The flattest, fastest and prettiest road race in San Diego County is officially over the hill.

The Carlsbad 5000 will turn 40 years old on Sunday, though it’s never looked better or been healthier. More than 20,000 people — 8,500 runners and 11,500 fans — are expected to pack the coastal community yet again for a picturesque celebration of foot speed.

Here’s a look at the Carlsbad 5000’s past, present and future as the race arrives:

What it is: Dubbed “The World’s Fastest 5K,” the Carlsbad 5000 is a 3.1-mile race down Coast Highway 101. The starting line is located at Grand Avenue and Carlsbad Boulevard, with runners finishing under the Carlsbad sign at Carlsbad Village Drive and Carlsbad Boulevard.

Schedule: The Carlsbad 5000 features nine different age and skill-level categories, with the first race starting at 7 a.m. and the last one ending around 1 p.m. The fastest times will be posted by the Elite Men, who race at 12:30 p.m., followed by the Elite Women at 12:35 p.m.

What’s at stake: The Carlsbad 5000 splits a $25,000 prize purse across the Open and Masters divisions. Any runner who breaks the American record receives an extra $5,000. Winners also receive handmade surfboard trophies.

The first time: The first Carlsbad 5000 was held in 1986, with American Olympians Steve Scott (13 minutes, 32 seconds) and PattiSue Plumer (15:31) the top men’s and women’s finishers. Just 41 men and 35 women have posted better times in the 39 years since then, an impressive feat given the advances in equipment and training over the past four decades.

The last time: Two-time Olympian Sam Atkin of England won last year’s men’s elite race, posting a time of 13:24 and beating American Brian Barraza by eight seconds. Ethiopia’s Lemlem Hailu won the women’s elite event in 15:13, beating Mexico’s Laura Galvan by 17 seconds and denying Galvan her third consecutive Carlsbad 5000 win. Atkin and Hailu each won $5,000.

But why? Some of Sunday’s racers will attempt what Carlsbad 5000 officials call the All Day 20K, competing in the day’s first four 5K races for a total distance of 20K (or 12.4 miles). Those who register for the All Day 20K get access to recovery equipment, food and drink and their own bathrooms as well as a free gift from Lululemon. How popular is the early-morning gauntlet? This year’s slots are all full.

We know them: Olympians Meb Keflezighi and Deena Castor will serve as ambassadors for this year’s race. Keflezighi starred at San Diego High School and UCLA, and has run the Carlsbad 5000 twice. Kastor set the women’s 5K world record at the 2002 Carlsbad 5000; the Aguora Hills native has also held American records in the marathon and half-marathon.

Too late to train? Runners can already sign up for the 2027 Carlsbad 5000, which will be held next April 5. Registration for next year is $20 for the Junior Carlsbad race, $35 for any of the 5Ks and $90 for the All Day 20K.

Carlsbad 5000

When: Sunday

Where: Starting line at Grand Avenue and Carlsbad Boulevard; finish line at Carlsbad Village Drive and Carlsbad Boulevard

Schedule: Women’s Masters at 7 a.m.; Men’s Masters at 7:50 a.m.; Women’s Open at 8:40 a.m.; Men’s Open at 9:30 a.m.; People’s Race at 10:30 a.m; Kids 1-mile at 11:45 a.m.; Kids 1/2-mile at noon; Men’s Elite at 12:30 p.m.; Women’s Elite at 12:35 p.m.