Brand voice stays consistent with AI when you give the model explicit references — real past copy, a defined vocabulary, sentence-length preferences, and a list of phrases to avoid — rather than a generic one-line tone description. Most drift happens because teams under-specify voice and then blame the tool when output feels off-brand.
Build a living style guide the AI tool references every time, review output against it regularly, and update the guide as the brand evolves rather than treating it as a one-time setup. A human editor checking the first output batch closely, then spot-checking after, catches drift before it compounds.