Once Spotify's most visible critic, pop superstar Taylor Swift on Friday returned her music to all streaming services as the number of artists to boycott the booming format dwindles.

All of the 27-year-old singer's music including "1989," her blockbuster last album, appeared on Spotify and other platforms at midnight (0400 GMT) on the US East Coast.

Swift's management said the move was meant to mark "1989" hitting 10 million sales worldwide and certification that the teen country music prodigy turned pop sensation had sold 100 million singles in the United States.

"Taylor wants to thank her fans by making her entire back catalog available to all streaming services," it said in a statement.

When she released "1989" in late 2014, Swift refused to put it on Spotify, by far the largest streaming service, and yanked her entire catalog off it.

Swift accused Spotify of devaluing artists by essentially giving music away for free, pointing to the platform's advertising-backed tier that gives access to non-subscribers.

The feud brought a defensive reaction from the Swedish company which argued that it was a rare source of growth in the long-beleaguered music industry.

Spotify says it paid back $5 billion to songs' copyright holders as of September 2016, the last time it updated the figure it had given in response to Swift.

- More bad blood with Katy Perry? -

But much has changed even in the two and a half years since Swift's row with Spotify.

Streaming -- which offers unlimited, on-demand music online -- has soared, led by a growth in paid subscriptions.

Streaming revenue grew worldwide by more than 60 percent last year alone, according to the IFPI trade body. 

Most other major Western artists who refused to stream their music have relented, including the estates of late pop icon Prince and The Beatles, rock legend Neil Young and country music giant Garth Brooks.

But the timing of Swift's return to streaming services raises eyebrows -- her music went online at the exact moment that fellow pop mega-star Katy Perry released her new album "Witness."

The two artists have a barely concealed rivalry. Perry's latest album features the song "Swish Swish" in which she boasts of her success to a rival -- presumably Swift -- accused of bad-mouthing her.

Swift's move could potentially hurt Perry in closely watched first-week sales. With significant overlap between their fan bases, some listeners who would have played "Witness" on repeat may spend time exploring Swift's music on Spotify instead.

- Already with Apple -

Swift's decision also marks a realization that physical sales or paid downloads of "1989" have passed their peak so long after the release. 

The only album to sell better than "1989" in the past few years has been British balladeer Adele's "25," which she held off streaming services for seven months.

Despite her hostility to Spotify, Swift allowed "1989" to be streamed on Apple Music from the moment the tech giant launched the service in June 2015. 

Swift had initially threatened to boycott Apple Music over not paying artists for streams by listeners on three-month free trial periods. Apple quickly shifted course after Swift's public reprimand.

While the tech behemoth's about-face was mostly seen as proof of Swift's crushing power, some conspiracy-minded music watchers alleged that the entire drama had been staged for publicity reasons.

Artists who remain firm against streaming their music include English progressive rock pioneers King Crimson, US heartland rocker Bob Seger and experimental metal band Tool.