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 ].