Agent SDK vs API vs Claude Code

These three are different levels of abstraction over the same model, and the exam wants you to choose by how much control you need versus how much you want to build and maintain. The Messages API is the lowest level: you own the agent loop, tool orchestration, context management, and retries. Maximum control, maximum code you must write and keep working.

The Claude Agent SDK is a harness that provides the agentic loop, tool execution, context handling, and permissioning so you build a custom agent without reinventing the plumbing — the right pick when you need a bespoke, embedded, or headless agent but not a raw protocol. Claude Code is the fully built product: an interactive and headless coding agent with Skills, MCP, subagents, hooks, and permissions already assembled — the right pick when the packaged developer workflow fits and you would rather configure than build.

The decision rule is use the highest-level surface that meets your requirements. Reach for Claude Code when it already does the job; drop to the Agent SDK when you need a custom agent it cannot express; drop to the raw API only when you need control neither higher layer offers. Building on the API what the SDK already provides — or rebuilding Claude Code on the SDK — is the enablement anti-pattern.