Azure Active Directory (AD) B2C is for developers who want to build Web, PC and mobile apps apps and services that can authenticate with consumer identity services like Facebook, Google and (coming soon) Microsoft Account. And Azure AD B2B is for authenticating between business-to-business partners.
Azure AD B2B collaboration and B2C are based on what Microsoft already provides for employee identities with Azure AD. Today's new services expand these capabilities to external identities.
Azure AD B2C is available as a pay-as-you-go service for those who want to integrate it with their applications and services. The first 50,000 consumer identities are free, and after that developers pay "a fraction of a cent per authentication and per stored identity," according to a new Microsoft blog post about the new services.
Azure AD B2B is aimed at enabling businesses to share applications across companies without having to manage additional directories or partner identities. The B2B collaboration capabilities work with Azure AD Free, Azure AD Basic and Azure AD Premium, officials said. Pricing for AD B2B is here. The current B2C preview is free, but preview tenants are capped at 500,000 users.