Yuri Milner, the Russian investor known for his bets on Facebook Inc and Twitter Inc, is pulling out of an arrangement that let him invest automatically in a group of companies participating in a program called Y Combinator. The companies will instead receive investments from venture-capital firm Khosla Ventures, Y Combinator said in a blog post on Monday. Milner has been spending less time focused on seed-stage investing, the blog post said. Yuri originally came up with the idea for investing in all YC companies, and were grateful to him for that and for all the years he has participated. A spokesman for Milner did not immediately respond to a request for comment.