The lawsuit filed in San Francisco federal court names OpenAI and its CEO, Sam Altman, as defendants.
It is seeking damages to cover what the province has and will spend on its recovery from the February attack, as well as an order directing changes to the way the company handles ChatGPT conversations that could lead to violence.
Nine people, primarily children, were killed in the school shooting in Tumbler Ridge, British Columbia.
The shooter, Jesse Van Rootselaar, had been flagged by the company's safety team after her conversations about gun violence, but the company did not alert police.
Altman published a letter to the community, saying he was "deeply sorry" OpenAI had not contacted law enforcement.
He promised reforms, but never followed through, despite efforts from British Columbia's attorney general to engage, the lawsuit says.
The school where the shooting took place is in the process of being demolished, and the province has been forced to absorb the costs of a replacement school, mental health care and other effects of the shooting, according to the lawsuit.
Drew Pusateri, a spokesperson for OpenAI, called the Tumbler Ridge shooting an unspeakable tragedy.
"OpenAI remains committed to working collaboratively with government and law enforcement officials, and continuing to advance our ongoing safety work," Pusateri said.
British Columbia's lawsuit comes after more than 30 family members of victims and others impacted by the attack filed lawsuits in California federal court, accusing the company of opting out of a chance to prevent the shooting.
Van Rootselaar shot her mother and stepbrother at home before killing an educational assistant and five students aged 12 to 13 at her former school on February 10. Van Rootselaar, who was 18, then died by suicide.
Van Rootselaar's interactions with ChatGPT were first flagged by the company in June 2025.
Safety team members recommended contacting the police, but Altman and other OpenAI leadership overruled them, the lawsuit says, citing OpenAI whistleblowers who spoke to the Wall Street Journal in the wake of the shooting.
The shooter's account was deactivated, but she was able to get a new account and continue using the platform to plan her attack.
Following publication of the Wall Street Journal article, the company said the account was flagged by systems that identify "misuses of our models in furtherance of violent activities" but the issues did not meet its internal criteria for reporting to law enforcement.
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