interesting autographs remain with both sketches, drafts and alterations - among others the manuscripts for the clarinet sonata op.120. and the German Requiem op.45.