Choose ChatGPT, Claude, or Gemini as the default script engine — one primary, one backup login, not three competing styles. Lock a prompt template: voice-of-customer quotes, four beats (hook, problem, demo, CTA), 75–95 spoken words for a 30-second cut, three hook variants, banned claims. Scripts leave this layer as text. They do not leave it as a half-rendered video.
The LLM is cheaper and more inspectable than a black-box 'ad generator' that hides the script inside a credit burn. You want to edit the line, run a read-aloud, and check claims before a face exists. That is why the language model sits upstream of the renderer. Switching models weekly because of Twitter benchmarks is how your tone drifts and your banned-claim list gets ignored. Pick the one your team will actually paste a review corpus into. Pay for the plan that lets you keep a project or a custom GPT/Gem with the claims list loaded.
Do not buy a second 'copy AI' that also writes emails, PDPs, and LinkedIn carousels unless that is a different team's stack. Performance creative needs a short, vicious template, not a content studio. If a strategist wants a research model and a writer wants a prose model, that is still one slot with two logged-in tools — not six SEO writers and a tagline mill. Output of this layer: a locked body, three hooks, a claims pass. Nothing else ships downstream.