Claude is an AI assistant built by Anthropic. It can write code, analyze documents, reason through complex problems, and use tools. Many developers now use Claude as their primary AI coding tool.
But what exactly is Claude? How is it different from ChatGPT or Gemini? And why should you care as a developer?
This article answers those questions. It is the first article in our Claude AI — From Zero to Power User tutorial series. By the end of this series, you will know how to use Claude’s API, build agents, and work with advanced features like tool use and the Model Context Protocol (MCP).
Let’s start with the basics.
What is Claude?
Claude is a family of large language models (LLMs) created by Anthropic. Anthropic was founded in 2021 by former OpenAI researchers, including Dario and Daniela Amodei.
Claude is not a single model. It is a family of models with different sizes and capabilities:
- Opus — The most powerful model. Best for complex reasoning, large codebases, and multi-step tasks.
- Sonnet — The balanced model. Great performance at a lower cost. Good for daily coding and production use.
- Haiku — The fastest and cheapest model. Best for classification, extraction, and high-volume tasks.
As of 2026, the latest models are Opus 4.6, Sonnet 4.6, and Haiku 4.5.
Anthropic reached over $1 billion in annualized revenue by late 2025. The company is valued at over $60 billion. Claude is one of the most widely used AI assistants in the world.
A Brief History of Claude
Claude has evolved quickly:
| Year | Release | What Changed |
|---|---|---|
| 2023 | Claude 1 | First public release |
| 2024 | Claude 3 (Opus, Sonnet, Haiku) | Three-tier model family, vision support |
| 2024 | Claude 3.5 Sonnet | Major coding improvement |
| 2025 | Claude 4 family | Tool use, extended thinking, computer use |
| 2025 | Claude Code | Terminal-native AI coding assistant |
| 2025 | Agent SDK | Build agents with the same tools Claude Code uses |
| 2026 | Opus 4.6 | 1M context window (beta), Agent Teams, adaptive thinking |
| 2026 | Sonnet 4.6 | First Sonnet to match previous Opus in coding benchmarks |
Each generation brought significant improvements in coding, reasoning, and tool use capabilities.
What Can Claude Do?
Claude is a general-purpose AI, but developers use it for specific tasks. Here is what Claude can do well:
Write and Review Code
Claude can write code in most programming languages. It handles Python, TypeScript, Rust, Go, Java, Kotlin, Swift, and many more. It can also review code, find bugs, suggest improvements, and explain complex code.
Analyze Documents and Images
Claude supports vision. You can send images (PNG, JPEG, GIF, WebP) to the API. Claude can read screenshots, analyze charts, extract data from documents, and describe images. You can send up to 100 images in a single API call.
Reason Through Complex Problems
Claude is strong at multi-step reasoning. It can break down complex problems, think through them step by step, and arrive at correct answers. The extended thinking feature lets you give Claude a “thinking budget” so it reasons more carefully.
Use Tools and Browse the Web
Claude can call functions you define (tool use), search the web for current information, and interact with external services through the Model Context Protocol (MCP).
Build Agents
With the Agent SDK, you can build AI agents that plan, execute, and iterate. These agents use the same tools that power Claude Code — file editing, terminal commands, and web search.
What Claude Cannot Do
It is important to know the limits:
- Cannot generate images. Claude is text and vision input only. It can analyze images but not create them.
- Cannot run code natively. Claude writes code but does not execute it (unless you use Claude Code or tool use to enable execution).
- Cannot access the internet without tools. The base API does not have internet access. You need to enable the web search tool or use MCP.
- Cannot remember between conversations. Each API call is independent. Claude has no built-in memory across sessions (though you can build this yourself).
Where to Use Claude
There are three main ways to use Claude:
1. claude.ai (Chat Interface)
The web and mobile app at claude.ai. Free tier available, with Pro ($20/month) and Max ($100-200/month) plans for more usage.
Best for: Quick questions, document analysis, brainstorming.
2. Claude API (Build Applications)
The API at platform.claude.com. Pay per token. Use the Python or TypeScript SDK.
Best for: Building AI-powered applications, automating workflows, integrating Claude into your products.
3. Claude Code (Terminal)
A command-line tool that works in your terminal. It reads your codebase, edits files, and runs commands.
Best for: Coding, debugging, refactoring, code reviews.
Claude vs ChatGPT vs Gemini
Here is an honest comparison of the three major AI assistants as of early 2026:
| Feature | Claude | ChatGPT | Gemini |
|---|---|---|---|
| Best at | Coding, reasoning, long documents | General knowledge, plugins, image generation | Multimodal, Google integration |
| Context window | 200K (1M beta*) | 128K tokens | Up to 2M tokens |
| Coding benchmarks | Opus 4.6: 80.8% SWE-bench | GPT-4o: ~70% SWE-bench | Gemini 2.5 Pro: ~75% SWE-bench |
| Image generation | No | Yes (DALL-E) | Yes (Imagen) |
| Web search | Built-in tool (API) | Built-in | Built-in |
| CLI tool | Claude Code | None (third-party only) | Gemini CLI |
| Agent SDK | Yes (Python + TypeScript) | Agents SDK | ADK |
| API pricing (input) | $3-5/MTok | $2.50-5/MTok | $1.25-2.50/MTok |
| Safety approach | Constitutional AI | RLHF | Safety filters |
*1M context requires Tier 4 API access ($400+ deposit). Requests over 200K tokens cost 2x input and 1.5x output.
When to choose Claude:
- You need the best coding AI
- You work with large codebases (1M context)
- You want a terminal-native coding tool (Claude Code)
- You are building AI agents
- You value safety and alignment
When to choose ChatGPT:
- You need image generation
- You want the largest plugin ecosystem
- You need general-purpose chat
When to choose Gemini:
- You are deep in the Google ecosystem
- You need the longest context window (2M tokens)
- You want lower API pricing
Use Cases for Developers
Here are the most common ways developers use Claude:
Code Generation and Refactoring
Ask Claude to write functions, refactor code, or convert between languages. Claude Code makes this especially easy — it reads your entire codebase and makes changes in place.
Code Review
Claude can review pull requests, find bugs, suggest improvements, and check for security issues. You can automate this with the API or use Claude Code’s /review command.
Document Analysis
Send PDFs, images, or long documents to Claude. It can summarize, extract key information, answer questions, and generate structured data from unstructured text.
Data Extraction and Classification
Use Haiku for high-volume tasks like classifying support tickets, extracting entities from text, or parsing log files. At $1 per million input tokens, it is very cost-effective.
Building AI Agents
The Agent SDK lets you build agents that plan and execute multi-step tasks. These agents can edit files, run commands, search the web, and call your own tools.
Pricing Overview
Claude offers several pricing options:
Chat Plans (claude.ai)
- Free — Limited usage, Sonnet only
- Pro — $20/month, more usage, all models
- Max — $100-200/month, highest usage limits
API Pricing (Per Million Tokens)
| Model | Input | Output |
|---|---|---|
| Opus 4.6 | $5.00 | $25.00 |
| Sonnet 4.6 | $3.00 | $15.00 |
| Haiku 4.5 | $1.00 | $5.00 |
The API also offers cost optimization features:
- Prompt Caching — Reuse processed prompts at 10% of the input cost
- Batch API — 50% discount for non-time-sensitive workloads
- Model selection — Haiku costs 5x less than Opus
We will cover pricing and cost optimization in detail in Article 4: Understanding Models.
Safety and Alignment
Anthropic takes a unique approach to AI safety. They use Constitutional AI (CAI), where Claude is trained to follow a set of principles rather than relying only on human feedback.
This means Claude:
- Refuses harmful requests
- Is transparent about its limitations
- Avoids generating misleading content
- Follows instructions while staying within safety boundaries
For developers, this means Claude is reliable in production. It is less likely to produce harmful or unexpected output compared to less safety-focused models.
What You Will Build in This Series
This is the first article in a 25+ article series. Here is what we will cover:
Getting Started (Articles 1-6)
- What is Claude (this article)
- Getting Started — API Key, First API Call
- Claude Code CLI — Installation and Setup
- Understanding Models — Opus vs Sonnet vs Haiku
- Prompt Engineering Basics
- CLAUDE.md — Project Instructions
Core Features (Articles 7-12)
- Messages API Deep Dive
- Tool Use (Function Calling)
- Vision — Image Analysis
- Structured Output and JSON Mode
- Extended Thinking
- Prompt Caching and Cost Optimization
Advanced (Articles 13-19)
- Streaming
- Web Search and Citations
- MCP — Model Context Protocol
- Building MCP Servers
- Computer Use
- Agent SDK
- Agent Teams
Real Projects (Articles 20-25)
- Build a Code Review Bot
- Build a Document Processing Pipeline
- Build a Multi-Agent System
Every article includes working code in both Python and TypeScript.
What’s Next?
In the next article, we will set up your development environment, get an API key, and make your first API call to Claude.
Next: Getting Started — API Key, First API Call, SDKs