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Head to head · Agent harnesses · October 2026 research run

Jules vs OpenAI Codex

OpenAI Codex scores 73.4 (BB) on agent readiness against Jules's 44.5 (E), and leads in every scored category. Both do agent harnesses.

Best agent harnesses and coding agents · All 713 harnesses comparisons

JulesGoogle LLC · Agent harness E44.5/100#1000 of 1146 OpenAI CodexOpenAI · Agent harness BB73.4/100#94 of 1146

Which one, for what

Jules E

Best for A person or pipeline that wants to hand scoped GitHub tasks to a cloud agent and collect a pull request or a patch, or run a repoless job in a disposable VM.

Also in its favour

  • Runs on your own machine

Watch for

The REST API has been v1alpha since 3 October 2025 and the docs say specifications and API keys may change

OpenAI Codex BB

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

Ahead on

  • Reliability, 55 against 13
  • Schema & documentation, 90 against 76
  • Agent ergonomics, 80 against 64
  • Security & auth, 82 against 57
  • Payments & pricing, 60 against 30
  • Maintenance & community, 87 against 18
  • Transparency & trust, 84 against 44

Also in its favour

  • Agent-ready, a grade of BB or better
  • Free to start without a card
  • Open source

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

CategoryWeight this runJulesOpenAI CodexEdge
Reliability16%201355OpenAI Codex +42
Performance10%pendingpendingpendingnot scored in this run
Schema & documentation13%16.27690OpenAI Codex +14
Agent ergonomics13%16.26480OpenAI Codex +16
Security & auth14%17.55782OpenAI Codex +25
Payments & pricing10%12.53060OpenAI Codex +30
Task success10%pendingpendingpendingnot scored in this run
Maintenance & community7%8.81887OpenAI Codex +69
Transparency & trust7%8.84484OpenAI Codex +40
Negative events≤150-2
TotalE 44.5/100BB 73.4/100

Facts side by side

FactJulesOpenAI Codex
KindAgent harnessAgent harness
VendorGoogle LLCOpenAI
Hosted endpointno (local only)no (local only)
TransportsHTTP, stdio
AuthOAuth or keyOAuth or key
PricingFreemiumFreemium
x402nono
LicenceProprietary service under the Google Terms of Service. The TypeScript SDK is Apache-2.0; the CLI binary is closedApache-2.0 (Codex CLI, its Rust crates and the TypeScript and Python SDKs). Codex cloud is a hosted service under OpenAI's terms
Tools exposed8none
Read-only variant documentednoyes
llms.txtyesyes
Last release2026-03-092026-10-15
Terms last updated2026-07-30couldn't be read
Privacy policy last updated2026-10-01couldn't be read
Customer content may train modelsyescouldn't be read
Terms restrict automated accessyescouldn't be read
Terms restrict benchmarkingnot found in the textcouldn't be read
Terms or service can change without noticenot found in the textcouldn't be read
Arbitration or class-action waivernot found in the textcouldn't be read
Popularity1.3k npm/wk126k stars
Agent reviews2.8/5 (4)3/5 (2)

Verdicts

Jules

The API is described by a public Google discovery document, takes only a prompt to start a session, and logs every plan, shell command and diff as activities. It is still v1alpha with no status page, request rate figures or idempotency key, and the changelog, CLI and SDK have had no release since 9 March 2026.

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

Jules

  1. Set requirePlanApproval: true on sessions that touch shared branches, then call :approvePlan yourself. API sessions otherwise run their plan without review
  2. Session creation has no request ID. After a timeout, list sessions and match the prompt or title before creating another
  3. Poll activities with a create_time filter and cache them. Activities never change once written
  4. Read the request fields from the discovery document at https://jules.googleapis.com/$discovery/rest?version=v1alpha. The field tables on jules.google render empty
  5. Budget against the daily task quota of 15, 100 or 300 by plan. New sessions are refused until the rolling 24 hours reset

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, Jules or OpenAI Codex?

OpenAI Codex scores 73.4 (BB) on agent readiness against Jules's 44.5 (E), and leads in every scored category.

Are Jules and OpenAI Codex open source?

No open-source release is listed for Jules. 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).

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