APIs are Application Programming Interfaces. APIs describe how one software application talks to another application. They are a published standard to allow programmers to write code to allow these applications to talk to each other.
Open Banking APIs cover the technical standards for how an application connects to your online or mobile bank account.
Open Banking APIs in the UK
Open Banking Ltd publishes the most commonly used Open Banking API standard in the UK. In order to support new requirements, it provides an evolving set of standards. As a result, different banks can be at different versions of the standards at any one time. Each bank can update if and when they see fit.
There are also different versions for dynamic registration of clients and security as well as optional elements to these standards.
Does everyone use the same API?
No. To add to the complication of different versions, not all banks follow this common standard. For example Starling have their own APIs standards and the Co-operative Bank has yet to adopt any formal standard.