Best Letta Alternatives in 2026

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.

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.

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.

Augment Code is an enterprise AI coding platform with a proprietary Context Engine that indexes 400,000+ files in real time. Built for large engineering teams, it delivers agentic coding, persistent Memories, and GitHub-integrated code review across complex multi-repo environments.

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.

Zed is a GPU-accelerated, open-source code editor built in Rust by the creators of Atom. It pairs 120fps performance with an open AI agent protocol, letting developers bring their own models or agents rather than locking into a single provider.

LlamaIndex is an open-source data framework for building RAG applications over private data, developed by LlamaIndex, Inc. It includes 300+ data connectors, built-in hierarchical chunking, and LlamaParse for enterprise-grade document parsing. Free OSS core; LlamaCloud starts at $50/mo.

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.

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.

OpenAI's official open-source framework for multi-agent workflows. Launched March 2025 as the production successor to Swarm. Provides handoffs, guardrails, tracing, and voice agent support in Python and TypeScript.