UEFA say the introduction of quarter-finals and promotion play-offs in a revised Nations League will make it a “more compelling” competition.
The new expanded format will debut in September 2024.
There will still be groups of four but, for the top 16 League A teams, the top two will advance to a quarter-final round trip in March 2025, with the group winners playing the runners-up.
The winners of these matches will enter the “Final Four” in June 2025.
As with the current format, the team finishing fourth in their League A group will be relegated.
But a team finishing third will enter a promotion play-off with a team finishing second in League B, and also held over two legs.
Scotland were promoted to League A for the 2024-25 event, with England being relegated to League B alongside Wales and Northern Ireland in League C.
“It makes the Nations League a more compelling competition, with more interesting and engaging knockout matches,” said UEFA assistant general secretary Giorgio Marchetti.
The revised format will lead to changes in the qualification system for the 2026 World Cup and Euro 2028.
Instead of the current 10 qualifying groups, there will be 12, six with five teams and six with four.
Countries that reach the “Final Four” will be placed in a group of four teams as their qualifying program cannot begin until September 2025.
The actual qualification process will start in March 2025, but only with groups of five teams and only with countries that are not yet involved in the Nations League.
UEFA said the changes will have no impact on the current international calendar and will accommodate any changes world governing body Fifa makes to it.
However, this only applies if Fifa meets the number of dates currently available for European football’s governing body.
The Nations League was launched in 2018 and has so far been won by Portugal and France.