IOC President Kirsty Coventry said the decision is intended to ensure fairness in competition. “As a former athlete, I passionately believe in the rights of all Olympians to take part in fair competition,” she stated. “It is absolutely clear that it would not be fair for biological males to compete in the female category. In addition, in some sports it would simply not be safe.”

The IOC said the policy is based on research indicating that male sex development provides advantages in strength, power, and endurance, which may persist after transition. The policy document states that males experience three testosterone peaks—in utero, during infancy, and from puberty through adulthood—which contribute to “individual sex-based performance advantages.”

The decision follows years of debate involving high-profile athletes. Algerian boxer Imane Khelif, who won gold at the Paris 2024 Games after having faced online abuse and accusations regarding her gender eligibility. Khelif faced further scrutiny after a leaked medical report allegedly indicated an XY chromosome pattern and internal testicles. The report suggested she may have 5-alpha reductase deficiency, a condition in which genetic males may be raised as females due to ambiguous external genitalia. Her father, Omar Khelif, said, “My child is a girl. She was raised as a girl.” Under the new policy, such athletes would be excluded from female competition unless they can demonstrate the absence of performance-enhancing effects from testosterone.

South African runner Caster Semenya has also been central to the debate. She recently ended a seven-year legal challenge against regulations that required her to lower her natural testosterone levels. The new IOC policy replaces hormone monitoring with a permanent genetic screening approach.

The policy received political support from U.S. President Donald Trump, who wrote on Truth Social: “Congratulations to the International Olympic Committee on their decision to ban Men from Women’s Sports. This is only happening because of my powerful Executive Order, standing up for Women and Girls!”

Legal challenges are expected, with experts anticipating cases at the Court of Arbitration for Sport in Lausanne ahead of the LA28 Games.

The IOC said the policy will not apply retroactively and will not affect grassroots or recreational sports . For elite athletes, the SRY screening will be conducted through saliva, cheek swab, or blood tests and is described as “unintrusive.”

Coventry said athlete welfare will be considered in the process. “Every athlete must be treated with dignity and respect, and athletes will need to be screened only once in their lifetime,” she said, adding that education, counselling, and mental health support will be provided. Athletes who test SRY-positive will be eligible to compete in male, mixed, or “open” categories where available.

The policy includes an exception for individuals with Complete Androgen Insensitivity Syndrome (CAIS). Athletes with CAIS may be eligible for the female category despite testing SRY-positive if they do not benefit from the performance effects of testosterone. This requires a clinical diagnosis confirming that their bodies do not respond to male sex hormones.

The IOC said that in most cases, the presence of the SRY gene is “highly accurate evidence” of male sex development and associated performance advantages, while noting that the CAIS exception applies where these biological factors do not translate into a competitive advantage.

"It really does feel as though the state wants to kill us," said Helen Belcher, a prominent trans rights campaigner and chair of the advocacy group TransActual.

Speaking to the AFP following the court’s decision, Belcher said the ruling represents a fundamental denial of trans people's identities and lived realities.

Belcher, 61, who is also a Liberal Democrat politician, said the implications of the ruling are already being felt within the trans community.

"I fear for people's mental health. I fear for people's physical health. I fear for people's ability to earn money. They've issued a ruling that sex is biological, but they haven't defined what biological means,” said Belcher

Belcher warned and reasoned that the judgment leans on a rigid and outdated framework, dismissing scientific literature that recognises sex and gender as complex spectrums.

“They're relying very much on a Trumpian, evangelical Christian simplistic world model,” Belcher said, “ignoring all huge amounts of scientific literature, which says that sex is not binary, it's not simple, it's really complex. In their judgment, they have decided basically that intersex people and non-binary people don't exist. And it's awful."

Belcher, who transitioned more than 20 years ago, described the ruling as a deeply personal blow.

“To go through that process - sometimes painful process - of getting to understand myself, having invasive medical questioning, some painful surgeries, to then be told, ‘Yeah, but you're still a man,’ is deliberately and intentionally cruel.”

The ruling has brought back the already polarised national debate over trans rights. However, the Supreme Court justices emphasised that trans people remain protected under the Equality Act against discrimination and harassment.