It depends on the size of your project, but in my project it failed even though the full path was only 24 characters and I had to shorten it to 20 characters or less before it worked. So shorten it as much as you can and give it a try.
Also, as I mentioned above, this may be a bug in the xcode beta and I've reported it in the feedback.
jaden0
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@venturidoo
Including the scheme length, I've noticed that paths longer than 40 characters tend to cause failures, while paths up to 35 characters work fine. I suspect that this limit is somehow linked to the size of the project. For instance, when I removed several Swift files from my project, it was able to handle longer paths successfully.
In my case, which seems to be caused by the project path, the build succeeds in xcode beta3.