Wales coach Warren Gatland will have access to his Grand Slam winners for 13 days before their opener against Scotland at Murrayfield on 8 February after achieving player access he wanted for the RBS 6 Nations.
The major boost to Wales' hopes of retaining the Six Nations title comes after an agreement between the Welsh Rugby Union and the Welsh regions.
Wales also have first call on the players for the entire competition, even though there are two weekends of regional matches during the tournament.
The regions agreed to the terms after meetings at the start of this week.
England flanker James Haskell insists he will be pushing as hard as possible to be back from a toe injury in time to make his case for a spot in Eddie Jones' side looking to defend their RBS 6 Nations title next year.