ModelRefs / Anthropic API — AI Glossary
Anthropic API — AI Glossary
Anthropic's cloud API providing access to Claude models with the Messages API, tool use, vision, and streaming. 7+).
Overview
The Anthropic Messages API (/v1/messages) supports Claude Haiku, Sonnet, and Opus families. Distinctive features: long context (200K tokens), vision (image input), streaming SSE, tool use (function calling), and extended thinking (Claude 3.7+). Not OpenAI-compatible natively; translation via LiteLLM or Bedrock.
Reference details
| Topic | infrastructure |
|---|---|
| Last reviewed | 2026-06-24 |
Related terms
Example: The system prompt is a field, not a message
The most common porting bug is structural. In the chat completions convention the system instruction is the first element of the messages array with role “system”. Here it is a separate top-level `system` parameter, and messages alternate user and assistant. Code that moves across without changing that either drops the instruction or sends it as a user turn — and the failure is silent, because the request is still valid and the model still answers, just without the constraints you thought you had set. Compatibility layers usually handle the translation; hand-rolled ports frequently do not.
Commonly confused with
It is not natively an OpenAI-compatible endpoint — the request shape, the system-prompt placement and the tool-use format all differ, and compatibility comes from a translation layer such as a gateway. Vendor-hosted deployments add another axis: the same model family reached through a cloud marketplace may differ in available features and region.
When to use it
Reach for it when:
- Direct integrations where you want the native feature surface without translation loss
- Long-context, vision and extended-thinking work, which are first-class here
- Tool use where the native format avoids a lossy conversion
Reach for something else when:
- Dropping into code that assumes the chat completions shape without adapting it
- Assuming parameter names and defaults carry over from another provider
- Pinning to a floating model alias in production instead of a dated version
Continue your research
Use these connected ModelRefs sections to compare alternatives, inspect implementation paths, and review the evidence and governance boundaries relevant to Anthropic API — AI Glossary.
Frequently asked questions
What is Anthropic API?
Anthropic's cloud API providing access to Claude models with the Messages API, tool use, vision, and streaming.
What concepts are related to Anthropic API?
Closely related concepts include openai api, claude, anthropic sdk.