DeepSeek: complete guide, strengths and limitations

What is DeepSeek? The essentials, explained simply

A simple definition

DeepSeek is a free AI chatbot built by a Chinese company. It can:

• Hold a natural conversation with you
• Write and debug code (this is where it shines)
• Solve logic and maths problems
• Generate text and handle writing tasks
• Answer in English, French and Chinese
• Answer fast in Instant Mode, or take the time to reason in Expert Mode

Who built DeepSeek?

DeepSeek was built by DeepSeek Inc., a Chinese company founded in 2023 by Liang Wenfeng. The company focuses on AI research and on optimizing language models.

What makes it different: DeepSeek publishes its model weights under the MIT license on Hugging Face, which neither OpenAI does for ChatGPT nor Anthropic for Claude.

Is DeepSeek free? What can actually be verified

This is where most guides overreach. Here is what DeepSeek's own official documents state, and what they do not.

What DeepSeek does state:

• The official site presents access to the assistant as free
• The launch announcement for its app described free use, with no ads and no in-app purchases
• The V4 model weights are released under the MIT license

What DeepSeek states nowhere:

• No commitment that it will be free forever. On the contrary, the terms of use reserve DeepSeek's right to add, modify, suspend or terminate its services
• No document mentions an unlimited number of requests on the assistant
• The API is paid and billed per token — and DeepSeek's own pricing documentation warns of an upcoming increase that it describes as significant

What can be explained, on the other hand, is why it is cheap to run: the V4 models are mixture-of-experts architectures. DeepSeek-V4-Pro totals 1.6 trillion parameters but activates only 49 billion of them to answer. You pay for the compute of the activated slice, not the whole model.

DeepSeek models in 2026

What changed: V4 replaces the V3 / R1 pair

If you have read a DeepSeek guide written in 2025, it told you to choose between DeepSeek-V3 for general use and DeepSeek-R1 for reasoning. That split no longer exists.

The official API documentation now lists only two models: deepseek-v4-flash and deepseek-v4-pro. The legacy identifiers deepseek-chat and deepseek-reasoner were retired on July 24, 2026, after a three-month transition period announced in the change log.

More importantly, the "one fast model on one side, one thinking model on the other" dichotomy is gone. Both V4 models handle reasoning internally, through a mode: the documentation describes a non-thinking mode and a thinking mode (enabled by default), with a three-level effort setting — low, high and max — that decides how long the model deliberates. You no longer switch models to get a more considered answer — you switch settings.

deepseek-v4-flash and deepseek-v4-pro: the comparison

API pricing

The consumer assistant is free, but the API is billed. DeepSeek publishes its prices in US dollars, per million tokens. A "cache hit" is the start of a request the system has already seen, re-billed at a much lower rate.

In the app: Instant Mode and Expert Mode

On the consumer side, at chat.deepseek.com and in the mobile app, you do not pick a model identifier. The official V4 announcement points to two modes instead: Instant Mode for an immediate answer, Expert Mode when the model should take the time to reason. It is the same machinery as the API's thinking mode, presented more simply.

How to use DeepSeek: a step-by-step guide

Step 1: open DeepSeek

1. Go to Chat.DeepSeek.com
2. Or install the mobile app from the App Store or Google Play

Step 2: create an account (required)

Contrary to what many guides claim, the account is not optional: DeepSeek's terms of use require you to register before using the service.

1. Click "Sign up" (top right)
2. Enter your email, or sign in with a Google or Apple account
3. Verify your email
4. Your account is created

The upside of an account: your past conversations follow you across every device.

Step 3: ask your first question

1. Click the text box at the bottom
2. Type your question or request
3. Press Enter or click Send
4. Wait a few seconds for the answer
5. Ask a follow-up question if you need to

Step 4: pick the mode (Instant or Expert)

At the top of the conversation you pick a mode, not a model:

• Instant Mode: an immediate answer, for most requests
• Expert Mode: the model reasons before answering, for hard problems

Tip: stay in Instant Mode by default, switch to Expert Mode when the first answer looks rushed or wrong.

Use cases: 20 ways to use DeepSeek

Programming (its specialty)

1. Debug code: paste your code, DeepSeek finds the error
2. Generate code: describe what you want, DeepSeek writes it
3. Optimize code: make it faster and leaner
4. Explain code: understand how a script works
5. Learn to program: personalized tutorials in Python, JavaScript and more

Logic and maths

6. Solve equations: advanced maths
7. Explain concepts: algebra, geometry, statistics
8. Crack puzzles: logic and reasoning
9. Analyze algorithms: complexity, optimization
10. Implement algorithms: sorting, searching, graphs

Writing and content

11. Draft articles: quick first drafts
12. Write emails: professional or personal
13. Generate ideas: fast brainstorming
14. Write documented code: with comments
15. Translate text: between several languages

Learning and education

16. Explain concepts: computer science, maths, science
17. Prepare for an exam: personalized questions and answers
18. Learn a language: conversation practice in English, French and Chinese
19. Do research: a quick summary of a topic
20. Solve problems: step by step

DeepSeek vs ChatGPT: detailed comparison

Full comparison table

When should you pick DeepSeek?

• You want code: DeepSeek is better
• You do not want to pay: the DeepSeek assistant is free
• You handle very large documents: 1 million tokens of context
• You want to self-host the model: the weights are MIT licensed
• You are solving logic problems: DeepSeek is better

When should you pick ChatGPT?

• You want the best writing: ChatGPT is better
• You want to generate images: ChatGPT is better
• You want a massive community: ChatGPT is better
• You want an ecosystem of integrations: ChatGPT is better
• You want a provider outside China: ChatGPT is better

DeepSeek strengths

• A free assistant: DeepSeek advertises free access to its assistant
• 1 million tokens of context: on both V4 models
• Built-in reasoning: a mode to switch on, not a model to swap
• Open weights: MIT licensed, so you can self-host
• Cheap API: from $0.14 per million input tokens
• Excellent at code: this is its recognized specialty
• Web search and file upload: available in the app
• Strong multilingual quality

DeepSeek limitations

• An account is mandatory: you cannot try it without signing up
• No commitment to stay free: the terms let DeepSeek modify or suspend its services
• An announced price rise: on the API, DeepSeek warns of a significant increase
• No image generation: no such feature is announced
• V3 and R1 are no longer served: any integration built on them needs reworking
• Limited Responses API: available on Flash, not yet on Pro — DeepSeek announces it for early August 2026
• Less well known: fewer resources and tutorials
• Hosted in China: weigh this against how sensitive your data is

Tips to use DeepSeek effectively

1. Switch to Expert Mode for complex logic

For hard maths or logic problems, switch to Expert Mode:

• The answer arrives later, because the model reasons first
• This is what replaced the old R1 model
• On the API side, the same effect comes from the thinking mode and its effort setting (low, high, max)

2. Be specific in your requests

Vague: "Write some code"

Specific: "Write a Python script that reads a CSV file and counts the rows with a price above 100 euros"

3. Give it context

Without context: "Fix this code"

With context: "Fix this Python code. Error: 'list index out of range' on line 15"

4. Play to its strength: code

DeepSeek excels at programming. Use it to:

• Debug code
• Generate code
• Optimize algorithms
• Explain complex code

5. Iterate and improve

Just like with ChatGPT, ask follow-up questions:

• "Make it faster"
• "Add comments"
• "Explain this line"
• "Optimize memory usage"

6. Check the facts

DeepSeek can "hallucinate" too (invent information). Always check:

• Statistics
• Dates
• Library names
• Programming syntax

7. The account is mandatory, so put it to work

Signing up is not optional, as we saw above. Once the account exists, it lets you:

• Save your conversations
• Get back to your history
• Sync across devices

FAQ: frequently asked questions about DeepSeek

Conclusion: DeepSeek in 2026

DeepSeek in 2026 is no longer the V3 / R1 pair that most guides still describe. It is a two-model line-up, deepseek-v4-flash and deepseek-v4-pro, both of which reason on demand and share a one-million-token window.

Ideal use cases

• Programming: debug, generate and optimize code
• Logic and maths: solve complex problems
• Writing: articles, emails, content
• Learning: tutorials, explanations, concepts

Next steps

1. Open DeepSeek: Chat.DeepSeek.com
2. Create your account: it is the prerequisite, not an option
3. Ask your first question: get a feel for the interface in Instant Mode
4. Run it again in Expert Mode: you will see the difference on a hard problem
5. Compare it with ChatGPT: find your favorite

Final recommendation: use DeepSeek for code and ChatGPT for writing. Each offers free access to its assistant, and they are complementary.

To dig into the other side of that pairing, read our complete ChatGPT guide.

Ready to try DeepSeek?