Quick Answer
Consumer tiers may. API and enterprise tiers typically don't. Check settings.
Detailed Answer
Each AI handles data differently: ChatGPT uses conversations by default (opt-out available). Claude doesn't train on conversations but may use feedback. Gemini stores data for improvement. All offer API access where data isn't used for training. Enterprise plans universally guarantee no training. Always check privacy settings and consider API access for sensitive work.
Find Your Own Answer
The best way to decide is to try them yourself. Council lets you compare multiple AI responses to the same question.