‘Spectre’ was the first release from the sessions for Radiohead's ninth LP that had commenced in september 2014. The band wrote and recorded the song after being asked to provide a theme song for the upcoming 24th James Bond film of the same name. Radiohead have had a long-lasting fascination with Bond theme songs, and since they were now writing and recording again anyway following their longest break ever from working collectively, the timing of the request was excellent.
There are currently no details available regarding the sessions for this song, but it is highly likely that the strings were recorded at a session at AIR studios in London. Conducter Robert Ziegler had posted three photos from that session, which also show Thom, Jonny, Ed and Nigel, to his social media accounts in early September 2015, but deleted them a short while later, possibly at the request of the band, who wanted to avoid premature speculation about them doing the new Bond song. Such speculation went around already, and was indeed fuelled by these images (click to enlarge):
Spectre was released in the UK on October 26th 2015, with a theme song by Sam Smith called ‘Writing's On the Wall’. For two months after that it was still unclear if Radiohead had actually produced a theme song of their own, or whether the rumours from the period leading up to the film's release had been unfounded. They were not, as was shown when Radiohead in a surprising move released their rejected (or withdrawn) Spectre theme song on December 25th 2015 as a download-only single on Soundcloud:
Thom wrote a few words on Twitter on the day of the release, but left the reasons why the song wasn't used in the movie open to speculation:
This was Radiohead's first release since The Daily Mail/Staircase in December 2011 - a break of almost exactly four years, the longest since the band signed to EMI in 1992.