GitHub has been encouraging all repositories to rename their default branch from master to main. See GitHub's explanation and tooling guide: https://github.com/github/renaming

Internal precedent:

• DOP-3949 — "Rename our primary branches to main" (closed/fixed): Establishes that "All DOP-managed repositories use main as their primary branch name."
• CSHARP-5197 — "Rename default branch to main": Documents how the C# driver completed this. Specifically: renamed the default GitHub branch to main and updated Evergreen configuration to match.

Steps to complete:

1. Rename the master branch to main on GitHub (GitHub's rename tool automatically retargets open PRs)
2. Set main as the default branch in repository settings
3. Update Evergreen project configuration to reference main instead of master
4. Audit any other CI, bot, or automation references to master (e.g. release scripts, .github/ workflows)
5. Update contributor documentation that mentions master