Deutsche Telekom AG is in talks about a potential offer for SoftBank Group Corp.’s 8.5% stake in T-Mobile U.S. Inc., a deal that would give the German telecom giant greater control over its U.S. affiliate.

The terms of a potential deal, including whether Deutsche Telekom might bid for the entire stake to get majority control, haven’t been finalized and no firm decision has been made about an offer, according to people familiar with the matter, who asked not to be identified because the talks are private. Deutsche Telekom Chief Executive Officer Tim Hoettges may reveal plans to expand the company’s U.S. presence at a capital markets day this week, one of the people said.

Representatives for Deutsche Telekom and SoftBank declined to comment.