Britney Spears and Sin City aren't breaking up just yet ... she's decided to extend her residency at The Axis in Planet Hollywood for another two years.
Brit made the announcement Wednesday night during her "Britney: Piece of Me" show.
As TMZ first reported, Brit's initial deal called for her to make $30 million over two years, but the show performed so well ... she quickly negotiated herself a pay bump.
The extension will give her 4 years on the Strip -- shy of Elvis Presley's 7-year run, but still impressive by today's standards.
Fun fact: Elvis got a staggering $500,000 just for his initial 4 weeks in Vegas ... in 1969!