Alkass Digital
World Rugby has announced a new competition starting in 2026 as part of a "significant overhaul" of the men's international calendar.
The tournament will be made up of 24 teams, split into two divisions with 12 teams in each, with promotion and relegation starting from 2030.
The top division will include the 10 sides from the Six Nations and Rugby Championship, plus two unnamed others.
The World Cup will also be expanded to 24 teams from 2027.
Although there will be four additional nations taking part in Australia and a round of 16 will be created, the adjustments mean the next World Cup will last six weeks rather than seven, while the draw will be made in January 2026.
The 2023 pools were drawn in December 2020 and seedings based on world rankings from the start of that year, as some sides had not played during 2020 because of the Covid pandemic.
However, the top five ranked nations by the start of the event were situated in one half of the draw and three of those top five - Ireland, South Africa and Scotland - were all in the same pool.
The future changes have been announced four days before the winners of the Rugby World Cup will be crowned, with New Zealand facing South Africa in the final in Paris on Saturday.
Meanwhile, reforms to the women's game mean there will be no overlap between international and club fixtures for the first time from 2026.
Gilpin reflects on 'historic day'
The newly created competition - yet to be given an official name - will be played in July and November, replacing the current summer and autumn international windows.
It will take place in alternate years, excluding those which include the World Cup and British and Irish Lions tours.
Teams confirmed to be participating in the top division of the new global competition are the six which compete in the annual Six Nations tournament in Europe - England, Scotland, Wales, Ireland, France and Italy - as well as South Africa, New Zealand, Australia and Argentina, who contest the southern hemisphere's Rugby Championship.
The two unnamed others are most likely to be Fiji and Japan, ranked 10th and 12th in the world respectively.
Speaking to BBC Sport, World Rugby chief executive Alan Gilpin said: "I think it's really significant.
"We've had many years of trying to get to a position where we've created guaranteed pathways for all nations in men's and women's rugby, from wherever they are in regional competitions to global pinnacle events.
"This provides those opportunities, so it's a really historic day."
'Significant uplift' in games for tier-two nations
World Rugby said in its statement that the revamped calendar will provide a "significant uplift" in the number of matches for lower-ranked teams, known as "tier two" sides, against more established nations.
Speaking earlier this month at the end of the Rugby World Cup pool phase, World Rugby chairman Sir Bill Beaumont said the governing body "must, and will, do everything we can to provide greater certainty and opportunity of regular high-level competition" for those nations.
Fiji were the only tier-two side to qualify for the last eight, and there were mixed fortunes for the other teams competing in France.
Portugal upset Fiji to earn their first win at a World Cup and put in creditable performances against higher-ranked opposition, as did other nations including Uruguay and Samoa.
But Romania conceded more than 70 points in three of their four pool games, while Namibia and debutants Chile were also on the wrong end of heavy defeats.
Several players and coaches emphasised that a lack of regular top-level matches is unhelpful for tier-two sides, although the Covid pandemic was also a factor in a reduced number of fixtures for some emerging nations during the four-year cycle.
Analysis
BBC rugby union correspondent Chris Jones
This new calendar will see Fiji and Japan officially join the top table of world rugby, I understand, and while they won't be part of the Rugby Championship - which remains untouched alongside the Six Nations - they will be part of the new competition.
Each country will play at least six matches in the new tournament, meaning England, Scotland, Wales and Ireland could for example face New Zealand, Australia, South Africa, Argentina, Fiji and Japan, with three matches on tour in the summer and three at home in the autumn, with a Grand Final at the end of November to determine a winner.
This will give those fixtures a welcomed extra edge and narrative, but will see the end of traditional three-Test tours.
While there has been some criticism that the emerging nations will be shut out by today's news, World Rugby say there will be regular matches between tier one and emerging nations during Lions and World Cup years.
It's a tricky balance. Do emerging nations improve by playing sporadic matches against stronger opposition, as per the status quo? Or is it better for them to have guaranteed matches as part of regular competition, and a chance to grow from a solid base?
World Rugby is banking on it being the latter.
And while some emerging nations have voted against the new structure - Rugby Europe for example - it is understood there was also enough support from both unions and regional bodies outside the elite, with the motion passing by 41 votes to 10.