DeepSeek

DeepSeek is a free chat assistant on the web and mobile from the Chinese lab of the same name. It runs DeepSeek's own open-weight models, offers a deep-thinking mode for math and code, and has no paid consumer plan.

The app supports web search, file uploads and a reasoning mode that shows its chain of thought before the final answer. It is popular with students and developers who want strong reasoning without a subscription.

Because the company is based in China, some governments and companies restrict its use on work devices. Developers who want the same models in their own apps can use the separate DeepSeek API or self-host the open weights.