It looks like the sponsor can choose (via a 'no forking' option) whether they are happy with patches to fix the issue or if they require them to be committed up

It looks like the sponsor can choose (via a 'no forking' option) whether they are happy with patches to fix the issue or if they require them to be committed upstream. It's an important distinction because there can be a lot of extra effort in going from "patches good enough to fix the case I care about" and "sufficiently general and well-engineered solution to get through code review and be committed upstream". Presumably you wouldn't take on trying to fulfil a bounty with the 'no forking' option set unless you were sufficiently familiar with the upstream community for the project to know that you had a reasonably good chance of getting your change committed. (That doesn't require that you have commit privileges, of course. Conversely, even if you do have direct commit access that doesn't necessarily mean you'll be able to get any old rubbish upstream without going through the same code review process as a non-committer.)