It's going to be a dramatic departure from what fans are used to, so here's a full breakdown of what this means for football's top club competition.
Why is this all happening?
More games equals more money, and the biggest clubs always take a larger slice of the broadcasting revenues. The top teams also want to play more meaningful games against their main rivals, which this should create at an earlier stage of the Champions League.
So does this mean more games?
Under the original plan proposed in 2021, the tournament was to almost double in size, from a total of 125 games to 225, with each team playing 10 games in the group stage.
However, that has now been scaled back to eight group stage fixtures, meaning a total of 189 games in the season.
It means two extra matchdays will be needed for the Champions League group stage.
So what is the 'Swiss model'?
Rather than teams being drawn into eight groups of four, as is the case now, all clubs are placed into one giant table based on points, and then goal difference.
It is based on the Swiss-system tournament used in chess, whereby each team does not play all of the others. The key difference is the chess format decides a team's next opponents after each set of games, whereas in the Champions League all group-stage fixtures will be known at the start of the season.
It has been used in football in other competitions with a large number of participants, including in the CONCACAF Nations League qualifying competition where all teams played four matches but the results were fed into one league of 34 nations.
How many teams will be in the new Champions League?
The number of clubs will be raised from 32 to 36. The new format means teams are guaranteed a minimum of eight games, and most will play at least 10.
Where do the 4 extra teams come from?
1) The third-placed team of the league ranked fifth by UEFA will go direct to the group stage (at present, that club must play two qualifying rounds). Historically that has almost always been France. Based upon league positions as of May 11 this season, AS Monaco would be promoted to the UCL group stage. Ligue 1's place in the qualifying rounds would drop to fourth in the league, if so Rennes would be elevated from the Europa League (UEL) on current positions.
2) An additional team via the "Champions Path" qualifying route, which features the leagues ranked outside the top 10 in the UEFA Country Coefficient. To give an idea of who could benefit, the losing clubs in the final qualifying round this season were Brondby, Dinamo Zagreb, Ferencvaros and Ludogorets Razgrad.
At one stage, this was to be awarded to the highest-ranked champions (by UEFA coefficient) not to qualify for the group stage automatically. However, UEFA changed this to make it a qualifying berth rather than coefficient-related which would have benefitted Shakhtar Donetsk in most seasons due to their own high club coefficient, but Ukraine's falling league coefficient.
3 & 4) Two places are reserved for the two countries with the highest coefficient score in current season. This season, fifth place in the Premier League and second in the Dutch Eredivisie would go direct to the Champions League group stage. Right now, that would be Tottenham Hotspur and PSV Eindhoven.
What happened to the places based on historical performance?
Originally, two places were to be reserved for the clubs with the highest five-year UEFA coefficient who failed to qualify for the Champions League.
Although a club would have to qualify for Europe to be eligible, it still meant that there could be leapfrogging. For instance, Manchester United could finish 8th in the Premier League, win the FA Cup and be promoted into the Champions League based upon their five-year coefficient. Man United would therefore jump above the team that finished in fifth to play in the UCL.
It was decided that these two places are not "fully in line with the values and solidarity-based European sports model" with qualifying based on sporting merit.
Who will benefit from the two coefficient places?
The Netherlands getting an additional place in the Champions League piqued the interest, as it was a berth going to a team not from the "Big Five" leagues. However, historically this is an outlier.
If we look back at the previous five seasons, England and Spain take nine of the 10 slots.
2020-21: England, Spain
2019-20: Spain, Germany
2018-19: England, Spain
2017-18: England, Spain
2016-17: Spain, England
The Dutch Eredivisie has benefitted this season as it had three clubs in the group stage of the Europa Conference League (UECL), all of whom advanced. Feyenoord Rotterdam have reached the final, which has been just enough to get the Dutch second place in the coefficient table. But positions 1 and 3-6 are taken by the Big Five, showing that it takes a huge effort to claim a top two place.
In the five seasons before the UECL, the Dutch had finished 5th, 8th, 7th, 29th and 9th in the coefficient table.
If a country gets a coefficient place, that's an additional team in Europe. So, for instance, the Premier League would get eight places, with non-UCL positions dropping down one.
Champions League: 1-5
Europa League: 6, FA Cup winners
Europa Conference League: Carabao Cup winners
If the cup winners finish in the top 6, the places could drop to 7th and 8th in the table.
It also means it becomes technically possible for 11 clubs to qualify, over half the Premier League; the seven teams who qualify by domestic performance, the coefficient place and the three European titleholders (if they don't qualify via a domestic route).
Is the one-year coefficient system better than historical performance?
There are pros and cons.
On one side, the original plan rewarded teams that had played well in Europe over a five-year period. It created a safety net, and one that may well have given a big club such as Manchester United a route into the Champions League.
Over the past few seasons, Benfica (twice), Arsenal, AS Roma, Chelsea, FC Porto, Napoli and Shakhtar Donetsk would have gained a place under the original plan. Arsenal, Chelsea and Napoli would have benefitted under both systems.
Others argue that the new plan allows smaller clubs to benefit from the performances of others. Why should Getafe, Leicester and Real Sociedad get a UCL place for finishing fifth just because the other teams in their league have performed well in Europe in one particular season?
How will they decide the fixtures?
UEFA is expected to create four pots of nine teams, almost certainly based upon the five-year club coefficient. Each team will play two teams from each pot (one home, one away) to create an eight-match fixture list of roughly equal strength.
More "big matches" are created by the teams in the top pots being drawn against each other, which wasn't possible under the current system.
For instance, the teams in Pot 1 would draw two other clubs from Pot 1, 2, 3 and 4. Teams from the same association still cannot play each other in the group stage.
This is how the seeding pots would look, based on a 36-team Champions League intake using the new system and last season's final league tables.
Pot 1: Chelsea, Villarreal, Atletico Madrid, Manchester City, Inter Milan, Bayern Munich, Lille, Sporting CP, Real Madrid
Pot 2: Barcelona, Juventus, Manchester United, Paris Saint-Germain, Liverpool, Sevilla, Borussia Dortmund, FC Porto, Ajax
Pot 3: Shakhtar Donetsk, Lyon, RB Leipzig, FC Salzburg, Benfica, Atalanta, Zenit St Petersburg, Besiktas, Dynamo Kyiv
Pot 4: Dinamo Zagreb, Club Brugge, Young Boys, Leicester City, AC Milan, Real Sociedad, Malmo, VfL Wolfsburg, Sheriff Tiraspol
So, Premier League champions Manchester City could have a "Swiss Model" fixture list of: Atletico Madrid, Bayern Munich, Juventus, Paris Saint-Germain, Benfica, FC Salzburg, Young Boys, Sheriff Tiraspol.
So who goes through to the knockout rounds?
The top eight go directly through to the round of 16 and will be seeded in the draw. Clubs placed 9th to 24th will go into two-legged playoffs, with the winners going through as unseeded teams and the losers going out. There will be no dropdown of teams into the Europa League knockout rounds as of 2024-25. Clubs ranked 25th to 36th will be eliminated from Europe immediately.
It means the team ranked 24th in the group stage, only good enough for an unseeded place in Europa League under the current system, could actually go on to be European champions.
The competition then returns to the traditional format from the round of 16 onwards.
What about the Europa League and the Europa Conference League?
Both competitions will also switch to the Swiss Model from 2024, and will increase in size from 32 teams to 36.
There will be eight group-stage games in the Europa League, but only six in the Europa Conference League.
There will again be playoffs to reach the round of 16, but no drop down for the losers from the Europa League into the Europa Conference League either.
This is good news for the teams that took place in the group stage. One of the four Europa League semifinalists this season dropped down from the Champions League, and two of the Europa Conference League final four were in the Europa League group stage.