Official Twitter blog:

Twitter has made the policy decision to off-board advertising from all accounts owned by Russia Today (RT) and Sputnik, effective immediately. This decision was based on the retrospective work we’ve been doing around the 2016 U.S. election and the U.S. intelligence community’s conclusion that both RT and Sputnik attempted to interfere with the election on behalf of the Russian government. We did not come to this decision lightly, and are taking this step now as part of our ongoing commitment to help protect the integrity of the user experience on Twitter.

As the blog mentions, Twitter is taking those funds and redirecting to external research “into the use of Twitter in civic engagement and elections, including use of malicious automation and misinformation, with an initial focus on elections and automation”.