Microsoft has announced that it will begin charging for access to its Bing Search API, offering the services on a subscription model that starts at roughly $40 US per month for up to 20,000 queries. Microsoft says that the Bing Search API 2.0 will stay free during a transition period that may last several months, but after that, developers will have to pay up.

The subscriptions will be offered through the Windows Azure Marketplace, where developers can try the new version of the API for free right now. Microsoft says that details “regarding the transition timeline, pricing structure, and other changes will be announced in upcoming weeks.”

Microsoft says that, in order to offer fresher results, improved relevancy and “more opportunities to monetize” developer’s use of the API at scale, it will have to begin charging a monthly subscription fee.

Azure is an enormous product for Microsoft and this move shows that they are making an attempt to boost it by bringing a known product—Bing Search—into its fold. This should get more developers into the Azure mindset, offering a performance boost for current users of the API shows a direct benefit to moving to Azure. Also, moving the API over means that people using Azure, and not Bing, may be tempted to try it.

Our own Alex Wilhelm calls it “an effective cross-seeding between two huge investments.”

This also figures as a response to Amazon’s announcement that it would be launching a CloudSearch product that integrates in with AWS products. Microsoft does make some concessions towards those who may be using the API at a higher level, saying that “developers using approximately 3 to 4 million queries and above can expect to transition through a separate process.”

This is sure to be a controversial move for some heavy users of the API, but it does show that Microsoft is going ‘all-in’ on Azure, consolidating its APIs under the product.