We have released a new version of our macOS build image with Xcode 9.1 build version
9B55. You can select Xcode 9.1 in your builds by adding the following to your
machine: xcode: version: "9.1"
The release notes from Apple are here:
All changes in the image are listed here: https://github.com/circleci/macos-image-tests/pull/19/files
The notable changes are: the iOS SDK is now version 11.1 rather than 11.0.1 (this is the version that Xcode 9.1 installs). Also bundle and node have all been bumped to the latest minor releases.
Please let us know if you have any questions or feedback.