A total of 16 golds are up for grabs on the sixth full day of competition in Paris, which is again bracing for extreme weather with storm warnings in place early Thursday morning.
US star Biles steps back into the spotlight seeking to become the first woman ever to regain the Olympic all-around title after she famously withdrew in Tokyo with the debilitating "Twisties".
The 27-year-old returned to the top of the podium on Tuesday with team gold, her eighth Olympic medal, five of them gold, to become the most decorated US Olympic gymnast.
Biles, the reigning world champion, wants to do it in style with a new skill on uneven bars that would be the sixth unique skill named after her.
But Biles faces a stern challenge from teammate Sunisa Lee, reigning Olympic all-around champion, who is on a comeback trail every bit as compelling as her compatriot.
Lee was diagnosed with two undisclosed kidney conditions in early 2023. However, she declared herself "in remission" in April and counts herself stronger than she was in Tokyo.
Another top contender is Brazil's Rebeca Andrade, who said it was an honour just to compete against Biles.
"She's a reference, a role model for the whole world, gymnastics and athletes alike to see how happy she is to compete. That's what's sport is all about," said Andrade.
'Red hot form'
Meanwhile, the athletics programme gets under way with the men's and women's 20km walk races.
Italy's Massimo Stano is bidding to become the first man to win back-to-back gold in the event after triumphing in Tokyo but world number one Perseus Karlstrom from Sweden and Japan's Koki Ikeda will provide stiff competition.
Compatriot Antonella Palmisano is also defending her Olympic title in Paris, where the race will be held with the Eiffel Tower as a backdrop.
Another packed schedule in the pool includes the women's 200m butterfly final, featuring 17-year-old Canadian prodigy Summer McIntosh, fast becoming one of the stars of the Games.
Already 400m medley champion and 400m freestyle runner-up, McIntosh faces a stacked field including defending champion Zhang Yufei from China.
The 200m women's breaststroke stars South Africa's Tatjana Smith, aiming to become the first woman to do the double since compatriot Penny Heyns at Atlanta 1996.
Smith won Tokyo 200m gold in a world record 2:18.95 and is in red-hot form after securing the 100m title on Monday.
Other golds up for grabs include kayak canoeing, fencing, judo, rowing, sailing, shooting.
Golf tees off with eight of the world's top 10 competing, including two-time major champion Collin Morikawa and the world's top-ranked player Scottie Scheffler.
The variable Paris weather that has veered from torrential rain at the opening ceremony to a heatwave just a few days later could be a factor again.
Paris and the surrounding areas have been placed on orange alert -- the second-highest level -- with heavy rain, hail, and winds of up to 90 kilometres per hour forecast.
Archery already fell victim to the storms, with the final session being postponed on Wednesday.
