Ever since Microsoft launched the Bing API a few years ago, this service was available for free to developers who wanted to use data from the company’s search engine in their own products. Today, however, Microsoft announced that it will soon start charging for access to the Bing Search API. The subscription price will start at around $40 per month and will include 20,000 queries. As part of this change, Microsoft will also start using its Windows Azure Marketplace to manage access to this service.

While Microsoft announced these general changes today, it did not release any specific information about the transition timeline and pricing structure for users who need more than 20,000 queries per month.

According to the Bing team, this change will give developers “access to fresher results, improved relevancy, and more opportunities to monetize their usage of the Search API.”

Until now, free access to its API gave Microsoft’s search engine a bit of a competitive advantage, as Google’s free custom search API only includes 100 queries per day.

It seems like charging for API access is becoming quite the trend among the major search players, though. Google, for example, also just started charging its high-volume users for access to its Maps API. Google’s Translate API, too, transitioned to a paid model late last year.