Several Months ago, Microsoft announced that the Bing Search API had moved to the Windows Azure Marketplace. This move would make the Bing Search API a paid service with a tiered structure. Developers had been given until August 1st, 2012 to transition to the new version of the Bing Search API.
Yesterday was August 1st and developers who have not made the necessary code changes will most likely find that their applications have stop returning results. Microsoft has sent out a reminder to developers:
"This is a reminder that the Bing Search API 2.0 will continue to be available until August 1, 2012. On and after this date, Bing Search API 2.0 AppIDs will no longer return results. We encourage you to sign up for our service on the Windows Azure Marketplace to continue using the API."
Developers need to transition their Bing Search API driven applications to the Windows Azure Marketplace as soon as possible. There is additional information about the transition on the new Bing Search API page.
At the time of this writing, the new tiered service structure for the Bing Search API offers "for up to 5,000 queries per month, developers can access the API for free." Queries totaling over 5,000 per month would incur costs based on the number of queries per month.