This year’s women’s metric mile at the Prefontaine Classic could see the most sub-4 times in the meet’s history, thanks to the strongest field ever assembled in the United States.

Nearly half of the entrants in the 15-woman field have lifetime bests under that magic barrier. When these 7 toe the line, it will be the most ever in one race in the U.S. Their challenge will be to surpass the current record for most sub-4s of 5 set in the 2014 Pre Classic.

The race will feature a titanic clash of America’s best, along with world-class rivalries from distance powerhouses Kenya, Ethiopia, and Great Britain. The field includes 12 runners who were finalists in at least one event in Rio. Let’s start with one of the great American rivalries: Jenny Simpson vs. Shannon Rowbury.

Jenny Simpson earned America’s first Olympic medal in this event in Rio with a bronze, half a second ahead of 4th-placer Shannon Rowbury, who added to her stature as the only American with more than one Olympic final.  It was the latest chapter in one of the best rivalries seen in this event. Simpson owns a career 18-9 edge in their 1500/mile head-to-head meetings, dating back to their first, in the ’09 Pre Classic.

Simpson’s bronze in Rio was her first of the Olympic variety, but the 30-year has a pair even higher – a World Championships silver in 2013 and the gold from 2011, when she became the only American besides Mary Slaney in 1983 to earn a top-podium spot in a global event.  Simpson and Slaney each have eight career sub-4s, tied for the most by an American. Will there be a new leader after this year’s Pre race?

Rowbury, 32, has by far the best Olympic record by an American.  Her 7th-place finish in Beijing in 2008 was the best-ever by an American until she improved to 6th in London.  A frantic finish in Rio saw her best yet, an agonizing 4th behind rival Simpson.

She is the fastest American in history, running 3:56.29 in 2015 to shatter Slaney’s AR of 3:57.12 set in 1983 (less than two months before Rowbury was born).  Rowbury also has the American record in another Olympic event, chopping almost four seconds off Molly Huddle’s standard with a 14:38.92 in the 5000 last summer.  She has been the top-ranked American at 1500 by Track & Field News six times since 2008, including the last two.

Rowbury’s loss to Simpson in the 2009 Pre Classic 1500 was followed that summer with a national title and World Championships bronze, the first by an American in this event since Regina Jacobs in 1999.  Rowbury has five sub-4 performances, tied with Suzy Hamilton for the most by an American behind Slaney and Simpson.

Interestingly enough, even though the Simpson/Rowbury head-to-heads have produced no fewer than 11 sub-4 performances and 5 occasions where both have broken 4 in the same race, there has never been—yet—a Pre Classic with both breaking the barrier.

The two fastest Kenyans in history both earned Olympic medals in Rio last year and return to the Pre Classic having won different events with personal-best performances.

Faith Kipyegon, 23, earned Rio gold with a stunning finish in the 1500 that saw her cover the last two laps in 1:57.2, giving world record holder Genzebe Dibaba her first loss in almost two years. [More on Dibaba at Pre coming soon!]  Kipyegon ran her fastest 1500 – 3:56.41 – to capture last year’s Pre Classic with the fastest time ever recorded on U.S. soil.

This will be Kipyegon’s fifth appearance in the Pre Classic, where her slowest time (4:01.08) came as runner-up in 2013 as a 19-year-old.  Three weeks earlier she had destroyed the world Junior record at 3:56.98, then the fastest by a Kenyan of any age at the time.  She now has four career sub-3:57 times, the four fastest ever recorded by a Kenyan.

Kipyegon’s impressive career includes a silver from the 2015 World Championships and gold medals from the 2011 World Youth and 2012 World Junior titles in meet-record fashion.  She also owns World Junior cross-country titles in 2011 and 2013 and finished 6th in this year’s senior harrier race.

Hellen Obiri, 27, was formerly the Pre Classic and Kenyan record holder.  Instead of running the 1500 again last year, she moved up to the 5000 and lowered her PR by just under a minute to lead four Kenyans that included eventual Olympic gold medalist Vivian Cheruiyot.  In Rio Obiri lowered her PR again and finished with the silver.

Obiri has never lost at Hayward Field, twice recording the best times ever on U.S. soil in 1500 (3:58.58 in 2013, 3:57.05 in 2014) in addition to last year’s 5k PR (14:32.02).   Obiri owns a 10-3 career record over Kipyegon in the 1500.

Laura Muir, who will turn 24 on May 9, is the reigning IAAF Diamond League winner and the fastest from Great Britain since Kelly Holmes, who won the 2004 Olympics.  Her best of 3:55.22 last year is the fastest by anyone besides Dibaba since 1997.  This will be Muir’s only U.S. appearance besides last year’s 5th Avenue Mile, a narrow loss to Simpson who produced her record fifth such win.

Britain’s Laura Weightman, 25, earned the bronze medal in the 2014 European Championships after earlier taking silver to Kipyegon in the Commonwealth Games that summer.

Three Ethiopians include a pair of 20-year-olds who are no strangers to Oregon fans.  Dawit Seyaum and Gudaf Tsegay were gold and silver medalists, respectively, at the 2014 World Junior Championships held at Hayward Field.  Last year they led a 2-3-4 Ethiopian finish at the World Indoor Championships in Portland, with 22-year-old Axumawit Embaye taking 4th.  Embaye was the silver medalist in 2014.

Seyaum was runner-up in last year’s Pre Classic with a then-PR 3:58.10 and is Ethiopia’s third-fastest ever at 3:58.09.  She has been the No. 2-ranked Ethiopian the last three years by T&FN.  Tsegay ran her PR 4:00.18 for 3rd in last year’s Pre Classic.

Sifan Hassan, 24, is the second fastest in the field at 3:56.05 and won gold at last year’s World Indoor Championships in Portland.  Born in Ethiopia, she began competing for the Netherlands in 2014, world ranking in the top 5 the last three years by T&FN, topped by a No. 2 in 2014.  Hassan was 5th in 2014’s fantastic Pre Classic, when five ran sub-4, and was the Diamond League winner in 2015.

Americans Kate Grace, 28, and Shelby Houlihan, 24, were both finalists in their first Olympics last year.  Grace, a six-time Ivy League champ while at Yale, was 8th in the 800 and this winter lowered her 1500 best to 4:04.86.  Her 800 PR is 1:58.28.  Houlihan is a former NCAA 1500 champ from Arizona State and set her 1500 PR 4:03.39 in last year’s Pre Classic.  She concentrated on the 5k in the summer, taking 11th in Rio.  In early March of this year, Houlihan won her first U.S. titles, doubling in the mile and 2-mile indoors.

Rababe Arafi, 26, of Morocco finished just outside of the medals in the 2015 Beijing World Championships, taking 4th in the 800.  She also was a finalist in the 1500, as she was in Rio last summer.

Poland’s Sofia Ennaoui, 21, was a finalist in Rio last summer and earned bronze in March at the European Indoor Championships.  She was 5th in the 2014 World Junior Championships held at Hayward Field.

Australia’s Linden Hall, 25, ran her lifetime best of 4:01.78  in finishing 5th at last year’s Pre Classic.  No Aussie has ever broken 4-minutes. Could she be the first?

Women’s 1500 Meters Personal Best
Laura Muir (Great Britain) 3:55.22
Sifan Hassan (Netherlands) 3:56.05
Shannon Rowbury (USA) 3:56.29
Faith Kipyegon (Kenya) 3:56.41
Hellen Obiri (Kenya) 3:57.05
Jenny Simpson (USA) 3:57.22
Dawit Seyaum (Ethiopia) 3:58.09
Laura Weightman (Great Britain) 4:00.17
Gudaf Tsegay (Ethiopia) 4:00.18
Sofia Ennaoui (Poland) 4:01.00
Linden Hall (Australia) .4:01.78
Axumawit Embaye (Ethiopia) 4:02.35
Rababe Arafi (Morocco) 4:02.71
Shelby Houlihan (USA) 4:03.39
Kate Grace (USA) 4:04.86