Microsoft Corp. dropped a nearly decade-long legal battle with European regulators Oct. 22, agreeing to key parts of an antitrust ruling that has already led to hundreds of millions in fines.

The world’s largest software company will slash the royalty fees it charges rivals for critical interoperability information needed to make programs that work smoothly with Microsoft’s ubiquitous Windows. It will broaden access for open source developers that the EU said are now “virtually the only alternative for users.”