Codex vs Claude Code (2026): Claude Code vs Codex for building a SaaS

Codex vs Claude Code is mostly a choice of defaults and the account you already pay for. Both AI coding agents read your repository, edit files, run your tests, use MCP servers and can work in the cloud. Claude Code vs Codex in one line: Claude Code fits a Claude plan and CLAUDE.md; Codex fits a ChatGPT plan and AGENTS.md.

Every fact below was checked against Anthropic's and OpenAI's own documentation and pricing pages on 18 October 2026. Both tools change every few weeks, so treat the table as a snapshot and the questions near the end as the part that lasts.

Claude Code vs Codex at a glance

What do Codex and Claude Code have in common?

Nearly every capability. Both have a terminal app, editor extensions, a desktop app and a cloud option; both read a project instruction file before they start; both support skills in the same folder-plus-SKILL.md format, MCP servers, a plan mode, an ask-first mode and a no-limits mode.

So "the careful one versus the fast one" is not a useful way to compare them. The differences that matter for a SaaS build are in the details below: which file each reads, what it does before asking you, and what you pay.

Which reads AGENTS.md, Codex or Claude Code?

Codex reads AGENTS.md natively. Claude Code reads CLAUDE.md, and since v2.1.277 it reads AGENTS.md too, but by default only when the repository has no CLAUDE.md.

Codex starts with a global file in ~/.codex, then walks from the repository root down to the folder you started it in, taking at most one file per folder. Files closer to that folder come later in the combined prompt, so their guidance wins. It stops adding files once they reach 32 KiB combined by default (OpenAI's AGENTS.md guide).

Claude Code loads the CLAUDE.md files above your working folder at launch and a subfolder's file once it works on files there. If both CLAUDE.md and AGENTS.md exist, it reads CLAUDE.md only, unless you change Project instructions in /config. Anthropic's way to share one file between tools is a CLAUDE.md that imports it (Claude Code memory docs):

@AGENTS.md

That line is the whole root CLAUDE.md in shipanysaas. Claude Code pulls AGENTS.md in through the import, Codex reads it directly, and you keep one set of rules. The AGENTS.md guide covers the file itself, and CLAUDE.md explained covers the Claude side.

How do approvals and sandboxing differ?

Codex sandboxes commands by default and asks before crossing that line. Claude Code asks or delegates per action through permission modes, and its shell sandbox is opt-in.

Claude Code has six permission modes, cycled with Shift+Tab in the terminal. Manual asks before most edits, shell commands and network access. Plan mode explores and writes a plan without editing. In auto mode, a separate classifier model reviews actions instead of you; as of v2.1.283 it is the starting mode for terminal and VS Code sessions, so switch to Manual if you want to approve each step. Bypass mode skips prompts, and Anthropic reserves it for isolated containers and VMs. The Bash sandbox is off by default; /sandbox turns it on, on macOS, Linux and WSL2 (permission modes).

Codex pairs a sandbox with an approval setting. By default, commands run inside an operating-system sandbox that limits edits to your workspace. Ask for approval pauses before going beyond it. Approve for me keeps the same boundary but sends eligible requests to a reviewer agent. Full access removes the limits on files and network. You pick the mode with /permissions in the CLI or the control under the composer in the app and IDE extension.

The working rule is the same for both. Plan first for anything that touches the database schema, sign-in or billing, and approve those changes yourself. Keep the no-limits mode for a container you can throw away.

How much do Claude Code and Codex cost?

As of October 2026, the usual entry point for both is $20 a month: Claude Pro for Claude Code, ChatGPT Plus for the full Codex. Codex also has a limited version on ChatGPT's Free and Go plans; Claude Code has none on Claude's Free plan.

Claude Code (Claude pricing):

• Pro: $20 a month, or $17 a month billed yearly.
• Max: from $100 a month.
• Team: standard seats include Claude Code, at $25 a seat monthly or $20 billed yearly.
• Enterprise, or an Anthropic Console account billed at API rates.
• Cloud sessions come with Pro, Max and Team, and with some Enterprise seats.

Codex (Codex pricing):

• Free ($0) and Go ($8 a month): GPT-6 Luna in the desktop app, subject to rollout.
• Plus ($20 a month): Codex on the web, in the CLI and IDE extension, on iOS, plus cloud integrations such as automatic code review.
• Pro: from $100 a month, in $100, $200 and $500 tiers.
• Business: $25 a user monthly or $20 billed yearly; Enterprise and Edu through sales.
• An API key works in the CLI, SDK and IDE extension at API rates, without cloud features. Codex Cloud needs a ChatGPT sign-in.

Usage limits differ by plan and change often, so check both pages on the day you decide.

Which models do Claude Code and Codex use?

As of October 2026, Claude Code defaults to Opus 5.5 on Pro, Max, Team, Enterprise and the Anthropic API, and you can switch to Sonnet or Haiku with /model. OpenAI's Codex docs recommend GPT-6.1 Sol for complex coding where your plan has it, and GPT-6 Luna for focused, repeatable tasks; GPT-5.5 left Codex for ChatGPT sign-ins on 14 October 2026.

Model names move faster than anything else in this comparison. Run your own task on both before deciding on the model alone.

Is Codex or Claude Code better for building a SaaS?

Neither is better in general. Pick the one your existing plan covers, then check it against your real work with these questions:

1. Which account do you already pay for? A Claude plan points to Claude Code; a ChatGPT plan points to Codex.
2. Where do you want to watch the work? Both cover the terminal, VS Code, Cursor and a desktop app. In JetBrains, Claude Code's plugin needs its CLI, while Codex runs inside JetBrains' own AI chat.
3. How much do you want to approve? For fewer prompts, try Claude Code's auto mode and Codex's Approve for me on the same task and see which reviews you trust.
4. Should work continue with your laptop closed? Both cloud options do that; Codex Cloud needs a ChatGPT sign-in.
5. What is already in your repository? An AGENTS.md works with Codex as it is, and with Claude Code directly or through a one-line CLAUDE.md. Skills go in .agents/skills for Codex and .claude/skills for Claude Code.
6. How does each do on your real task? Give both the same small job, such as "add a projects table for team accounts, with row-level security and a test that someone outside the team cannot read it". Compare the questions each asks, the diff, and whether it ran your checks before saying it was done.

Why the repository matters more than the agent

Either agent is only as good as what it can learn about your codebase before it starts. Without that, it invents a pattern your project doesn't use, skips a check, or spends an hour on a setup error someone already solved. Three things fix most of it, and both agents use all three:

• A short, specific AGENTS.md. Where things live, which helpers to use, what must never happen. Anthropic's docs note that specific, concise instructions are followed more consistently. The free AGENTS.md generator gives you a first draft.
• Skills for repeated jobs. A skill teaches one task, such as adding a table with its security policies. Both agents read each skill's description up front and load the full SKILL.md only when a task needs it. More in Agent skills explained.
• Checks the agent must run. Typecheck, lint and tests, listed in AGENTS.md as steps to finish before the agent says it is done. For a SaaS, the ones that matter most fail when security breaks, like a database test that signs in as one customer and tries to read another's data.

Claude Code best practices and Building on the kit with a coding agent go further.

How shipanysaas is set up for both

shipanysaas is a SaaS starter kit: a Next.js web app, plus an Expo app for iOS and Android in the All-in plan, on one Supabase backend. It is written so any agent that reads AGENTS.md can work in it. The kit has no AI features of its own; all of this is for the agent you build with.

• One set of rules. A root AGENTS.md and 16 more in apps and packages. Codex reads them directly; Claude Code reads CLAUDE.md, which is the one-line import shown above.
• The same skills in both places. Up to 49 agent skills in All-in (42 in Starter), with identical copies in .agents/skills for Codex and .claude/skills for Claude Code.
• The kit's MCP server, registered for both. .mcp.json for Claude Code and .codex/config.toml for Codex, each subject to the approval or trust step above.
• Checks before "done". The root AGENTS.md requires pnpm typecheck, pnpm lint:fix, pnpm format:fix, an adversarial /reviewer pass, and /rls-review after any database change.
• Written fixes. docs/troubleshooting/agent-known-issues.md holds 17 written fixes in All-in (6 in Starter) for errors already met while running the kit, and agents are told to check it first.

So picking Codex or Claude Code is not a commitment here. Switch whenever you like, or use both. Every file is listed in Coding agents, and pricing shows what each plan includes.

FAQ

Can I use Codex and Claude Code on the same project?

Yes. Keep the rules in AGENTS.md and make CLAUDE.md import it, so both start from the same instructions. Give each agent its own branch so they don't edit the same files at once, and run the same checks on both before you merge.

Does Claude Code read AGENTS.md?

Yes, from v2.1.277, when the repository has no CLAUDE.md or CLAUDE.local.md. If there is one, Claude Code reads that instead, so start it with @AGENTS.md.

Does Codex read CLAUDE.md?

Not by default. Codex looks for AGENTS.override.md and AGENTS.md, plus any extra names you list in project_doc_fallback_filenames in its config. Keeping the shared rules in AGENTS.md avoids the question.

Is Codex free?

Partly. As of October 2026, ChatGPT's Free and Go plans include Codex with GPT-6 Luna in the desktop app, subject to rollout. The CLI, IDE extension, web and cloud integrations are listed from Plus up.