The 2026 London Marathon is upon us, and if you thought running 26.2 miles was hard enough, try doing it in a full-body inflatable T-rex costume. Arnie Delstanche is back to improve his own Guinness World Record of 4:07:46 for fastest marathon in such attire, because apparently once wasn't enough.

The elite fields are as stacked as a runner's carb-loading dinner. On the men's side, defending champion Sabastian Sawe of Kenya, who won in 2:02:27 last year, faces tough competition from Uganda's half marathon world record-holder Jacob Kiplimo and Ethiopia's Deresa Geleta, the 20th fastest marathoner ever with a 2:03:27 at the 2024 Seville Marathon. Sawe, ever the modest sort, told BBC Sport: "Not much pressure on me because I run my own race, and it is only the best moment to be here." He also believes a new world record is "only a matter of time." We'll see.

In the women's elite race, Ethiopia's Tigst Assefa returns as defending champion after her women-only world record of 2:15:50 last year. She hasn't been shy about wanting to break her own record. Kenya's Joyciline Jepkosgei, last year's runner-up, aims to do one better, while newcomer Hellen Obiri makes her London debut after racing in New York and Boston - where, crucially, they don't use pacers. The trio went through 10km in 31 minutes, faster than expected, suggesting a tactical game of tiring out the newcomer.

The wheelchair races are equally fierce. Switzerland's Marcel Hug, the greatest wheelchair marathoner in history with 42 Abbott World Marathon Majors wins, is 15 minutes away from winning his eighth London Marathon, which would tie him with David Weir for most wins in London. He and Leo Xingchuan have broken away early. In the women's wheelchair race, heavy favourite Catherine Debrunner and Tatyana McFadden are rotating the lead, each making it "slightly more difficult" for the other. Debrunner, who won five gold medals at the 2024 Paris Paralympics, is aiming for both the title and the world record she missed by two seconds in 2025.

A slight hiccup: Great Britain's Eden Rainbow-Cooper had a puncture before the wheelchair race started but was allowed to switch to a spare. She then apparently didn't start after all, leaving her podium hopes in doubt.

Beyond the elites, 76 people will attempt 73 different Guinness World Records. Mark Goulder will try to run the fastest marathon blindfolded and tethered, targeting 3:20:00, guided by his friend Alex, inspired by his brother Bobby's Stargardt's disease. Simon Fannon, meanwhile, will try to run as slowly as possible while knitting the longest scarf (minimum 3.7m) in six hours, raising funds for the Huntington's Disease Association after his mother's diagnosis.

The official starters are Britain's four-time Olympic gold medallist Mo Farah, returning for the first time since retiring in 2024, and Rugby World Cup-winning star Ellie Kildunne. They'll send off more than 59,000 participants from Blackheath to the Mall.

The marathon's popularity has exploded: more than 1.1 million people entered the ballot this year - 750,000 more than four years ago. A third were aged 18-29, with female entrants making up the biggest percentage of those under 30. Running clubs or 'crews' focused on inclusivity and coffee rather than super-fast times are fuelling the boom, particularly among Gen Z women seeking real-life experiences post-pandemic.

The official charity is Marie Curie, the UK's leading end-of-life charity, aiming to raise £2m for terminal illness awareness and funds.

So as the capital enjoys incredible weather, the 2026 London Marathon is off and running. We'll keep you updated on who wins, who sets records, and whether Arnie Delstanche's T-rex costume survives the full 26.2 miles.