An increase in the number of teams competing at the Rugby World Cup and a new Nations Championship have been announced by World Rugby.
The men's World Cup, which comes to its conclusion in France this weekend will be increased from 20 teams competing to 24 from the next edition in Australia in 2027.
A new biannual international Nations Championship involving the leading 12 northern and southern hemisphere sides will commence in 2026, along with a second division of 12 teams.
There will be promotion and relegation between the two divisions from 2030.
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"It is fitting that we finish Rugby World Cup 2023, the sport's greatest celebration of togetherness, with the sport's greatest feat of togetherness," World Rugby chairman Sir Bill Beaumont said of the announcement, which includes changes for the women's international game too.
"Agreement on the men's and women's global calendars and their content is the most significant development in the sport since the game went professional - a historic moment for our sport that sets us up collectively for success."
The Six Nations unions of England, Ireland, Scotland, Wales, France and Italy, plus the SANZAAR nations of South Africa, New Zealand, Australia and Argentina will all form part of the new Nations Championship top division. It will be played during the July and November international windows.
The remaining two places in the first division - previously reported as Fiji and Japan - will be decided by a process to be run by SANZAAR, while the planned second division will be run by World Rugby. The tournament is designed to provide certainty of fixtures for unions outside of existing international competitions.
The revised Rugby World Cup format will consist of six pools of four teams and will see the creation of a Round of 16 to take place before the quarter-finals.
The top two teams from each group will automatically qualify, as well as the best four third-placed teams.
Even though the number of sides is to be increased, the adjustment means the World Cup can be reduced from seven to six weeks from October 1 to November 13, 2027, while providing the same number of minimum rest days.
The draw for the next competition will take place in January 2026 in the hope of avoiding the lopsided groups seen in France over the last two months.
As part of the changes, the international window for November has been lifted from three to four weekends and the Six Nations will lose one of its fallow weeks.
It has yet to be decided which break week of the Six Nations will be removed but from 2026 the competition will be reduced from seven to six weeks to free up an international weekend for the Nations Cup in November.
"A new era is about to begin for our sport. An era that will bring certainty and opportunity for all," Beaumont said.
"An era that will support the many, not the few, and an era that will supercharge the development of the sport beyond its traditional and often self-imposed boundaries. All boats will rise together."
World Rugby's 51-member council voted on the changes on Tuesday but only just reached the required 75 per cent majority.
"Certain countries will have their own views on matters," Beaumont said. "I would like to think that around the room there might have been a few dissenters but on the whole there was a pretty significant vote in favour of these new competitions."
Criticism of the new format centres around not enough being done for less established nations, especially after the likes of Portugal and Uruguay have surpassed expectations at the World Cup, but World Rugby chief executive Alan Gilpin sees it as a radical improvement to the status quo.
"Is it perfect? Probably not. Is it a hell of a lot better than the current situation? Absolutely," Gilpin said.
The major change for the women's game, meanwhile, is the introduction of the first dedicated international release windows from 2026 as part of a global calendar for Test matches.
"We now look forward to an exciting new era for our sport commencing in 2026," Beaumont said.
"An era that will bring certainty and opportunity for all. An era that will support the many, not the few, and an era that will supercharge the development of the sport beyond its traditional and often self-imposed boundaries.
"I would like to thank all my colleagues for their spirit of collaboration. Today, we have achieved something special."