The changelog over on the develop branch of the SketchAPI is this:
"[Improved] The document from a library will now have a proper path (either local path or the appcast URL)",
"[New] Add support for Slices",
"[New] Add `exportFormats` property on Layer",
"[Improved] No need to specify the type when there is no choice (like Document.pages can only contain Pages, Layer.exportFormats can only contain ExportFormats, etc.)",
"[New] Add UI.getInputFromUser method and deprecate the other input methods",
"[New] Add some `getParent*` methods on Layer",
"[New] Add support for text styles",
"[New] Add some methods to store a session variable",
"[Improved] Allow using setting methods even from the Run Script panel",
"[New] Add method to get the theme of Sketch",
"[New] Add `background` property on Artboard",
"[New] Add `transform` property on Layer"
I've tested the new text styles successfully but the transform property isn't accessible yet. It's not clear what branch of the SketchAPI is shipped with the latest beta.