Short answer: the plan you're on matters more than which AI you use.
Free consumer tiers often reserve the right to use your conversations to improve the models — sometimes with a buried opt-out toggle. Paid business and enterprise tiers generally commit to not training on your data, and add controls like retention limits and admin policies. Same company, very different promises.
A workable rule of thumb: on a free consumer plan, paste nothing you wouldn't email to a stranger. Client data, contracts, health records, unreleased numbers — that's business-tier territory, and vendors like Anthropic and Microsoft compete hard on exactly this.
Data sensitivity is one of the five questions in our quiz precisely because it changes the right answer — a tool that's perfect for a hobbyist can be wrong for a consultant with client files.