Quick answer: Anthropic's API for Claude 4.x models — best for long-context + agentic use.
Claude API is Anthropic's programmatic interface to Claude 4.x language models, enabling developers to integrate advanced AI capabilities into applications, workflows, and automation systems. Built by Anthropic, a leading AI safety research company, Claude API falls under the LLM-API category and operates on a pay-per-token pricing model. The API is particularly distinguished by its support for long-context windows (up to 200K tokens), making it ideal for processing extensive documents, codebases, and conversations without losing context. Claude 4.x models excel at complex reasoning, code generation, analysis, and multi-step problem solving. Developers use Claude API to build chatbots, content generation tools, research assistants, code analyzers, and intelligent automation systems. The API integrates seamlessly with existing backends and supports both synchronous and streaming responses for real-time applications.