Since launching Google Apps Marketplace, "we've been working on billing API, which's based on Google Checkout. The API goal is to make it easy for Marketplace vendors to sell their installable app to Apps customers, using either a subscription model or one-time payment, and accommodating both free trial and freemium pricing plans. We're excited to get it in to developers' hands. Our current plan is to release it in Q4 for US sellers, and then expand to other seller countries," informs Google.
"As a reminder, Marketplace payment policy launched with a revenue sharing exemption period, which lasts until 3 months after the release of these billing APIs. Upon expiration, all installable apps sold through Marketplace are required to integrate with billing APIs and bill new customers acquired through Marketplace exclusively through these APIs," added Google.