We recently announced upgraded ad extensions that provide many new capabilities, including mobile-optimized settings, new scheduling features, and detailed reporting at the individual sitelink level. We’ll be helping all advertisers transition to these improved extensions over the coming months. Starting on September 23, 2013, the AdWords API will support only these upgraded extensions, including the 25-character sitelink limit, and we’ll begin automatically upgrading legacy extensions to the new format.

We recommend upgrading your extensions ahead of September 23, 2013 so you can take advantage of all the new features and customize specific settings. Most advertisers are upgrading their extensions as part of their overall upgrade to AdWords enhanced campaigns. To help make the process easy for you, we’ve put together a number of resources:
As you are upgrading, you can create upgraded ad extensions while still keeping legacy ad extensions in the same campaign; however, only the upgraded extensions will be served. Beginning on September 23, if a campaign only has legacy extensions, we will auto-upgrade them to the new format. If a campaign has both legacy and upgraded extensions, we will only serve the new format, and legacy extensions will be marked as deleted.

If you have questions or need help with the upgrade, please visit us on the developer forum, or at one of the upcoming GDL Office Hours.