2025 World Championships
- July 27 – August 3, 2025 (pool swimming)
- Singapore, Singapore
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- LCM (50m)
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By The Numbers – Men’s 400 Freestyle
- World Record: 3:39.96 – Lukas Märtens, Germany (2025)
- World Junior Record: 3:44.31 – Petar Mitsin, Bulgaria (2023)
- Championship Record: 3:40.07 – Paul Biedermann, Germany (2009)
- 2024 Olympic Champion: Lukas Märtens, Germany – 3 :41.78
- 2023 World Champion: Sam Short, Australia – 3:40.68
The World Record Holder
Coming off the Olympic year, no one really knew what to expect. It seemed like the 2025 season was going to be about reset—it kicked off the first typical Olympic cycle the sport has had since the build up to the 2016 Olympics. Many Olympians announced extended breaks after competing in Paris.
But any ideas that 2025 might be a “slow” year were disabused in MONTH when Lukas Märtens broke Paul Biedermann’s super-suited 400 freestyle world record. Märtens became the first man to break the 3:40 barrier, setting a blistering pace on the first half of his race and holding on to touch in 3:39.96.
The moment was the culmination of years of work for Märtens, who seriously broke onto the international scene in 2022. He was a constant presence in the World Championship final and on the podium. After he scared Biedermann’s world record at the 2024 European Championships, he ascended to the top of the international stage by winning Olympic gold in Paris.
Compared to the other events on the 2025 World Championship schedule, this event is stacked. Even so, Märtens remains the clear favorite heading into Singapore as he looks for his first long-course 400 freestyle world championship title.
The Paris Podium Reloads
Kim Woo-min (credit: Fabio Cetti)
The event’s depth will be on full display during the first night of competition. While some events at this meet are plagued with absences, seven of the eight Olympic finalists are slated to suit up in Singapore. The only one missing is the eighth-place finisher, American Aaron Shackell.
That means that all three Paris Olympic medalists—Märtens, Elijah Winnington, and Kim Woo-min—will be in the water. Paris was the second time the three shared an international podium as it was Kim, Winnington, and Märtens (in that order) receiving medals in Doha at the 2024 World Championships. Winnington is a world champion himself, earning the crown in 2022 with a 3:41.22, which is still his lifetime best and makes him the eighth-fastest performer in history.
Winnington ranks fifth in the world this season, sneaking under the 3:44 mark with a 3:43.99 at the 2025 Australian Trials in June. Kim has had a quieter buildup to the World Championships, and checks in with a season-best 3:45.54 from March that ranks tenth in the world. He swam a lifetime best 3:42.42 at the 2024 Mare Nostrum Swim Tour and was 3:42.50 in Paris.
More Paris Finalists Check In
Not only will the entire Paris Olympic podium be in the water, with Sam Short present and accounted for, this field also features the last three long-course world champions. Now 21, Short won the 2023 title by two-hundredths over Tokyo Olympic champion Ahmed Hafnaoui, swimming a 3:40.68 that now ranks him as the fifth-fastest performer all-time.
Short had a difficult lead-up to the Paris Olympics due to illness. He still finished fourth, though got out-touched by Kim by .14 seconds and finished just off the podium in 3:42.64. His lifetime best 3:40.68 would’ve earned gold in the race, as Märtens won gold in 3:41.78.
Samuel Short (photo: Jack Spitser)
Third through fifth was tight in the Paris final, with Brazil’s Guilherme Costa heartbroken in fifth with a 3:42.76, .26 seconds behind Kim. The swim was still a lifetime best for Costa, breaking the Americas record and moving him to 14th on the all-time performer list. Costa is often a main animator of the hunt for the podium down the final stretch of the race. He has a strong back-half that helped him win bronze at the 2022 World Championships and fourth in 2023 and 2024. Costa has put himself in position to be in the mix again with a 3:45.35 season-best that ranks ninth in the world and seventh among those racing this event in Singapore.
The other two Paris finalists in the field are Fei Liwei and Oliver Klemet. Fei finished sixth in Paris and with a 3:45.54 season-best, is sitting bunched with Kristof Rasovszky, Costa, Kim, and Luka Mijatovic in the global rankings. Meanwhile, Klemet has established himself as part of the strong German distance crew that includes Märtens, Sven Schwarz, and Florian Wellbrock.
Klemet owns a lifetime 3:42.81. He was well off that in Paris with a 3:46.59 for seventh, but approached the mark April with his season-best 3:43.40. That effort makes him one of just five swimmers to break 3:44 this season. However, Klemet will have already raced at the World Championships; he earned top 10 finishes in the men’s 5k and 10k open water events and helped Germany win the mixed 1500 relay. We’ve seen mixed results with swimmers transitioning from open water to the pool at the World Championships, so we’ll see how Klemet responds. In Paris, open water followed the pool swimming action.
New Kids On The Block
As the Olympic finalists look to shore up another appearance in the 400 freestyle international final, there are several fast rising names to watch that are hoping to get in on the action.
After the U.S. men had stagnated in this event for the better part of the last decade, they took a big step forward at the 2025 U.S. Nationals. Texas Longhorn Rex Maurer delivered, translating the gains he made in the yards pool during his first season training with Bob Bowman to a U.S. Open Record 3:43.33 that makes him the third-fastest American man in history.
Maurer ranks third in the world this season behind only Märtens and Short, a strong position to find himself in as he heads towards his first senior long-course World Championship appearance. He was not the only exciting part of that final in Indianapolis. The 16-year-old Mijatovic also qualified for his first senior World Championships, swimming 3:45.71 to break the 15-16 National Age Group Record. Mijatovic has been putting up sensational times in the 400/800/1500 freestyle for the past year and will now get a big opportunity to learn on the senior stage.
Rex Maurer (photo: Jack Spitser)
SwimSwam has confirmed that a significant portion of Team USA got food poisoning at the team’s training camp in Phuket, Thailand, with about ten athletes staying behind while the rest of the team traveled to Singapore. SwimSwam does not know whether Maurer or Mijatovic contracted the illness, but it will be something to watch, especially with this event so early in the meet.
Beyond the American men’s changing of the guard in this event, another young swimmer to keep an eye on is Ahmed Jaouadi. Jaouadi, 20, has already made himself known on the international stage, winning gold in the 1500 freestyle and bronze in the 800 freestyle at the 2024 Short Course World Championships.
Jaouadi made the Olympic final in both the 800 and 1500 freestyle in Paris, taking fourth in the former. The 400 freestyle is at the shorter end of his range; he just missed the Olympic final last simmer with a 9th place effort (3:46.19) and has a 3:45.95 lifetime best.
Bulgaria’s Petar Mitsin made headlines in 2023 when he broke Mack Horton’s world junior record at the 2023 European Junior Championships with a 3:44.31. Two years later, that time remains Mitsin’s best effort. He did not get close to it at the Olympics, swimming 3:49.30. He’s been better already this season with a 3:46.66 at the 2025 LEN U23 European Championships, but has not broken 3:46 since that swim two years ago.
Contenders For The Final
Let’s be clear, with seven of the eight Olympic finalists in the field, it’s going to be a challenge to make the final. But, there are plenty of swimmers aiming to dethrone the Paris eight, and all it takes is a strong morning swim from an “outside” contender to knock a big name out.
Plenty will be trying, including the reigning 10km Olympic champion, Kristof Rasovszky. While he’s best known for his open water exploits—and has already won bronze in the 1500 relay in Singapore—he had a breakthrough in the 400 freestyle this spring. Rasovszky dropped over a second from his lifetime best in April, going from 3:46.56 to 3:45.32 and lowering the Hungarian national record.
With Wellbrock not competing in this event at Worlds, there’s a big gap in the season rankings between 5th ranked Winnington (3:43.99) and 7th ranked Rasovszky (3:45.32) but provided Rasovszky manages the transition from open water to the pool well he’ll be one of the main non-Olympic final swimmers hunting for a finals lane.
Kristof Rasovszky (credit: Fabio Cetti)
Other candidates likely to push the pace include Lucas Henveaux, Zhang Zhanshou, and Marco De Tullio. Henveaux returned to the NCAA and the Cal Golden Bears for the second part of the college season. He made a big impact for the Bears and saw big drops in his yards times. The Belgian has been steadily improving over the past few years in the long-course pool as well. His lifetime best is a 3:44.61 from his 5th place finish at the 2024 World Championships and he has a season-best of 3:46.76.
De Tullio owns a lifetime best of 3:44.14 from the 2022 World Championships. After a disappointing 2024 season, he cleared the 3:45 barrier for the first time in two years at Sette Colli, swimming a 3:44.89 for the sixth-fastest swim of his career.
Meanwhile, Zhang Zhanshou is still trying to clear that mark for the first time in his career. He owns a lifetime best 3:45.11 from the 2023 Chinese Championships. Zhang finished 12th in this event at the Paris Olympics, tied with Henveaux at 3:46.76. It took a 3:45.75 to make the Olympic final, though it looks like that time may drop slightly in Singapore.
Zalan Sarkany had an excellent NCAA season and is another name to track, as are France’s David Aubry, and Sweden’s Victor Johansson, and Switzerland’s Antonio Djakovic, who all made a World Championship final during the last Olympic quad.
SwimSwam Picks
| Place | Swimmer | Nation | Season Best | Lifetime Best |
| 1 | Lukas Märtens | Germany | 3:39.96 | 3:39.96 |
| 2 | Sam Short | Australia | 3:41.09 | 3:40.68 |
| 3 | Elijah Winnington | Australia | 3:43.99 | 3:41.22 |
| 4 | Kim Woo-min | South Korea | 3:45.54 | 3:42.42 |
| 5 | Guilherme Costa | Brazil | 3:45.35 | 3:42.76 |
| 6 | Rex Maurer | United States | 3:43.33 | 3:43.33 |
| 7 | Oliver Klemet | Germany | 3:43.40 | 3:43.40 |
| 8 | Fei Liwei | China | 3:45.57 | 3:44.24 |
Dark Horse: Daniel Wiffen (Ireland) – 800 freestyle Olympic champion Daniel Wiffen is the dark horse in this race purely because we don’t know if he’ll swim it. He’s entered, as he typically is, but we’ve often seen him scratch this race to prioritize the 800 and 1500 freestyle later in the meet. He did swim it at the 2024 World Championships, taking 7th in 3:46.65. Wiffen’s lifetime best of 3:44.35 would make him an interesting candidate for the final. If he swims, expect him to be in the hunt, but it’s more likely he skips the fight to prepare for the battle the men’s distance events have become.
Won’t be an American on the podium here (as is usual with this event) but the future is so bright for us in this event, exciting to see what has transpired recently. That being said I wouldn’t be baffled if Martens lost to Short.
Rex for the silver
I know Martens has the WR but something tells me Short – won’t be a massive surprise – should be close.
I’d take Sam Short based on performance in big races. His trials time suggests that a 3:39 could be in the cards and Martens has yet to swim a seasons best in a championship final
My money is on the reigning olympic champion. Big final, big win for Lukas.
Is it too much to say I think Rex is gonna smash the American record and go 3:41?
with you on that. Dnn’t think 3:43.3 is anywhere near his ceiling for this season
Where is Kieran smith?
Sitting at home, he did not qualify
Think David Aubry is gonna take it lowkey
While the women’s 800 free is the most anticipated event I think this is the big one on the men’s side.
Going to a great race, funny to say that after Martens breaks Supersuit WR this year, but so many great swimmers Short, Winnington, Woo-Min & Costa.
I’d say 100 free is the marquee match-up this year. But 400 should be great, along with the usual distance races.