Best AI Agent SDKs Compared (2026): LangGraph, CrewAI, OpenAI, Anthropic, and Google ADK

Six agent SDKs compete for production deployments in 2026. LangGraph leads on state control, CrewAI on rapid prototyping, and the vendor SDKs from Anthropic, OpenAI, and Google ship native tool execution. This guide compares architecture, benchmarks, token efficiency, and gateway compatibility so you can pick the right SDK for your stack.