Comparison

Best AI agent harness in 2026

There is no single best AI agent harness. A harness is the loop, tools, memory, permissions, and stop rules around a model. Use Claude Code or Codex when you want a shipping coding product; use the Claude Agent SDK or OpenAI Agents SDK when you want that loop inside your own app; use Pydantic AI, Google ADK, Microsoft Agent Framework, smolagents, or DeepSeek Harness when you want an open-source runtime you can run yourself.

Last verified November 8, 2026. Cells are licence, list price, and platform from official pages. This is not a quality ranking.

Published November 8, 2026Updated November 8, 2026AI Agents Info Editorial

Key takeaways

A harness is not a model. Two products can share a model and behave differently because the workshop around it differs.
The table lists licence, list price, and platform from official pages. It does not rank quality or invent a score.
Coding products, embeddable SDKs, and local open-source runtimes are different jobs. The variant sections below keep those jobs apart.

Last verified November 2026

Which AI agent harness is best in 2026?

There is no single best AI agent harness. A harness is the loop, tools, memory, permissions, and stop rules around a model. Use Claude Code or Codex when you want a shipping coding product. Use the Claude Agent SDK or the OpenAI Agents SDK when you want that loop inside your own app. Use Pydantic AI, Google ADK, Microsoft Agent Framework, smolagents, or DeepSeek Harness when you want an open-source runtime you can run yourself.

The longer definition is What is an AI agent harness? Public board scores stay on the November 2026 harness benchmark. How to test a change without trusting a composite score is How do you evaluate an AI agent harness? The shelf for this table is Best AI agents.

Which AI agent is best for coding in 2026?

Claude Code and Codex are the two finished coding products with public plan pages and editor or terminal clients on this site. A coding harness is a runtime that can read a repository, edit files, run commands, and stop. Both products sit in the coding agents category. The Claude Agent SDK is the same loop as Claude Code, packaged for Python or TypeScript. Pydantic AI’s Coder agent documents file and shell tools on a LocalWorkspace. Microsoft’s overview describes a Harness Agent for long, multi-step work. Those are different delivery shapes. A Terminal-Bench score that names one of them is not a ranking of the others.

List prices for Claude Code and Codex, rechecked in early November 2026, are compared in Claude Code vs Codex pricing. That page is about plan ladders, not about which harness writes better code.

Which open source AI agent harness can you run in 2026?

MIT or Apache 2.0 runtimes in the table include the OpenAI Agents SDK, Pydantic AI, Google ADK, Microsoft Agent Framework, smolagents, DeepSeek Harness, and CrewAI’s framework. Open source here means a public licence on the runtime, not a free hosted product. The Claude Agent SDK’s Python package is MIT; Anthropic still says use of the SDK is under its Commercial Terms unless a component says otherwise. LangChain’s libraries are open source; LangSmith is a platform with seats and traces.

DeepSeek Harness is still in developer preview. Its README says compatibility-breaking changes are expected. Treat it as a plugin runtime you can read, not as a substitute for a shipping IDE agent. The frameworks directory is the listing shelf.

Can you run an AI agent harness locally in 2026?

Yes: Pydantic AI’s LocalWorkspace and DeepSeek Harness run the harness process on your machine, and smolagents separately documents loading a local model with Transformers or Ollama. Local can mean the harness process, the model weights, or both. Pydantic AI’s LocalWorkspace is not a sandbox unless you swap one in. DeepSeek Harness’s documented start command, npx @deepseek-ai/dsh web, opens a web interface on the machine where you run it. smolagents is the row that documents Transformers or Ollama besides hosted APIs.

Google ADK and Microsoft Agent Framework can run on your servers. That is self-hosted, which is not the same as a laptop-only Ollama setup. If privacy of the weights is the requirement, start with smolagents’ local model docs and confirm the model you actually load. The harnesses topic collects the related guides.

How do AI agent harnesses compare on price and licence?

The table lists 11 harnesses with a Best for label, open-source licence, list price, and platform copied from official pages in November 2026 — not a quality ranking.

Sort any column. A blank would mean the official page did not state the fact. Source numbers match the list at the end of the page. Last verified November 8, 2026. The shelf for this table is Best AI agents.

Claude Code
Codex
Claude Agent SDK
OpenAI Agents SDK
Pydantic AI Harness
Google ADK
Microsoft Agent Framework
smolagents
DDeepSeek Harness
LangChain / LangSmith
CrewAI


Claude Agent SDK	Anthropic	Best for embedding Claude Code	Python package on GitHub is MIT; Anthropic says SDK use is under its Commercial Terms unless a component says otherwise	No separate SDK subscription on claude.com/pricing. Model use is billed at Claude API rates. Opus 5.5 $4 / $20 per million tokens; Sonnet 5.5 $2 / $10. Checked 3 Nov 2026.	Python and TypeScript libraries. Other languages can drive the Claude Code CLI.	[6] [2] [7]
Claude Code	Anthropic	Best for a shipping coding agent	Proprietary product	Not on Free ($0). Pro $20/mo, Max $100/mo, Ultra $200/mo, shared with the rest of Claude. Console use is billed at API rates. Prices exclude tax. Checked 7 Nov 2026.	macOS, Linux, and Windows. Terminal, VS Code, JetBrains, web, iOS, Android, GitHub, Slack.	[1] [2]
Codex	OpenAI	Best for coding on ChatGPT plans	Product on ChatGPT plans; OpenAI describes the harness layer as open source	Checked 6 Nov 2026. Free $0, Go $8/mo, Plus $20, Pro from $100 ($100/$200/$500), Business $20/user/mo billed annually ($25 billed monthly). Included on Free and Go with limits. Codex Cloud is not on Free or Go.	ChatGPT, Codex CLI, IDE extension, and web. Cloud tasks can keep running after you close the laptop.	[3] [4] [5]
CrewAI	CrewAI	Best for role-based crews	MIT (open-source framework)	Cloud Basic is free with 50 workflow executions a month. Enterprise is custom. Checked 3 Nov 2026.	Open-source package plus a hosted cloud product.	[22]
DeepSeek Harness	DeepSeek	Best for a local open-source preview	MIT	No product price. The repository is source. Model calls, if any, are billed by the model you connect.	Local developer preview. npx @deepseek-ai/dsh web starts a web interface on the machine where you run it. Newest listed item on 5 Nov 2026 was pre-release v0.2.2-rc.1 (4 Nov 2026).	[18] [19]
Google ADK	Google	Best for multi-language Google Cloud agents	Apache License 2.0 (Python repository)	No price for ADK itself. Gemini or Google Cloud usage is billed separately. Checked 3 Nov 2026.	Python, TypeScript, Go, Java, and Kotlin. Run on your servers or deploy to Google Cloud.	[13] [14]
LangChain / LangSmith	LangChain	Best for a framework plus LangSmith evals	Open-source libraries; LangSmith is a hosted (and optionally self-hosted) platform	LangSmith Developer $0/seat then pay as you go, up to 5,000 base traces/month. Plus $39/seat, up to 10,000 base traces/month. Enterprise custom. 1 LangChain Standard Unit = $1. Checked 8 Nov 2026.	Open-source libraries plus LangSmith cloud, hybrid, or self-hosted on Enterprise.	[20] [21]
Microsoft Agent Framework	Microsoft	Best for long Python or .NET tasks	MIT	No fee for the framework. You pay the model or cloud you connect. Checked 3 Nov 2026.	Python and .NET. Go SDK in public preview (Go 1.26 or later).	[15]
OpenAI Agents SDK	OpenAI	Best for an MIT embeddable loop	MIT (Python openai-agents and TypeScript @openai/agents)	No SDK licence fee. Model calls go through your OpenAI API account at API rates. OpenAI does not list a separate SDK subscription. Checked 3 Nov 2026.	Python and TypeScript. Runs in your application. Sandbox agents use an isolated workspace.	[8] [9]
Pydantic AI Harness	Pydantic	Best for typed Python plus a Coder	MIT	The library has no fee. Pydantic’s pricing page is for Logfire (Personal free with 10 million records/month; Team $49/mo; Growth $249/mo). Checked 3 Nov 2026.	Python. LocalWorkspace runs file and shell tools on your machine. Optional sandboxes: Modal, E2B, Render, Sprites, Daytona, boxd.	[10] [11] [12]
smolagents	Hugging Face	Best for a local model	Apache License 2.0	No smolagents subscription. You pay the model host you connect, if that host charges. Checked 3 Nov 2026.	Python. Models via Hugging Face Inference, OpenAI/Anthropic through LiteLLM, or locally with Transformers or Ollama. Optional Docker, E2B, Modal, or Blaxel sandboxes.	[16] [17]

Which AI agent harness is best for each job?

Claude Code and Codex fit a shipping coding product; the Claude Agent SDK and OpenAI Agents SDK fit an embedded loop; smolagents fits a documented local-model path.

These are job-fit notes from the documented scope, not scores.

Best for a shipping coding agent
Claude Code and Codex are finished products with a terminal, editor, and plan page. They are not libraries you drop into an unrelated app.
Open the matching listing
Best for embedding a coding loop
The Claude Agent SDK packages Claude Code’s loop for Python or TypeScript. The OpenAI Agents SDK is MIT-licensed and runs the loop in your process.
Open the matching listing
Best open-source typed Python harness
Pydantic AI Harness adds a workspace, plan, memory, and a Coder agent on top of a typed loop. The library is MIT licensed. Logfire is a separate paid product.
Open the matching listing
Best for a local model
smolagents documents Transformers and Ollama. DeepSeek Harness starts a web interface on the machine where you run it. Running the harness locally is not the same as running the model locally.
Open the matching listing

How was this AI agent harness comparison checked?

Every cell comes from an official product page, a licence file, or a listing on this site that already cites that official page.

Prices are list prices with the billing unit the vendor printed. Licences are the SPDX or file name on the repository, not a guess. This page does not invent ratings, traffic, or a composite score, and it does not treat benchmark percentages from different tasks as one experiment.

What else do people ask about AI agent harnesses?

These short answers cover cost, Windows, open source, local runtimes, and why this page has no star ratings.

What is an AI agent harness?

An AI agent harness is the software around a language model that lets the model take steps. It holds the tools, the memory, the permissions, the record of what happened, and the rule for when to stop. On this site, an agent is the model plus that harness.

Is there a single best AI agent harness?

No. A shipping coding product, an embeddable SDK, and a local open-source runtime solve different jobs. This page compares licence, list price, and platform from official sources. It does not publish a quality ranking or a composite score.

What is the best AI agent harness for coding?

If you want a finished coding product, Claude Code and Codex are the two with public plan pages and editor or terminal clients on this site. If you want the same kind of loop inside your own app, the Claude Agent SDK, the OpenAI Agents SDK, and Pydantic AI’s Coder agent are the documented options. Scores from different benchmarks are not treated as a ranking here.

What is the best open source AI agent harness?

Several rows are open source: the OpenAI Agents SDK and Microsoft Agent Framework are MIT; Pydantic AI is MIT; Google ADK and smolagents are Apache 2.0; DeepSeek Harness and CrewAI’s framework are MIT. LangChain’s libraries are open source; LangSmith is a separate platform. Licence text is not the same as a hosted product being free.

What is the best local AI agent harness?

Local has two meanings. The harness can run on your machine while the model is still an API. Pydantic AI’s LocalWorkspace and DeepSeek Harness’s local web UI work that way. smolagents separately documents running the model locally with Transformers or Ollama. This page does not claim those local setups match a hosted coding product.

How much does an AI agent harness cost?

It depends on the product. Claude Code is on Anthropic Pro, Max, and Ultra plans, not Free. Codex rides ChatGPT plans, including Free with limits. Open-source SDKs such as the OpenAI Agents SDK, Pydantic AI, Google ADK, Microsoft Agent Framework, and smolagents have no library fee; you still pay the model you call. LangSmith has seat and trace prices. Every figure in the table is a list price from an official page, dated November 2026.

Does an AI agent harness run on Windows?

Claude Code documents macOS, Linux, and Windows. Codex runs in ChatGPT, a CLI, an IDE extension, and the web. Open-source libraries run wherever you can install Python or TypeScript. Windows here is the computer you develop on, not a computer-use desktop agent.

Why are there no star ratings?

This site does not invent ratings, traffic, or composite scores. A cell is published only when an official page, a licence file, or a listing already checked on this site supports it. Public benchmark scores live on the November 2026 harness benchmark report, copied from official leaderboards.

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<p>There is no single best AI agent harness. A harness is the loop, tools, memory, permissions, and stop rules around a model. Use Claude Code or Codex when you want a shipping coding product; use the Claude Agent SDK or OpenAI Agents SDK when you want that loop inside your own app; use Pydantic AI, Google ADK, Microsoft Agent Framework, smolagents, or DeepSeek Harness when you want an open-source runtime you can run yourself.</p>
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