BOSTON (AP) — Meb Keflezighi’s last Boston Marathon. Galen Rupp’s first. Two defending champions on the women’s side (sort of), and Lemi Berhanu Hayle returns to go for his second straight men’s title.

The 121st edition of the Boston Marathon left Hopkinton on Monday morning for the 26.2-mile trek to Copley Square, with more than 30,000 runners expected to line up under partly cloudy skies and temperatures in the mid-60s — a little warmer than the competitors would like. But a tailwind gusting up to 30 mph could mean fast times, at least among the elite runners who would finish before the hottest part of the day.

The race has largely returned to normal four years after two bombs at the finish line in 2013 killed three people and wounded hundreds more. A new documentary that premiered in Boston on Saturday night, narrated by Matt Damon, tells that story along with many others from the history of the world’s longest running long run.

This year, some of the best will be back in the pack, including a formerly homeless man who is running to raise money for a homeless shelter , and Ben Beach going for an unprecedented 50th straight Boston finish.

Here are some other things to look for in Monday’s race:

MEB’S FAREWELL

Keflezighi, whose emotional victory the year after the finish line bombings was the first for an American man in three decades, says he is running Boston for the last time.

“People say, ‘Why stop? You’re still at a high level.’ But it takes a lot out of you,” he said as he prepared to embark on his victory lap . “I had the best job in the world for a long, long time.”

A four-time Olympian who earned a silver medal in Athens in 2004 and won the 2009 New York City Marathon — both times also ending long American droughts — Keflezighi’s 2014 win in Boston is one of the signature moments in the race’s century-old history. With the names of the bombing victims written on his bib and chants of “U-S-A!” coming from the crowd, he claimed the first American title since 1985.

But he will turn 42 in May. He plans one more run in New York before retiring from competitive racing.

WOMEN TIMES TWO

Atsede Baysa is back to defend her women’s title, but she will be joined in the field by another returning winner fresh off a Boston victory.

Buzunesh Deba was anointed the 2014 Boston champion in December — more than two years after the race — when Rita Jeptoo was stripped of the title for testing positive for performance-enhancing drugs. Jeptoo, whose 2006 and 2013 victories remain unchallenged, is the first person to break the tape on Boylston Street and be disqualified since Rosie Ruiz famously took a shortcut to the finish line in 1980.

Deba is hoping for another victory and a first chance at all the honors that come with it.

HAIL HAYLE

Hayle gave Ethiopia its first-ever sweep last year when he pulled away from countryman and two-time champion (2013, 2015) Lelisa Desisa with about a mile to go to join Baysa on the victory stand.

In all, Ethiopia claimed the top three spots on the men’s side (pushing the once-dominant Kenyans down to the next four spots), and the top two women. It was the fourth straight year an Ethiopian has won (including Deba, who never actually made it to the top of the podium).

Joining Hayle in the field this year are fellow Ethiopians Yemane Tsegay and Dino Sefir.

AMERICAN HOPES

Rupp, the bronze medalist in the Rio Olympics, will be running Boston for the first time.

Already a silver medalist and U.S. record-holder in the 10,000 meters, he ran the fastest marathon time ever for an American in the Summer Games: 2 hours, 10 minutes, 5 seconds.

“I’m at a point in my career where I feel like I can compete with anybody,” he said this week. “And there’s no place better to do it than Boston.”

With two-time fourth-place finisher Shalane Flanagan out with a back injury, the U.S. hopes on the women’s side are represented by Desi Linden, a two-time Olympian who has thrice placed in the top 10 in Boston.

WARM AND FUZZY

The honors won’t end for the winners on Monday: A guide dog training center in New York will name two puppies from a litter expected during the race after the men’s and women’s champions. Guiding Eyes for the Blind CEO Thomas Panek, who will be running Boston, visited the finish line with two other puppies on Sunday — these were a few weeks old already — and attracted a lot of attention .

If they pass their training, the puppies will be sent to people who are blind or visually impaired, or as service dogs for children with autism. Spokeswoman Julia Hadlock said Guiding Eyes is the only center in the country that trains dogs for running, along with their other functions.

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AP Sports Writer Kyle Hightower and Associated Press Writer William J. Kole contributed to this story.