Beyond Agent Frameworks: The Emerging AI Harness Stack
Why LangChain, Strands, Pi, Omnigent and a new generation of agent infrastructure point to a shift in how we build AI systems For the last few years, much of the conversation about building AI applications has revolved around agent frameworks . LangChain became one of the best-known examples. Then came alternatives such as LlamaIndex, AutoGen, Semantic Kernel, CrewAI, Pydantic AI, Mastra, Strands, Google ADK and the OpenAI Agents SDK. The usual comparison looked something like: Which framework has the best tool calling, memory, RAG, multi-agent support and model integrations? That is increasingly the wrong question. By the middle of 2026, a different architecture was becoming visible. The basic model-and-tools loop was no longer the interesting part of an agent system. Pydantic put it particularly clearly when announcing Pydan...