Many psychologists and psychiatrists have shared the vision, noting that fewer than half of people with a mental disorder receive therapy, and those who do might get only 45 minutes per week. Researchers have tried to build tech so that more people can access therapy, but they have been held back by two things. One, a therapy bot that says the wrong thing could result in real harm. That's why many researchers have built bots using explicit programming: The software pulls from a finite bank of approved responses (as was the case with Eliza, a mock-psychotherapist computer program built in the 1960s). But this makes them less engaging to chat with, and people lose interest.

On a hot afternoon in June, I downloaded a free mental health app called Woebot. I was feeling somewhat worn out and anxious from too many hours reading news about the double pandemic of Covid-19 and systemic racism, and the hubris of too quickly reopening the country. Woebot claimed it could help. "I'm an emotional assistant," Woebot explained, after asking about my mood, which was sluggish and pessimistic. "I'm like a wise little person you can consult with during difficult times, and not so difficult times."