With Total War: Warhammer, Creative Assembly designed a trio of games, each with their own bespoke campaigns, but the core of the series quickly became the mode now known as Immortal Empires—every single faction and lord in one massive sandbox. And that's been a big inspiration for Total War: Warhammer 40,000.
At Gamescom 2026, battle product owner Dave Petry told me that the plan was to make the initial release of Total War 40k the "bedrock" upon which Creative Assembly will continue to build, rather than splitting it up into a trilogy.