From an interview with The Guardian newspaper at the Hay Literary Festival on May 25 2007:
Banks tells me that he has spent the past three months writing another Culture novel. It will be called Matter and is to be published next February. “It’s a real shelf-breaker,” he says enthusiastically. “It’s 204,000 words long [544 pages, according to Amazon] and the last 4,000 consist of appendices and glossaries. It’s so complicated that even in its complexity it’s complex. I’m not sure the publishers will go for the appendices, but readers will need them. It’s filled with neologisms and characters who disappear for 150 pages and come back, with lots of flashbacks and -forwards. And the story involves different civilisations at different stages of technological evolution. There’s even one group who have disappeared up their own fundaments into non-matter-based societies”.