GitHub is a development platform with code hosting, issue tracking, code review, and more. GitHub code search is the next iteration of GitHub’s native code search and navigation functionality that can be used to search code stored in GitHub. It’s currently in technical preview and is separate from GitHub’s primary UI (GitHub will eventually integrate this functionality into the primary UI).
Sourcegraph is a code intelligence platform that makes codebases intelligible by semantically indexing and analyzing all of an organization’s code, providing developers and engineering leaders with a complete understanding of their codebase. In addition to universal code search across every code host, Sourcegraph has features to help developers find code, understand and answer questions about code, and fix code faster.
View this detailed comparision within Sourcegraph Docs.