Sonia Friedman may just be the most prolific and powerful theater producer working today.

Over the past 30 years, she has become a peerless figure in the West End, where last year she had a record-setting seven shows running simultaneously, and on Broadway, where she has produced five of the past six Tony Award winners for best play. She has been entrusted both with prestige work by celebrated writers like Tom Stoppard and Stephen Sondheim and with stage adaptations of hugely valuable intellectual property like “Harry Potter,” “Stranger Things” and “Paddington.”

But she’s endlessly restless. Taking for granted neither the sustainability of the business nor the security of her own place in it, she has become ever more worried about the industry’s future.

A lifelong Londoner, Friedman spends about one-third of each year in New York, but she hasn’t bought an apartment, and only in January started renting, after decades of hotel stays.

“I live, literally, with a suitcase in the hall,” she said during one of several interviews. “It could all end tomorrow here. It could all end tomorrow there. And it might. It really might. That’s always how I work. The drive is: It could all end tomorrow. It’s not necessarily a nice way to live, is it?”

For years she has expressed concern about the high costs of producing on Broadway, particularly when compared to the West End, but her concern has intensified since the pandemic, as rising costs for labor, materials and services have driven show budgets — and ticket prices for hot shows — ever higher. She said, for example, that “The Hills of California,” a family drama by Jez Butterworth that she produced last year in both cities, faced production costs that were 350 percent higher in New York than in London.