Assuming dependabot.

By default, Dependabot creates pull requests without automatically assigning any reviewers, so the correct number is zero. Reviewers can be configured explicitly through Dependabot configuration or assigned through repository mechanisms such as CODEOWNERS. GitHub recommends using appropriate ownership and review processes when particular teams should review dependency updates. This default differs from Dependabot's ability to create pull requests automatically: creating the update does not imply that a reviewer is selected automatically. A repository can customize Dependabot behavior through .github/dependabot.yml, including configuration related to update handling, but in the scenario specified there is no such configuration file. Consequently, no individual reviewer is automatically attached to the Dependabot pull request merely because Dependabot created it.