What is DeepSeek? Definition, models and how it works

How does DeepSeek work?

DeepSeek works as a family of open-weight language models served through a chat app and a paid API. Users talk to the models at chat.deepseek.com or in the mobile apps, while developers call them through an API that follows the OpenAI request format. Since January 2025 DeepSeek publishes its model weights under free licences (MIT for R1-0528, V3.1, V3.2 and V4), so anyone can download and run them on their own servers.

The models use a Mixture-of-Experts architecture. According to the DeepSeek-V3 technical report, V3 has 671 billion parameters in total but activates only 37 billion per token, and it was trained on 14.8 trillion tokens using 2.788 million H800 GPU hours. This design is the main reason DeepSeek is cheap to train and cheap to run compared with dense models of similar quality.

DeepSeek history: key dates

DeepSeek grew from High-Flyer’s internal AGI research lab into one of the most watched AI labs in the world in under two years.

The Nature paper also answered the cost debate. Its supplementary material puts the reasoning training of R1 at about 294,000 USD, on top of roughly 6 million USD spent on the base model, according to Scientific American’s report on the publication.

DeepSeek models and API pricing

DeepSeek currently sells two main models through its API, Flash and Pro, both with a 1 million token context window. The overview below uses DeepSeek’s own pricing page (October 2026, peak rates per 1 million tokens).

DeepSeek Flash

Flash (DeepSeek-V4.1-Flash) is the fast, low-cost model: 0.30 USD per million input tokens on a cache miss and 1.20 USD per million output tokens. Off-peak rates are half of that.

DeepSeek Pro

Pro (DeepSeek-V4-Pro) targets harder reasoning and coding tasks at 1.32 USD per million input tokens and 3.96 USD per million output tokens. Both models allow up to 384,000 output tokens.

DeepSeek in marketing, SEO and AI search

For marketers, DeepSeek matters more as a cheap engine inside tools than as a place where customers search. Statcounter’s September 2026 data gives DeepSeek only 0.02% of the worldwide AI chatbot market, against 80.48% for ChatGPT and 10.91% for Google Gemini. Brand visibility work for Generative Engine Optimization should therefore focus on ChatGPT, Gemini and AI Overviews first.

Where I do see DeepSeek in SEO work is behind the scenes: content briefs, keyword clustering, translation drafts and data extraction at a fraction of the price of closed models. Because the weights are open, agencies can host a large language model on their own infrastructure and keep client data out of third-party clouds.

Privacy and regulation

DeepSeek’s consumer app stores user data on servers in China, which triggered action from European regulators. Italy’s Garante blocked the app on 30 January 2025, and Poland’s UODO advised far-reaching caution on 6 February 2025. Use the hosted app only for non-sensitive tasks, and self-host the open weights when client or personal data is involved.

DeepSeek vs ChatGPT

Other open alternatives include Mistral AI from France, which is the safer choice for teams that need EU data residency.

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