PSD2, the European regulations for Open Banking, is designed to allow a more open and competitive Financial Services sector across the EU. There are pages and pages of information on managing the market, allowing companies large and small to compete, and the Security / Strong Authentication required to allow 3rd parties open access to banking APIs.
The thing is, these APIs have been effectively in the open for years.
Mobile Apps and other software have been communicating via APIs for some years now. Major enterprises across multiple markets have found the principle of the API to be useful in creating new networks and new value with the APIs being the conduits (and the glue) that brings them together. Many enterprises have freed their developers’ creativity and the product teams have been able to diversify and thrive as rarely before.