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Anthropic (Claude API)

The API for Claude — Anthropic's LLM focused on safety, reasoning, and coding. Claude excels at long-context understanding, nuanced writing, and code. The API supports function calling, vision, and prompt caching. A strong alternative to OpenAI.

Created by

Dario Amodei, Daniela Amodei, et al. · Co-founded Anthropic in 2021

Website
When to use
  • When Claude's strengths fit (coding, long docs, safety).
  • Long-context tasks (200K tokens).
  • When you want a strong alternative to OpenAI.
  • Tool use / function calling.
When not to
  • When you need a specific OpenAI feature.
  • When cost is the only factor (compare pricing).
  • When you need a non-Claude model.

Definition

The Anthropic API provides access to Claude models (Haiku, Sonnet, Opus). Chat API with messages, (tool use), vision, prompt caching (reduce cost for repeated contexts), and extended thinking (reasoning). Streaming support.

Why it exists

To provide an LLM API focused on safety, reliability, and capability — particularly strong at long documents, coding, and nuanced reasoning.

How it works

POST to api.anthropic.com with x-api-key. Messages array (system, user, assistant). Models: claude-sonnet-4-20250514, claude-opus-4, claude-haiku. Tools for . Prompt caching to reduce repeated context cost. Vision: send images.

Scaling limits

Pay per token. Rate limits. API differences from OpenAI (migration effort). Fewer model options (Claude only).

Cost shape

Pay per token. Claude Haiku is cheapest (~$0.25/1M). Sonnet mid (~$3/1M). Opus most (~$15/1M). Prompt caching reduces cost for repeated context.

Alternatives

  • OpenAI (GPT) — Bigger ecosystem, different strengths.
  • Google (Gemini) — Different model, Google integration.
  • Ollama (local) — Free, private, lower quality.

Failure modes

  • Cost.
  • Rate limits.
  • API migration effort.
  • Fewer model choices.

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