Currently, we index the head of the default branch. However, the index format will support branch indexing, and we use that functionality to index forks, which

Currently, we index the head of the default branch. However, the index format will support branch indexing, and we use that functionality to index forks, which was not possible in prior incarnations of GitHub code search. Indexing specific commits (e.g., associated with a PR or feature branch) is on our roadmap.