We have made API documentation available for the public APIs here. In addition, the code itself contains full documentation for the private APIs if you want to study the internals.
We have a list of FAQs that detail some of the changes and provide information about the new SDK.
We are maintaining a changelog as we update the SDK. Since this is an Beta SDK, we might need to break compatibility between releases if the need arises.
We are working hard to ensure your experience using the SDK is stable. In order to keep us nimble and allow us to bring you new functionality, without compromising on stability, we have ensured full test coverage of the new SDK. We are including this in the open source repository to assure you of our commitment to quality, but also with the hopes that you will contribute back to help keep it stable. The easiest way to do so is to file bugs and include a test case.