The best Python agent harnesses in 2026

This roundup compares Python agent harness SDKs — libraries that supply file and shell tools, planning, sub-agents, context management and sandboxes around a model — judging each on model portability, how much can be taken apart, where commands run, approvals, durability, long-run context handling, tracing and commercial support. Pydantic AI Harness is named the overall pick, with LangChain Deep Agents, the Claude Agent SDK, OpenAI Agents SDK, Codex SDK, OpenHands Software Agent SDK, Strands harness and Microsoft Agent Framework Harness each recommended for specific stacks. The piece states its figures were read from each project's own docs and repository on October 30, 2026, with the Pydantic AI Harness and OpenHands Index figures re-read on November 9, 2026.