Today we updated our Xcode 9.0 beta 2 image to Xcode 9.0 beta 3 with the latest simulators.
You can use this image by specifying Xcode 9.0 in your circle.yml:
machine:
xcode:
version: "9.0"
This image tag will be automatically upgraded when new betas are released by Apple, until the final release of Xcode 9.