https://www.fide.com/fide-council-appro ... world-cup/
The major change
Using a Swiss as a qualifier for a knock out phase has been tried before, but hasn't always given satisfactory results. In the final Swiss round you may find two players with every incentive to take an early draw so that both qualify.A new two-stage format
Beginning in 2027, both World Cups will be played over 19 days and will consist of two distinct stages.
Stage 1: Swiss qualification
The opening stage will consist of Swiss-system tournaments played with a Fast Classical time control of 45 minutes plus a 30-second increment per move.
The Open World Cup will feature four Swiss pools, while the Women’s World Cup will be divided into two Swiss pools. Each Swiss tournament will be played over nine rounds across five days, with the pools balanced to ensure comparable playing strength.
The leading players from each pool will advance to the knockout stage:
Open World Cup: Top four players from each of the four pools (16 players total)
Women’s World Cup: Top eight players from each of the two pools (16 players total)
Stage 2: Knockout finals
The second stage will retain the traditional knockout.
"Fast Classical" is 75 minutes to move 60. Traditional British evening leagues used to play half that move count in a two and a half hour slot followed by an adjudication, adjournment or non-incremental quick play finish.