We will have a CI outage for a couple of hours tomorrow starting at 11 Pacific, in order to upgrade the CI machines to the latest Xcode beta and SDKs. We’ll send out a message when the upgrade is complete.
As mentioned in the Swift 3.1 Release Process blog post, we have begun posting periodic snapshots for the swift-3.1-branch branch at: https://swift.org/download/#snapshots and will continue to post snapshots (if tests are passing) after the upgrade. The latest snapshot closely resembles the content of the Swift compiler in the beta, however, you may encounter issues (in place of the toolchain shipped in the beta itself) using it with Xcode because of SDK differences. The snapshot posted after we’ve upgraded CI and re-built with the beta SDKs should resolve any issues. The Xcode beta is available for download at: https://developer.apple.com/download/