Even though the initial announcement of him scoring Episode VII mentioned him doing the trilogy, until now it wasn’t known if John Williams would return for Episode VIII.
Williams is being presented with the AFI Lifetime Achievement Award, and Variety has a profile on him. Towards the end he confirms that he will be scoring Spielberg’s Ready Player One before moving on to do Star Wars Episode VIII:
“He plans to begin work on Spielbergâ€™s next film, â€œReady Player One,â€ in November, and then next year expects to do the next â€œStar Warsâ€ film. â€œIf I can do it, I certainly will. I told Kathy Kennedy Iâ€™m happy to do it, but the real reason is, I didnâ€™t want anybody else writing music for Daisy Ridley,â€ he quips.”
It’s definitely a good sign that he wants to do it. They recorded Episode VII in Los Angeles to help work with Williams’ heath issues, so there’s probably no reason why Lucasfilm would say no to him if he wants to continue his scores for the rest of the trilogy.