Tuesday, April 17th 2012
The bets are off, there indeed is a new installment to the Halo franchise in the works, called Halo 4. Its release date was announced to be "Holiday 2012", more specifically 6 November, 2012. Microsoft and 343 Industries confirmed this date on Tuesday. "Set in the aftermath of Halo 3, Master Chief returns to confront his own destiny and face an ancient evil that threatens the fate of the entire universe. Halo 4 marks the start of a new trilogy that begins with its release in 2012," an Overview page on Halo website reads.
Source: Official Xbox Magazine