Systems, methods, and other embodiments associated with a phased release of a core application programming interface (API) are described. In one embodiment, a method includes performing a phased release to remote client devices to upgrade instances of a first core API to a second core API. The example method may also include deploying a facade API into instances of the first core API in response to determining that an API implementation relies upon functionality of the second core API. The facade API is a dummy interface for interacting with the API implementation in place of the functionality of the second core API. The example method may also include performing phased upgrades to upgrade subsets of the remote client devices in phases from the first core API to the second core API, where functionality of the second core API replaces the facade API.