There was an announcement of Preview 1 at " Announcing Flutter Release Preview 1 – Flutter – Medium"
Download the latest beta release of the Flutter SDK In the document. Get Started: Install on macOS - Flutter
Latest beta release version is 0.5.1. It's updated 2 months ago...
$ flutter upgrade
Flutter 0.5.1 • channel beta • https://github.com/flutter/flutter.git
Framework • revision c7ea3ca377 (9 weeks ago) • 2018-05-29 21:07:33 +0200
Engine • revision 1ed25ca7b7
Tools • Dart 2.0.0-dev.58.0.flutter-f981f09760
Latest master release version is 0.5.8-pre.163.
$ flutter channel master
$ flutter upgrade
Flutter 0.5.8-pre.163 • channel master • https://github.com/flutter/flutter.git
Framework • revision 29410abbe7 (2 days ago) • 2018-07-27 22:10:39 -0700
Engine • revision 72a38a6b13
Tools • Dart 2.0.0-dev.69.3.flutter-937ee2e8ca
Which channel do I use in Flutter SDK?
From the Flutter wiki:
Flutter has the following channels, in increasing order of stability:
master
The current tip-of-tree, absolute latest cutting edge build. Usually functional, though sometimes we accidentally break things.
dev (The dev channel was retired as of Flutter 2.8)
The latest fully-tested build. Usually functional, but see Bad Builds for a list of known "bad" dev builds. We continually try to roll master to dev. Doing so involves running many more tests than those that we run during master development, which is why this is not actually the same to master.
beta
Every month, we pick the "best" dev build of the previous month or so, and promote it to beta. These builds have been tested with our codelabs.
stable
When we believe we have a particularly good build, we promote it to the stable channel. We intend to do this more or less every quarter, but this may vary. We recommend that you use this channel for all production app releases. We may ship hotfixes to the stable channel for high-priority bugs, although our intent is to do this rarely.
So, use whichever channel you feel comfortable with, meets your needs and/or has whichever fixes in it you need. Start with stable and go from there.