Spokesman Brandon LeBlanc announced that “Starting at 12:00 a.m. on October 18 in New Zealand (4:00 a.m. October 17 in Redmond, Wash.), Windows 8.1 will begin rolling out worldwide as a free update for consumers on Windows 8 through the Windows Store.”
No news yet as to whether Microsoft is planning to release the RTM update early to developers for feedback through MSDN and TechNet subscriptions.