Follow our live updates from the 2023 Boston Marathon.

Hellen Obiri has done just about everything in running.

Obiri, a 33-year-old Kenyan, has gone to three Olympics and won a medal in two of them. She is the only woman to have won world titles in indoor track, outdoor track and cross-country. She has won six of her eight half-marathons and finished on the podium in the others.

There are just a few items left on her checklist.

She would like to win Olympic gold and set a world record. Doing either in the marathon seems like a legitimate possibility, even if she has run the distance in elite competition only once.

“I think for the second one, I’ll know what I’m doing,” Obiri said before announcing she would be running in Monday’s Boston Marathon, joining the fastest and most decorated lineup the race has had.

That calm confidence is sure to stoke fear in her competitors, despite the depth of the field. Of the women who will toe the starting line in suburban Hopkinton, Mass., 14 have run the marathon faster than 2 hours 21 minutes. Five have run under 2:18.

That’s exactly why her coach, Dathan Ritzenhein, thought the race would be good for Obiri.

“She’s just a good racer,” Ritzenhein said. “She’s best at competing.”

She is doing so under a new coach and a new team: In 2022, she enlisted Ritzenhein, joined the On Athletics Club and moved to Boulder, Colo., to train with the group a few weeks before her marathon debut in New York City in November.

It was a notable transition. Obiri is from Kisii, a mountainous area in southwestern Kenya, and spent most of her time training in and around Nairobi, the nation’s capital. It’s common for many top American runners to spend time training in Kenya. The reverse is less so.

Expectations for her marathon debut were high. A mural of Obiri was painted on a multistory building in Brooklyn when she arrived in New York. “Don’t know Hellen Obiri? You will,” the On Running ad read.

If she was feeling outside pressure, she didn’t show it. At a dinner in the days before the marathon, she nonchalantly asked amateur runners about the course and the crowds. When answers included the word “fun,” Ritzenhein chimed in. Raising his eyebrows, he told Obiri it might not be all fun.

With her collection of accolades, Obiri knows a thing or two about moving through the pain cave. “If you tell your mind, ‘I’m tired,’ you’ll give up,” she said. So she instead repeats, “I’m strong, I’m strong.”

But she was underfueled in New York, she said, and she began shutting down in the last few miles. She finished sixth in 2:25:49, two minutes behind the winner, her countrywoman Sharon Lokedi.

Obiri moved back to Kenya after the marathon as she and Ritzenhein worked to get her back to Boulder with her husband, Tom Nyaundi, and their 7-year-old daughter, Tania.

Obiri was ready for the change. For the past 12 years, her coaches, including the longtime coach Ricky Simms, have advised her from a distance. Turns out she needed someone to tell her to slow down, she said, laughing. She wasn’t going to be able to do it herself.

“When I went back to Kenya for four months after the marathon, Dathan was sending me a program, but he wasn’t there physically to say, ‘You can’t go crazy, control yourself,’” she said. “It’s important to have Dathan here telling me, ‘Don’t go crazy, you are doing this, go like this,’” she said, noting how he improves her form.

It was hard for her at first. A natural competitor, Obiri likes to go fast.

“I want to say, ‘Coach, this pace is so slow,’” she said, “and he says, ‘No, I know what I’m doing.’”

That has shown in her training logs and in her results. She won the New York City Half Marathon on March 19 with a course-record time of 1:07:21. (It’s a hard course; her best time in the distance is 1:04:22.) The next day, she moved to Boulder with her family.

She was quick to hop into training sessions with her teammates. On March 28, she joined Joe Klecker, one of her teammates, for a long run. For Klecker, a runner who focuses on the 5,000 and 10,000 meters, that meant doing 18 miles. Obiri did those 18 — plus another seven for good measure, all at a pace that hovered around 5:35 per mile, the equivalent of a marathon around 2:26.

“He went with Hellen and took the beating,” Ritzenhein said.

“Which is funny because it takes a lot to beat up Joe Klecker,” said Andrew Wheating, a two-time Olympian and the team’s operations and content manager.

Two days later, Obiri joined Klecker and the rest of the team for a workout. Ritzenhein figured that Hellen “has got to be tired.”

“You would think,” Wheating said.

Obiri was essentially doing a 50-minute fartlek run — a ladder of fast intervals with equal “rest,” which simply means running but not as quickly — alongside Alicia Monson. Ritzenhein was excited for Monson, the freshly minted American record-holder in the women’s 10,000. It has gotten more challenging to find women who can keep up with Monson.

Before the start of the run, Ritzenhein advised Obiri to take it easy.

“You just ran 25 miles,” he told her. “You have to go easy. Otherwise I’ll yell! I’m a big yeller!”

(He is not a big yeller.)

During the run, Ritzenhein drove his pickup truck and stopped periodically to shout encouragement and hand Obiri water bottles. About a half-hour into the run, he pulled the truck to the side as Obiri and Monson came into view.

“If she’s still got that bottle, I’m going to be so impressed,” Ritzenhein said. “And it also better be gone.”

Obiri, without breaking stride, handed him the bottle. It was almost gone.

Regularly refueling was one of the hardest things for her to master, Obiri said a few days before flying to Boston. In Kenya, she would often do 20-mile runs without any water, gels or electrolytes at all. Now she’s become accustomed to a plan. “Four sips every five kilometers,” she said.

She is eager to learn, and she is relieved to be doing so with her family alongside her. They will help her a lot in terms of training and preparation, she and Ritzenhein echoed. Last year, with a nine-hour time difference between Colorado and Kenya, she was often missing her family’s presence and their phone calls, too. It took a toll.

Her family was also excited for the move. Tania, the proud owner of “Frozen” Crocs, was eager to see snow, even if she was quickly disenchanted with the cold. Soon to be 8, she was also excited to watch her mother win races in real life instead of on TV. Both Tania and Nyaundi will be in Boston to watch Obiri compete.

That’s always extra motivation, Obiri said. She hates the idea of them waiting too long for her.

But in Boston, with a notoriously difficult and often slow course, she is going to have to keep herself in check, she said. “It’s about patience in a marathon. I’ve got to focus on patience, patience, patience,” she said, speaking like a student of the distance and an expert in the art of racing. “That’s what I’m going to do in Boston.”

Does that mean a slow and steady race for Obiri?

Ritzenhein, who himself has placed in the top 10 of the race, seems to know his athlete and the course well. “I would say Boston can be fast,” he said.