Both the player and Manchester City have finalised the move, according to reports in Chile.
The 28-year-old enjoyed the season of his career with the Gunners, culminating with FA Cup glory at Wembley.
But failure to challenge for the title has led to speculation over whether the former Barcelona forward would extend his stay at the Emirates with just one year remaining on his deal.
With moves to City, Chelsea and Bayern Munich rumoured, much-respected Chilean journalist Fernando Solabarrieta dropped the bombshell that Guardiola has won out for the player.
In a 1-1 draw with Russia ahead of the Confederations Cup, Sanchez supplied a superb assist for former QPR wing-back Mauricio Isla to break the deadlock.
Arsene Wenger has maintained that times have changed and that Arsenal simply do not need to sell their best players any more.
Even if that changes, the Gunners will be loath to send their star man to a domestic rival as they bid to build on their cup success in the first of Wenger’s new two-year deal.