News Analysis Current chatbots aren't likely to help lone actors invent a deadly pathogen, experts say. But newer models, trained in biology, may need stronger safeguards. The threat of biological weapons has hung over the world for decades now. Sept. 14, 2026, 5:02 a.m. ET Among the growing fears about artificial intelligence, one threat has proved particularly alarming: the possibility that A.I. could be used to create a new wave of biological weapons. In April, biosecurity experts warned that it was disturbingly easy to get advice from chatbots about making pathogens more dangerous. In June, scientists and A.I. executives signed an open letter calling for new controls on the fabrication of DNA because A.I. can now speed up the design of toxins and viruses. In August, scientists reported that they had used A.I. to build viruses not seen in nature. And on Thursday, Anthropic announced that it had blocked several attempts to use its models by people who might have been trying to weaponize pathogens. Dario Amodei, the chief executive of Anthropic, followed up with a call on Saturday to slow down the development of A.I., with a set of proposals to keep it safe. It would be wise, Dr. Amodei wrote, to ban "using AI for the production of biological weapons or allowing users to do so."

These developments may give the impression that bad actors can now unleash previously unknown plagues on the world, all thanks to A.I. But Drew Endy, a synthetic biologist at Stanford University who coauthored a report on biosecurity last year, said that current chatbots, like Anthropic's Claude, don't represent a sea change in the threat posed by biological weapons. "In terms of the net impact on our biosecurity risk right now, I find it to be modest," he said. That could change, he added, as scientists develop A.I. models specializing in biological research. Already these models can generate genomes for viable viruses not found in nature. It's conceivable that the models may eventually be able to use those new genomes to create new weapons. A biological weapon can be a virus or another pathogen, such as bacteria or fungi, that is designed to be unleashed against armies or civilians. Or it can take the form of toxins produced by organisms, such as botulinum from bacteria or ricin from castor plants.

(Biological weapons are distinct from chemical weapons, such as nerve gas, which scientists synthesize in labs.) As far back as the Middle Ages, armies tried using disease as a weapon. In 1346, the Mongols loaded the bodies of people who died from bubonic plague onto catapults and launched them into the city of Caffa on the Black Sea. Five centuries later, after scientists developed the germ theory of disease, those efforts became more precise. During World War I, German spies sneaked into the United States and other countries with vials of bacteria. They used it to kill thousands of horses and mules. The Geneva Protocol prohibited biological warfare, but the great powers built biological weapons anyway. Eventually, the United States and the Soviet Union held gigantic stocks, from anthrax bombs to balloons loaded with wheat-killing fungi. After signing the Biological Weapons Convention in 1975, the United States destroyed its massive stockpiles but continued studying biological weapons to develop defenses. The Soviet Union secretly carried out more investigations of pathogens, such as smallpox, for a new generation of biological weapons. All of which is to say the threat of biological weapons was very real long before Open AI and Anthropic appeared. And yet as far as is publicly known, biological weapons have caused very few deaths since World War II, for reasons that remain unclear. "We don't know what has been tried and failed, what has been deterred, what was too technologically challenging," said Dr. Thomas Inglesby, the director of the Johns Hopkins Center for Health Security. Image Anthrax, shown here under a microscope, has been stored as a biological wea...