Why do some AI writing tools charge per word while others have unlimited plans?

AI writing tools charge per word because every generation costs them real money in computing power, while unlimited plans spread that cost across users who write less. Think of it like a gym membership. The gym bets that most people won't show up every day. Unlimited AI plans work the same way — they're counting on the fact that most subscribers won't max out their usage. Per-word pricing is more common with tools built directly on OpenAI's API, like Jasper or Copy.ai in their early days. Every time you hit 'generate,' the tool pays a tiny fee to the underlying AI model. Those fractions of a cent add up fast. Unlimited plans, like what Rytr offers on its $29/month premium tier, work because Rytr uses a mix of its own fine-tuned models and caps generation length per click. You can generate all month, but each output is relatively short. I've seen writers get frustrated when they realize 'unlimited' doesn't mean 'generate a 2,000-word article in one go.' It usually means lots of smaller generations. The real question isn't which pricing model is better — it's how you actually write. If you generate short social posts all day, unlimited plans shine. If you need long-form drafts, per-word pricing might actually be cheaper. For a completely different approach, see our guide on AI content generators that work without prompts. **Related**: Which AI writing tool is cheapest for long-form blog posts? | How do AI writing credits actually work?