Google has made it possible to add sitelinks to ads at the account level. This is designed to save time by allowing advertisers to create sitelinks that can be displayed with any ad in their account.
This is in the process of being rolled out, meaning not all advertisers have access at the moment but they soon will. If you’re not currently utilizing sitelinks at a campaign or ad group level, then any future sitelinks added will be automatically created at the account level.
Using Account-Level Sitelink Extensions
When adding sitelinks at an account level you will be asked to provide the link text that will display in search results, and the URLs being linked to.
There will also be cases when Google decides to automatically use information in your AdWords account associated with individual sitelinks — such as other ads in your account that link to the same URLs.
When sitelink extensions are served on a computer or tablet, between 2 to 6 links can be displayed. When served on a mobile device up to 4 links will be displayed. Ads both at the top and bottom of Google search results can display sitelink extensions.
Sitelinks are free to add regardless of how many you create. You only pay for sitelinks when people click on them. The cost-per-click of a sitelink is the same as the cost of clicking the display URL of the same ad. However, you’ll never get charged for more than two clicks per ad impression. If someone were to quickly click multiple links on an ad, it will be treated as a duplicate or invalid click
For more information about sitelink extensions, see Google’s support document.