One of Chicago's largest private tech companies is bought by a British private-equity firm. : ThoughtWorks, one of Chicago's largest private companies, is being acquired by Apax, a London-based private equity firm. Terms of the deal weren't disclosed. But ThoughtWorks has about 4,500 employees, including about 200 in Chicago. It did $460 million in sales last year, up 15 percent from 2015, ranking 110th on Crain's list of largest privately held companies. “Apax acquired us for our technical competence, talent and our culture,” a ThoughtWorks spokeswoman said.