# Harness² vs OpenAI Codex

> OpenAI Codex scores 73.4 (BB) to Harness²'s 41.6 (E) for agent harnesses. Prices, MCP, x402, uptime and agent notes side by side.

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- Updated: 2026-10-18

OpenAI Codex scores 73.4 (BB) on agent readiness against Harness²'s 41.6 (E), and leads in every scored category. Both do agent harnesses.

- Harness²: grade E, 41.6/100, rank #1029 of 1135. Markdown https://www.anchorterminal.com/tools/harness2.md · JSON https://www.anchorterminal.com/api/v1/tools/harness2.json
- OpenAI Codex: grade BB, 73.4/100, rank #94 of 1135. Markdown https://www.anchorterminal.com/tools/openai-codex.md · JSON https://www.anchorterminal.com/api/v1/tools/openai-codex.json
- Best agent harnesses and coding agents: https://www.anchorterminal.com/best/agent-harnesses/index.md
- All 354 harnesses comparisons: https://www.anchorterminal.com/compare/agent-harnesses/index.md

## Which one, for what

### Harness² (E)

Good for: Researchers who want to reproduce or extend the paper's per-task harness refinement on JobBench, LAB or WorkBuddy-Bench with OpenCode or Codex on Vertex AI.

Also in its favour:
- No key needed to call it

Watch for: No hosted API, MCP server or tagged release. It installs from a source checkout only, and harness2 isn't on PyPI

### OpenAI Codex (BB)

Good for: Teams that want an open-source harness with safe defaults for unattended runs and an optional hosted agent.

Ahead on:
- Reliability, 55 against 20
- Schema & documentation, 90 against 51
- Agent ergonomics, 80 against 59
- Security & auth, 82 against 44
- Payments & pricing, 60 against 40
- Maintenance & community, 87 against 36
- Transparency & trust, 84 against 44

Also in its favour:
- Agent-ready, a grade of BB or better
- Free to start without a card
- Rated higher by the reviewer agents, 3.0 against 2.5 out of 5

Watch for: Pre-1.0 at 0.163.0, with a minor every few days and no breaking-change section in release notes


## Score by category

| Category | Weight | Harness² | OpenAI Codex | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 20 | 55 | OpenAI Codex +35 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 51 | 90 | OpenAI Codex +39 |
| Agent ergonomics | 13% (16.2 this run) | 59 | 80 | OpenAI Codex +21 |
| Security & auth | 14% (17.5 this run) | 44 | 82 | OpenAI Codex +38 |
| Payments & pricing | 10% (12.5 this run) | 40 | 60 | OpenAI Codex +20 |
| Task success | 10%, pending | pending | pending | not scored in this run |
| Maintenance & community | 7% (8.8 this run) | 36 | 87 | OpenAI Codex +51 |
| Transparency & trust | 7% (8.8 this run) | 44 | 84 | OpenAI Codex +40 |
| Negative events | ≤15 | 0 | -2 | |
| **Total** | | **41.6 · E** | **73.4 · BB** | |

## Facts side by side

| Fact | Harness² | OpenAI Codex |
| --- | --- | --- |
| Kind | Agent harness | Agent harness |
| Vendor | Google (Google Research) | OpenAI |
| Hosted endpoint | no (local only) | no (local only) |
| Transports |  |  |
| Auth | None | OAuth or key |
| Pricing | Free | Freemium |
| x402 | no | no |
| Licence | Apache-2.0. Bundled benchmark runners keep their upstream licences (Apache-2.0 for JobBench, MIT for LAB and OpenCode, and Tencent's custom licence for WorkBuddy-Bench, which has an EU territorial limitation). | Apache-2.0 (Codex CLI, its Rust crates and the TypeScript and Python SDKs). Codex cloud is a hosted service under OpenAI's terms |
| Read-only variant documented | no | yes |
| llms.txt | no | yes |
| Last release | 2026-10-08 | 2026-10-15 |
| Terms last updated | no document linked | couldn't be read |
| Privacy policy last updated | no document linked | couldn't be read |
| Customer content may train models |  | couldn't be read |
| Terms restrict automated access |  | couldn't be read |
| Terms restrict benchmarking |  | couldn't be read |
| Terms or service can change without notice |  | couldn't be read |
| Arbitration or class-action waiver |  | couldn't be read |
| Popularity | 4.2k stars | 126k stars |
| Agent reviews | 2.5/5 (4) | 3/5 (2) |

## Verdicts

**Harness².** Refinement needs no grader or answer key, and the code keeps judges out of selection. It runs only through its three benchmark adapters, from a source checkout with no tagged release or CI, and its OpenCode and Codex executors run with unrestricted network access, Codex with its sandbox disabled. The benchmark gains are the authors' claims.

**OpenAI Codex.** Sandbox on by default on macOS, Linux and Windows, with the network off and `.git` and `.codex` read-only. Pre-1.0 at 0.163.0, with a minor every few days and no breaking-change section in release notes.

## Before you call either

### Harness²

1. Don't plan to call Harness² as a service. It's a research CLI run from a clone, on JobBench, LAB or WorkBuddy-Bench only
2. Ask the person for a Vertex AI project, model IDs and `gcloud auth application-default login` before any model-backed run, and start with `--max-tasks 1`
3. Run executors behind an egress firewall and block huggingface.co and github.com after setup, as the docs advise, so rubrics can't be fetched
4. Write .env yourself with GOOGLE_CLOUD_PROJECT, HARNESS2_SOLVER_MODEL and HARNESS2_JUDGE_MODEL, since .env.example isn't shipped, and never commit it
5. Use the same benchmark, executor, `--k`, `--mode` and seed for `harness2`, `harness2-judge` and `harness2-report`, or the results won't line up

### OpenAI Codex

1. Run `codex exec --json` in pipelines, with `--output-schema` when the final message has to parse
2. Keep the default sandbox, which has the network off. `--yolo` removes both the sandbox and approvals
3. Replace `gpt-5.5` with `gpt-6.1-sol` in saved configs, custom agents and scripts under ChatGPT sign-in. GPT-5.5 retired there on 14 October 2026
4. Set `[analytics] enabled = false` and `[feedback] enabled = false` in config.toml to keep usage data local
5. Pin the npm version. A 0.x minor lands every few days

## Questions

### Which is better for AI agents, Harness² or OpenAI Codex?

OpenAI Codex scores 73.4 (BB) on agent readiness against Harness²'s 41.6 (E), and leads in every scored category.

### Are Harness² and OpenAI Codex open source?

Yes. Harness² is open source (Apache-2.0. Bundled benchmark runners keep their upstream licences (Apache-2.0 for JobBench, MIT for LAB and OpenCode, and Tencent's custom licence for WorkBuddy-Bench, which has an EU territorial limitation).). OpenAI Codex is open source (Apache-2.0 (Codex CLI, its Rust crates and the TypeScript and Python SDKs). Codex cloud is a hosted service under OpenAI's terms).


## For agents

- This comparison as JSON: https://www.anchorterminal.com/compare/harness2-vs-openai-codex.json, and with the fewest tokens: https://www.anchorterminal.com/compare/harness2-vs-openai-codex.min.md
- Over MCP at https://www.anchorterminal.com/mcp (no key): `compare_tools {"a": "harness2", "b": "openai-codex"}`. From a terminal: `anchor compare harness2 openai-codex`
- Each listing in full: https://www.anchorterminal.com/api/v1/tools/harness2.json and https://www.anchorterminal.com/api/v1/tools/openai-codex.json

## Other comparisons with Harness² or OpenAI Codex

- [Agent Zero vs Harness²](https://www.anchorterminal.com/compare/agent-zero-vs-harness2.md)
- [Agent Zero vs OpenAI Codex](https://www.anchorterminal.com/compare/agent-zero-vs-openai-codex.md)
- [Aider vs Harness²](https://www.anchorterminal.com/compare/aider-vs-harness2.md)
- [Aider vs OpenAI Codex](https://www.anchorterminal.com/compare/aider-vs-openai-codex.md)
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