My recommendation would be to not use those services. That's not "deal with it", that's "negate their value proposition until they comply with your demands as a consumer".
But if you feel so moved to use the product or service, or must for some reason, well... don't mention that you're thinking about committing a crime.
Also, I'd say that this isn't quite as clear as vacuuming up people's data and handing it off. There's not much money in calling the police on your users. What there is, is reduced liability.
Preface: IANAL.
Let's say the user in the story told Claude (or whatever product of Anthropic's she was using) that she was thinking of attacking law enforcement, and actually carried out the attack. People are injured or killed. Facilities are damaged. She's either arrested or killed. Either way there's an investigation into what happened. Law enforcement looks at her digital footprint and sees that she had mentioned to Anthropic through Claude that she was thinking about committing the crime.
Since there's now loss involved - the health of the survivors, the lives of the dead, and the usability of the facility - there's now a search on how to recoup that loss monetarily. The lawyers file a suit alleging that Anthropic neglected their duty of care to their customers and the community, because supposedly Anthropic's worth hundreds of billions (if not trillions) of dollars and those bastards need to pay.
The typical legal shenaniganning by Anthropic's lawyers doesn't get the suit tossed and it goes to trial. Survivors talk about how their lives have been changed forever, and opposing counsel says it's because those damned tech bros with the data centers and the job-killing AI didn't report the threat to law enforcement. The jury, being made up of people from the general public (who are polling as antagonistic towards AI [0]), agrees. They award damages.
Other lawyers, having case law and a template for victory, smell blood in the water. They put out the "if you or a loved one" ads like they did for asbestos and tobacco companies, but for AI. Individual suits and class-actions are filed.
Now the company is facing potentially billions of dollars in judgments and investors are looking for the exit because, well, there's not any money in paying off legal judgments.
And that's before we take into account any regulations that get passed.
If you're Anthropic's corporate counsel, and you're faced with this possible scenario, you tell their C-suite that you will quite literally lunge over the table and throttle them if they don't implement a policy to inform law enforcement of possible threats found in chats.
[0] https://news.gallup.com/poll/712751/americans-cool-toward.as...