Best Open-Source AI Agent Frameworks for Building Custom Agents (2026)

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The LAMP Moment for AI Agents Something remarkable happened this week. Three unrelated stories - GSD 2's standalone launch, LangChain's Deep Agents reference architecture, and a wave of tutorials from independent creators - all decomposed AI agents into the exact same four-layer stack: model → runtime → harness → agent. When frameworks, products, and tutorials independently converge on identical architecture, you are not watching a trend. You are watching a stack crystallize.