Claude Code vs OpenAI Codex (Oct 2026): Opus 5.5 vs GPT-6.1 Sol, Plans and Limits

Updated 2026-10-26: Rewritten for the current models (Claude Opus 5.5, Sonnet 5.5 and Haiku 5.5; GPT-6.1 Sol and GPT-6 Luna), the current plan prices and limits on both sides, Claude Code Review going GA, Claude Mods, Codex composer predictions, and fast mode vs Ultrafast. Stale GPT-5.5 and Opus 4.7 benchmark tables and May 2026 billing notes have been removed.

Most engineering teams choosing an AI coding agent end up comparing Claude Code and OpenAI Codex. Both are agentic coders that read your repo, run commands, edit across files, open pull requests, and run in the terminal, the IDE, a desktop app or a cloud sandbox. Since our last update, each vendor has shipped a new model generation and changed its plans, so the earlier comparison (GPT-5.5 vs Opus 4.7) is out of date.

This update covers what changed in September and October 2026, which models each tool now uses by default, what the plans cost and how the limits work, how the two code-review products differ, and which tool fits which kind of team. Every number below comes from vendor documentation, changelogs or the 2026 Stack Overflow Developer Survey (one benchmark row cites a secondary summary of OpenAI's figures), and we name the source each time.

Claude Code vs Codex: TL;DR

• Pick Claude Code if you want the most customizable agent harness (hooks, skills, subagents, and now Mods), Opus-class quality by default even on the $20 plan, and a managed multi-agent PR reviewer for Team or Enterprise orgs.
• Pick OpenAI Codex if you run lots of agent sessions and care about cost per task. GPT-6 Luna is very cheap per token, Pro plans have no five-hour limit, and Ultrafast mode on Pro $500 trades credits for speed.
• Use both if your team is senior and your workloads vary. Claude Code now reads AGENTS.md when a repo has no CLAUDE.md, and a one-line @AGENTS.md import covers repos that have both, so one instruction file can serve both agents.

If you care most about…

What changed since the last update

• Claude Opus 5.5 (released September 22, 2026, per Anthropic) became Claude Code's default Opus in version 2.1.280, with a 1M-token context window at $4/$20 per million input/output tokens. The same release changed the default model on Pro and Team Standard from Sonnet to Opus, "matching Max, Team Premium, and Enterprise."
• Claude Sonnet 5.5 (2.1.284) and Claude Haiku 5.5 (2.1.293) are now the default Sonnet and Haiku models. Both have 1M context. Sonnet 5.5 costs $2/$10 per MTok. Haiku 5.5 costs $0.10/$0.50 for prompts up to 100K tokens and $0.50/$2.50 above that.
• Claude Mods arrived in 2.1.287 (October 1): "plugins may now modify deeper behavior."
• Claude Code Review went GA on October 15 for Team and Enterprise, with three review levels and reviews that Anthropic says now take about 6 to 10 minutes, down from about 20 during the preview.
• Opus 5.5 fast mode costs $8/$40 per MTok, and Claude Code 2.1.304 removed the "research preview" label from the /fast dialog on Opus 5.5, though Anthropic's fast-mode docs still describe the feature as a research preview whose pricing and availability may change.
• GPT-6 Sol and GPT-6 Luna rolled out to Codex on September 22, followed by GPT-6.1 Sol on September 29. GPT-6.1 Sol became the default in Codex CLI's bundled catalog (in the 0.159.1 backport and the 0.161.0 release on October 7).
• GPT-5.5 retired from Codex for ChatGPT sign-ins on October 14, 2026 at 19:00 UTC. API-key sessions are not affected.
• GPT-6.1 Terra arrived in Codex on October 26, the day of this update, on Plus, Pro, Business, Enterprise and Edu. OpenAI describes it as "a fast, efficient model for professional work" with strong image understanding and computer use. We have not tested it yet.
• Codex shipped Ultrafast mode for GPT-6.1 Sol (October 8) on Pro $500 and eligible Enterprise and Edu plans, and composer predictions (October 9) in beta for personal Pro plans.

What each tool is in October 2026

Claude Code (Anthropic)

Claude Code is Anthropic's agentic coder. It runs in the terminal, in VS Code, in the desktop app, on the web at claude.ai/code as cloud sessions (on Anthropic-managed infrastructure or self-hosted runners), and in Slack. You can drive a local session from your phone with Remote Control. It is also available through Amazon Bedrock, Google Vertex AI and Microsoft Foundry. The latest release at the time of writing is 2.1.310.

The model lineup is Opus 5.5 (the default on paid plans), Sonnet 5.5 and Haiku 5.5, all with 1M-token context windows. What sets Claude Code apart is how much of its behavior you can change. CLAUDE.md holds project memory (and Claude Code now reads AGENTS.md instead when a repo has no CLAUDE.md). It also has hooks, skills, slash commands, subagents, routines (scheduled cloud runs), first-class MCP support, a headless claude -p mode, and, as of October, Mods.

OpenAI Codex

Codex is OpenAI's agentic coder. It spans the Codex desktop app, an open-source CLI (Apache-2.0), IDE extensions, Codex on the web, iOS, Slack and GitHub. The CLI ships often. The latest at the time of writing is 0.164.0, released October 23. You can install it with npm install -g @openai/codex, brew install --cask codex, or OpenAI's install script.

The recommended models are GPT-6 Astra ("our most capable model"), GPT-6.1 Sol ("near-Astra performance for complex work at a lower cost than Astra") and GPT-6 Luna ("our most efficient model for focused, high-volume tasks"). Codex uses AGENTS.md for project instructions and runs local commands in an OS-level sandbox. Codex Cloud handles async tasks dispatched from the app, the web, Slack or GitHub.

One-line summary: Claude Code is the more extensible harness with Opus as the default. Codex is the more tiered system, where you choose between Astra, Sol and Luna and between Standard, Fast and Ultrafast speed to balance cost and speed.

Models and default behavior

If you have scripts, custom agents or managed configs that still select gpt-5.5, OpenAI's guidance is to switch them to gpt-6.1-sol on Plus, Pro, Business, Enterprise and Edu (when available), or to gpt-6-luna on Free and Go. OpenAI notes that available options and defaults vary by plan, client, workspace settings and rollout. For the model details, see our GPT-6.1 Sol complete guide and Claude Opus 5.5 complete guide.

Benchmarks: what we can and can't say

There is no clean, independent head-to-head between Opus 5.5 and GPT-6.1 Sol on the same benchmark yet. The two vendors highlight different evaluations:

All three rows are vendor-reported, and none of them compares Opus 5.5 with GPT-6.1 Sol directly, which is the default-vs-default matchup that matters inside these tools. Treat them as a sign that both are frontier-class agentic coders, not as a ranking. The more reliable signal is a one-week trial on your own repository, measuring merged PRs, review churn and usage consumed.

Plans, limits and pricing (as of October 2026)

Claude plans that include Claude Code

Anthropic's pricing FAQ says "every plan has usage limits that reset on a rolling five-hour session window," and paid plans also have weekly limits. Fast mode and Code Review are billed separately through usage credits and do not count against plan limits. If you keep hitting the five-hour window, see our guide on how to stretch Claude Code usage limits.

ChatGPT plans that include Codex

OpenAI publishes estimated local messages per five-hour period on Plus and Standard Business: GPT-6.1 Sol 15 to 160, GPT-6 Sol 15 to 150, GPT-6 Astra 5 to 45, and GPT-6 Luna 350 to 3,000. Local messages and cloud chats share one allowance, cloud tasks "may use more of your allowance than local messages," and OpenAI adds that "weekly limits may also apply" to that allowance. OpenAI does not publish a separate table for Pro, Free or Go, so check the usage dashboard on those plans.

Worked example: one heavy agent session

Suppose a session uses 1.5M input tokens and 150K output tokens. To keep the comparison simple, ignore caching, which in practice cuts input cost a lot on both sides.

Claude Code on API pricing (Opus 5.5):

• Standard: 1.5 × $4 = $6.00 input + 0.15 × $20 = $3.00 output = $9.00
• Fast mode: 1.5 × $8 = $12.00 input + 0.15 × $40 = $6.00 output = $18.00 (exactly 2x)
• Sonnet 5.5 for the same session: 1.5 × $2 = $3.00 + 0.15 × $10 = $1.50 = $4.50

Codex on ChatGPT credits (rates per 1M tokens from OpenAI's pricing page):

• GPT-6.1 Sol, Standard: 1.5 × 50 = 75 + 0.15 × 250 = 37.5, for 112.5 credits
• GPT-6.1 Sol, Fast, on purchased credits (2x): 225 credits
• GPT-6.1 Sol, Ultrafast, on purchased credits (6x): 675 credits
• GPT-6 Luna, Standard: 1.5 × 2.5 = 3.75 + 0.15 × 12.5 = 1.875, for 5.625 credits, about 1/20th of Sol

We have not converted credits to dollars because the Codex pricing page lists credit rates, not a credit price we could confirm. The useful takeaway is the ratios. On Codex, routing bounded tasks to Luna cuts cost by roughly 20x compared with Sol. On Claude Code, dropping from Opus 5.5 to Sonnet 5.5 halves the per-token price. Speed tiers cost more: Claude fast mode is exactly 2x the token price; Codex Fast is 2x on purchased credits and 2.5x on included subscription usage; Codex Ultrafast is 6x on purchased credits and 8x on included usage.

Fast mode vs Ultrafast

Two details matter for budgeting. Claude Code fast mode draws from usage credits "even if you have remaining usage on your plan," and turning it on mid-conversation charges the full uncached fast-mode input price for the whole context, so turn it on at the start. Codex Ultrafast on Pro $500 uses included usage first and then credits. Neither speed tier is a good fit for long unattended runs. Both make sense for live debugging where waiting costs more than tokens.

Code review: Claude Code Review vs Codex Code Review

Both vendors now offer an AI reviewer that posts on GitHub pull requests. They differ in who pays and how much control you get.

• Claude Code Review (GA October 15) is for Team and Enterprise organizations. Several agents read the diff and surrounding code in parallel, a verification step filters out false positives, and findings are posted as inline comments ranked by severity, plus a check run. An org Owner sets one review level for the organization (Quick, Standard or Deep, with Standard as the default) and can give individual repositories their own level. It is billed on tokens through usage credits, with no flat per-review price, and has an org-wide monthly spend limit. You can tune it with REVIEW.md and CLAUDE.md, and trigger it with @claude review. It is not available to orgs with Zero Data Retention or the HIPAA configuration. Anthropic is offering eligible Enterprise orgs at least $10,000 in Code Review credits if claimed by January 15, 2027.
• Codex Code Review is GA on GitHub (GitLab merge requests are in preview). It runs automatically on PRs or when someone comments @codex review, and it is part of Plus and above as one of the cloud integrations. GitHub reviews count against Code Review usage, while reviews run locally (/review in the CLI, IDE or app) count against general limits. You can set a different review_model in config.toml.

Rule of thumb: Claude Code Review is an org-level product with admin controls and metered spend. Codex review is easier to get as an individual on a $20 plan. Both have a free local option (/code-review in Claude Code, /review in Codex).

Claude Mods vs Codex composer predictions

These two October features point in different directions.

Claude Mods (Claude Code 2.1.287) let plugins change how the harness itself behaves. Changelog entries since then describe Mods that draw docked panes and images in the terminal and VS Code, register their own tools, raise notifications, and hook events such as tool.check (approve or refuse a tool call), prompt.change and agent.spawn. Anthropic shipped a built-in Mod, "You should know," in which "a side agent watches your back and flags things you or Claude might miss." For teams, the value is policy and workflow that live in code: managed Mods can enforce org settings, gate risky tool calls, or add a review pane.

Codex composer predictions suggest your next prompt. After Codex responds, the desktop app proposes a follow-up in the message box, and you press Tab to accept it as an editable draft. Nothing is sent automatically. It is a beta for users 18 and older on personal ChatGPT Pro plans in supported regions, in local and SSH threads with GPT-6 Astra and GPT-6.1 Sol.

In short, Mods are for teams building a customized agent platform, and predictions are a convenience for individual users. If customizing the harness matters to you, Claude Code is well ahead here. For how Cursor's Composer and Gemini CLI compare, see Cursor Composer vs Claude Code vs Codex vs Gemini CLI.

Cloud sessions and async work

Both tools now treat cloud execution as a core feature:

• Claude Code cloud sessions run on Anthropic-managed infrastructure or self-hosted runners. They support cloud environments with setup scripts, network settings and environment variables, routines on a schedule, a Changes pane and PR status, and admin controls. Since 2.1.310, Enterprise custom roles can grant cloud sessions and Remote Control per role. Fast mode works in cloud sessions with /fast on.
• Codex Cloud runs tasks dispatched from the Codex app, the web, Slack, iOS or GitHub. Business plans get larger cloud VMs. Cloud tasks share the plan's allowance with local messages and can use more of it.
• Codex Goal mode left experimental on May 21, 2026 and is available in the Codex app, IDE extension and CLI. OpenAI says it lets Codex "drive toward a specific objective for hours or even days." It is still actively maintained: Codex CLI 0.163.0 (October 15) changed how interrupted goal continuations count toward the no-activity limit.

The difference used to be that Codex was cloud-first and Claude Code was local-first. That gap has mostly closed. The remaining differences are in governance (Claude's per-role admin controls) and pricing structure (Codex's single shared allowance).

Security and sandboxing

Codex sandboxes local commands by default. It uses Seatbelt on macOS, bubblewrap on Linux and WSL2, and the native Windows sandbox in PowerShell. Sandbox modes are read-only, workspace-write (the default for local work) and danger-full-access. Approval policies are on-request and never, and an "Approve for me" auto-review option sends eligible approval requests to a reviewer agent without widening the sandbox.

Claude Code also has an OS-level sandbox (Seatbelt on macOS, bubblewrap on Linux and WSL2), but it is off by default. You turn it on with /sandbox or "sandbox": {"enabled": true} in settings. When it's on, writes are limited to the working directory and allowed paths, and network traffic goes through a proxy with an allowlist that starts empty. Native Windows runs commands unsandboxed, so use WSL2 there. Without the sandbox, Claude Code relies on per-tool permission prompts, allow/deny rules and hooks.

The bottom line hasn't changed: Codex is stricter by default, and Claude Code can be just as strict once you configure it. For a full rundown, see how to sandbox AI coding agents.

CLAUDE.md and AGENTS.md

This is one of the more practical changes this year. Anthropic's docs now say Claude Code "can also read a repository's AGENTS.md files in place of CLAUDE.md." Codex has always used AGENTS.md. The catch is the "in place of": by default (Claude Code v2.1.277 and later), Claude reads AGENTS.md only when the repo has no CLAUDE.md, .claude/CLAUDE.md or CLAUDE.local.md in the working directory or above it. If any of those exist, Claude reads "your CLAUDE.md files only" and silently skips AGENTS.md.

For teams running both agents, that leaves three workable layouts:

• AGENTS.md only. Both agents read it. Put Claude-specific, path-scoped rules in .claude/rules/, which loads alongside AGENTS.md.
• CLAUDE.md that imports AGENTS.md. Start CLAUDE.md with an @AGENTS.md line and add Claude-only instructions below it. This is the layout Anthropic recommends when a project has both files.
• Change the setting. Set Project instructions to claude-md-and-agents-md in /config so Claude reads both. It is a per-user or managed setting (Claude Code ignores it in project settings files), so it suits individuals more than a shared repo convention.

See AGENTS.md vs CLAUDE.md vs Cursor rules for layout patterns.

Adoption: what the 2026 Stack Overflow survey shows

The 2026 Stack Overflow Developer Survey asked, "Have you used any of the following coding agents or assistants in the past year?" Of the 12,255 respondents who answered (full AI coding agents data):

The survey's AI summary page rounds these to "Claude Code (66%) and GitHub Copilot (59%) are the leaders for coding agents." Respondents could pick more than one tool, so the figures overlap. Usage share also isn't a quality ranking. It does tell hiring managers which tool candidates are most likely to have used already.

Team-fit verdict

A note for engineering leaders

Developer skill still makes the biggest difference. Both agents can now plan, edit across many files, run tests and review PRs. What separates good output from expensive noise is a developer who scopes tasks well, picks the right model and speed tier for the job, writes useful AGENTS.md and hook policies, and reviews agent PRs carefully. When hiring, test for that directly. Our guide to hiring AI-native engineers covers how to assess it.

FAQ

Is Claude Code or OpenAI Codex better in October 2026?

Neither wins outright. Claude Code gives you Opus 5.5 by default on every paid plan and the most customizable harness. Codex gives you a cheaper high-volume tier (GPT-6 Luna), Pro plans without a five-hour limit, and Ultrafast mode. Published benchmarks are vendor-reported and don't compare the two default models directly.

What models do Claude Code and Codex use by default?

Claude Code defaults to Claude Opus 5.5 on Pro, Max, Team and Enterprise (Pro and Team Standard switched from Sonnet in version 2.1.280). GPT-6.1 Sol is the default in Codex CLI's bundled catalog (since 0.161.0) and OpenAI's recommended model on Plus, Pro, Business, Enterprise and Edu when available. Free and Go get GPT-6 Luna in the desktop app.

Is GPT-5.5 still available in Codex?

Not for ChatGPT sign-ins. It retired from Codex on October 14, 2026 at 19:00 UTC. It is still available through the OpenAI API and in Codex sessions authenticated with an API key.

Which one is cheaper?

Both start at $20 a month. For high-volume work, Codex is usually cheaper because GPT-6 Luna costs a small fraction of GPT-6.1 Sol in credits (2.5 vs 50 credits per 1M input tokens). On Claude Code, Sonnet 5.5 costs half as much per token as Opus 5.5 ($2/$10 vs $4/$20 per MTok). Fast and Ultrafast tiers add multipliers on top; see the worked example for the math.

How do the usage limits differ?

Claude plans use a rolling five-hour session window plus weekly limits on paid plans. Codex Plus and Business publish five-hour message estimates per model. OpenAI says "Pro plans currently have no five-hour limit"; it does not publish Pro weekly figures, so check the usage dashboard.

Do I need Team or Enterprise for Claude Code Review?

Yes. The managed Code Review service is for Team and Enterprise organizations on GitHub and is billed through usage credits. On any plan, you can run /code-review locally in a Claude Code session.

Does Claude Code support AGENTS.md now?

Yes, since v2.1.277, when there is no CLAUDE.md. By default Claude Code reads AGENTS.md only if the repo has no CLAUDE.md, .claude/CLAUDE.md or CLAUDE.local.md in the working directory or above it. If you keep a CLAUDE.md, add an @AGENTS.md import to it, or set Project instructions to claude-md-and-agents-md in /config.

Is either tool open source?

The Codex CLI is Apache-2.0 at github.com/openai/codex. Claude Code's CLI is not open source, though its changelog is public and its extension points (plugins, hooks, Mods, MCP) are documented.

Can I use both on the same repo?

Yes, and it's easier than before. Keep AGENTS.md as the shared instruction file. If you need Claude-only instructions, either put path-scoped rules in .claude/rules/ (they load alongside AGENTS.md) or create a CLAUDE.md that starts with @AGENTS.md. Don't add a CLAUDE.md or .claude/CLAUDE.md without that import, or Claude Code stops reading AGENTS.md. Then route each task to whichever agent and tier is most cost-effective for it.

Weighing other agents too? See Muse Code vs Claude Code, Grok Build vs Claude Code vs Codex CLI, and the best MCP servers for Claude Code and Cursor.

Sources

• Claude Code CHANGELOG (Anthropic, GitHub)
• Code Review is now generally available (Anthropic, Oct 15, 2026)
• Claude Code docs: Code Review and Code Review costs and usage
• Claude Code docs: fast mode
• Claude Code docs: sandboxing
• Claude Code docs: memory (CLAUDE.md and AGENTS.md)
• Introducing Claude Opus 5.5 (Anthropic)
• Claude pricing
• Codex changelog (OpenAI)
• Codex pricing (OpenAI) and Codex plan details
• Codex models and GPT-5.5 retirement (OpenAI)
• Codex Fast and Ultrafast modes (OpenAI)
• Codex Code Review (OpenAI)
• Codex sandboxing (OpenAI)
• openai/codex on GitHub
• Stack Overflow Developer Survey 2026: AI and AI coding agents data
• GPT-6.1 Sol benchmarks explained (Vellum, secondary source for OpenAI-reported DeepSWE figures)

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