Is there any risk upgrading to Xcode 9 while working on projects to be released soon?

Question

I'm currently working on an app that is soon to be released. This would tend to push me to wait before upgrading to Xcode 9 beta just to make sure my environment is stable but ARKit is making me really curious and I'm thinking about updating asap :).

For those of you who are already the Xcode 9 Beta, are you experiencing any difficulties working on your previous projects?

That might be a trivial questions but I had issues in the past when updating Xcode, hence why I ask this time.

Answer 1

[edit]: it is now safe to upgrade to Xcode 9 (and Swift 3.2 or Swift 4) for releasing on iTunesConnect.

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[original message follows (when Xcode 9 was only a beta)]

iTunes Connect requires AppStore submissions to be done with a stable release of Xcode, so no, you can't upgrade safely yet for a release.

Currently, for the period June, July, August, early September 2017, you can use most (but not all) versions of Xcode between 6.0.1 and 8.3.3 for a submission to AppStore.

Likely, early-September 2017 will be opened to submissions from Xcode 9. And I bet that around January 2018 support for Xcode 6 will be dropped, keeping only the range Xcode7-Xcode9.

This does not impact TestFlight: you can already submit test builds from Xcode 9 beta to TestFlight.

So just keep multiple installations of Xcode by renaming the app eventually, so that you always keep a stable version available.

And don't upgrade your code to Swift 4 using a custom toolchain for submission with Xcode 8: iTunes Connect only accepts for submission Swift toolchains natively bundled with the Xcode you're using. Yet, you can eventually write code like:

#if swift(>=3.2)
    // for Xcode 9 beta
#else
    // for Xcode 8 and release on AppStore
#endif