This just in from the ubuntu-devel-annouce mailing list:

Most cycles, we have a week of breathing room where we can flip all the
switches in a coordinated fashion and open everything at exactly the
same time, but this archive opening sees various members of the release,
archive, and toolchain teams in transit all over the globe, so we'll
stagger things a bit.

In the next day or two, you should see a followup to this email from
Matthias Klose doing his usual announcement of what has changed in the
default toolchain, and Colin Watson turning on autosyncs from Debian.

Rather than wait until we're all awake at the same time, however, I'm
unfreezing the archive this morning and declaring Saucy open for active
development. Happy merging.

On behalf of the Release Team,

Adam Conrad