She parted with him after the 2013 season in order to find a full-time coach. Nainkin had also been working with fellow American Sam Querrey that year. Stephens replaced him with Paul Annacone, who is better known for coaching two of the greatest players in tennis history in Pete Sampras and Roger Federer. She became the first woman to be coached by Annacone. Although the pair worked well together, Stephens split with Annacone in late 2014 after not matching the success from her previous year that season. Stephens briefly worked with Thomas Högstedt in late 2014. At the start of 2015, she returned to her longtime junior coach, Nick Saviano. While working with Saviano, Stephens won her first WTA title, but did not manage to ascend back up the WTA rankings. In the 2015 offseason, she replaced him with Kamau Murray. With Murray as her coach, Stephens established herself as one of the best players in women's tennis. She has since won five of her six titles, including three in 2016, her first major at the 2017 US Open, and her first Premier Mandatory title in 2018. She has also reached a new career-high ranking at No. 3 in the world. Stephens split with Murray during the 2018 offseason before reuniting with him in August 2019 shortly before the US Open. In Murray's absence, Stephens had worked with Sven Groeneveld for three months. Stephens is represented by TLA Worldwide. She has been sponsored by Nike since the start of 2018. Her clothing sponsor had previously been Under Armour since 2010. Stephens uses Head rackets, specifically the Graphene XT Radical Pro model as of 2018. Following her US Open victory, Stephens accrued several new sponsors, including the automobile manufacturer Mercedes-Benz. She has also appeared in television advertisements for Built with Chocolate Milk, a campaign to encourage chocolate milk as a recovery drink. Her other health-related endorsements include doTerra, Precision Nutrition, and Colgate. doTerra is a company that primarily sells essential oils, while Precision Nutrition provides coaching for diet and exercise. With Colgate, Stephens is a part of their Bright Smiles, Bright Futures campaign that focuses on educating children about oral hygiene. Stephens has previously signed a deal with the American Express credit card company and was formerly an endorser of the Listerine mouthwash product. She was also a brand ambassador for USANA, a nutrition company. Moreover, Stephens has worked with Time Warner Cable as part of their Connect a Million Minds campaign to motivate the importance of education in science, technology, engineering, and math (STEM) fields.