Claude API in Production: The Complete Developer Guide (2026)

The Claude API is genuinely different from OpenAI's API in ways that matter for production applications. Having shipped products on both, here's the practical guide I wish existed when I started. The Model Lineup As of 2026, the main Claude models: Model Speed Cost Best For claude-haiku-4-5 Fastest Lowest Classification, simple extraction claude-sonnet-4-6 Balanced Mid Most production tasks claude-opus-4-6 Slowest Highest Complex reasoning, agentic tasks Start with Sonnet. Upgrade to Opus only if quality isn't sufficient. Drop to Haiku for high-volume, low-complexity tasks. Basic Setup npm install @anthropic-ai/sdk import Anthropic from "@anthropic-ai/sdk" const client = new Anthropic({ apiKey: process.env.ANTHROPIC_API_KEY, }) The Messages API const response = await client.messages.create({ model: "claude-sonnet-4-6", max_tokens: 1024, messages: [ { role: "user", content: "Explain async/await in one paragraph." } ], }) const text = response.content[0].type === "text" ? response.conten