Starling Builder will support both Starling 1.x and 2.x for a long time. This guide will help you to migrate your project using Starling Builder from Starling 1.x to Starling 2.x without problems.
The engine is simple enough to support Starling 1.x and 2.x at the same time, so the latest engine master branch will always work for your project, no matter what version of Starling you are running.
The editor has to branch out to a different version for Starling 2.x. https://github.com/yuhengh/starling-builder-editor/tree/2.0 The layout data generated will be slightly different, due to API changes.
If you open a 1.x layout file using Starling Builder 2, the editor will prompt you to convert to 2.0 format. After your confirmation, the following conversion will occur
If you open a 2.x layout file using Starling Builder, the editor will prompt a newer format is detected and no conversion can occur.
The extensions also have to branch out to the different version. Checkout the 2.0 branch to make your own extension for Starling 2.x. https://github.com/yuhengh/starling-builder-extensions/tree/2.0