The Verizon subsidiary that housed Yahoo and Tumblr after Verizon’s 2017 acquisition of Yahoo was Oath.
Verizon completed its purchase of Yahoo’s operating business in June 2017. Rather than placing Yahoo and Tumblr directly under the Verizon brand, it combined them with AOL and other internet properties inside a new subsidiary called Oath. Oath therefore became the corporate umbrella associated with Tumblr during the 2017–2019 period.
A common mix-up is confusing Oath with AOL. AOL was one of the businesses brought into the Oath structure, not the name of the post-acquisition parent that housed both Yahoo and Tumblr. Oath was renamed Verizon Media in 2019, after Verizon sold Tumblr to Automattic, the company behind WordPress.com.
The corporate chain can be summarized as Tumblr joining Yahoo in 2013, Yahoo moving under Verizon through the 2017 acquisition, and Tumblr then operating within Oath. That history explains why contemporary reports often described Tumblr as a Verizon-owned or Oath-owned service.