Best OpenAI Agents SDK Alternatives in 2026

smolagents is Hugging Face's open-source Python library for building AI agents that write code as actions rather than JSON tool calls. Apache 2.0, ~1,000 lines of core code, supports 100-plus LLMs including local models via Ollama and Transformers.

Vercel AI SDK is an open-source TypeScript toolkit for building AI-powered applications and agents. It provides a unified API across 20+ model providers, streaming UI hooks for React and Vue, structured output with Zod, and a full agent abstraction layer.

OpenAI Codex CLI is an open-source terminal agent that reads your codebase, edits files, and runs shell commands with OS-level sandboxing. Released April 2025, rewritten in Rust, free under Apache 2.0.

OpenHands is an open-source autonomous AI coding agent by All Hands AI. It plans, writes, executes, and debugs code inside a sandboxed environment without requiring manual approval at every step. Free to self-host; cloud tier available.

Agno is an open-source Python framework for building multi-agent AI systems, rebranded from Phidata in January 2025. Model-agnostic, Apache 2.0, with built-in memory, knowledge bases, and a production-ready AgentOS runtime for deploying agents as services.

PydanticAI is an open-source Python framework for building production-grade AI agents. Created by Samuel Colvin (creator of Pydantic), it brings FastAPI-style type safety, structured outputs, and dependency injection to agent development. Free, MIT-licensed, 16k+ GitHub stars.

Genkit is Google's open-source AI framework for TypeScript, Go, and Python developers. It provides typed flows, RAG, tool calling, and multi-agent support with a standout local Developer UI for iterating prompts and debugging traces. Free under Apache 2.0.

Mastra is an open-source TypeScript framework for building production AI agents, from the team behind Gatsby. It ships agents, durable workflows, RAG, built-in memory with SOTA LongMemEval scores, and a visual debugging studio.

Stagehand is an MIT-licensed TypeScript SDK from Browserbase that adds natural-language browser control (act, extract, observe) on top of CDP, letting developers build browser agents that survive UI changes without selector maintenance.

AutoGen is Microsoft Research's open-source Python framework for building multi-agent AI applications. It lets developers define autonomous agents that collaborate through message passing, supporting both conversational workflows and complex agentic pipelines. Free, MIT-licensed, self-hostable.