He told BBC Radio 4’s Today programme the technology had been used to “extricate” John Lennon’s voice from an old demo so he could complete the song. “We just finished it up and it’ll be released this year,” he explained. Sir Paul did not name the song, but it is likely to be a 1978 Lennon composition called Now And Then. It had already been considered as a possible “reunion song” for the Beatles in 1995, as they were compiling their career-spanning Anthology series.
Source: Sir Paul McCartney says artificial intelligence has enabled a ‘final’ Beatles song