Can Claude or ChatGPT review a GitLab merge request? AI review in 2026

More teams now ask an AI to look over a merge request before a person does. In October 2026 there are three first-party ways to do that on GitLab, plus a fourth that works through any assistant connected to GitLab. Here is what each one does, how you start a review, and what it takes to run.

The options at a glance

Option	How a review starts	Where it runs	Status
GitLab Duo Code Review Flow	Assign @GitLabDuo as a reviewer, mention it, or turn on automatic reviews	GitLab, as a CI/CD job on a runner	Generally available since GitLab 18.8
Codex (ChatGPT)	Comment @codex review, or set automatic reviews	Codex cloud	Beta, on all ChatGPT plans
Claude Code for GitLab CI/CD	A pipeline job: run by hand, on merge request events, or from @claude comments through a webhook	Your GitLab runners	Beta, maintained by GitLab
Claude or ChatGPT on the GitLab MCP server	Ask in chat: “review !482”	Your assistant, acting as you through MCP	MCP server generally available since GitLab 19.5

GitLab Duo: the Code Review Flow

GitLab’s own reviewer is the Code Review Flow, part of the GitLab Duo Agent Platform. It reads the diff, scans the repository for related code first, and leaves comments on specific lines plus a review summary. Follow-up reviews pick up its earlier threads.

• Start it: assign @GitLabDuo as a reviewer, type /assign_reviewer @GitLabDuo, mention @GitLabDuo in a comment, or ask in the GitLab Duo chat sidebar.
• Automatic reviews: in Settings › Merge requests, under GitLab Duo Code Review, select Enable automatic reviews by GitLab Duo. A group can turn it on for all its projects.
• Your rules: write review instructions in .gitlab/duo/mr-review-instructions.yaml, with optional file filters for each rule. Custom instructions are a Premium and Ultimate feature.
• What it needs: GitLab Duo and the Agent Platform turned on, with Allow foundational flows and Code Review on for the top-level group; the Developer role or higher; and a runner to pick up the job, either yours with the gitlab--duo tag or one hosted by GitLab.
• What it costs: it is listed for Free, Premium and Ultimate and consumes GitLab Credits when used. On GitLab.com’s Free tier, you buy those credits.

The older, non-agentic GitLab Duo Code Review is still there for customers with the GitLab Duo Enterprise add-on. GitLab runs one or the other, depending on your add-on and group settings.

ChatGPT: Codex code review

OpenAI’s Codex reviews GitLab merge requests in beta, on every ChatGPT plan. It reads the merge request’s diff, follows the guidance in your repository’s AGENTS.md files, and posts review comments that aim to flag serious issues.

1. Connect GitLab in ChatGPT and Codex. A self-managed or Dedicated instance needs a one-time setup by your ChatGPT workspace admin, including a service account with Developer access: Codex can create one, or the admin supplies a personal access token with the api scope.
2. Create a Codex environment for the project with Enable Codex activity from GitLab, which installs the project webhook. On GitLab.com, reviews need this environment, and creating the webhook takes Maintainer or Owner access.
3. Comment @codex review on a merge request, or set automatic reviews: when a merge request opens, on every push, or with the experimental Smart Trigger.

Write your rules in a ## Code Review Rules section of AGENTS.md, at the repository root or next to the code they govern. A comment like @codex fix the P1 issue asks Codex to push a fix to the branch.

Claude: in your pipeline, or in chat

Claude Code for GitLab CI/CD runs Claude in a job on your GitLab runners. You add one job to .gitlab-ci.yml and an ANTHROPIC_API_KEY masked CI/CD variable (or Amazon Bedrock or Google Cloud credentials), then give it a prompt such as “Review this MR”. It follows your CLAUDE.md, and any change it makes arrives as a merge request, so your approval rules still apply. It is in beta and maintained by GitLab. Two things to know:

• @claude comments need wiring. GitLab doesn’t start the job on a comment by itself. You add a webhook for comments and a listener that calls the pipeline trigger API when a comment contains @claude.
• It costs twice: runner minutes for the job, and Claude API tokens for the work.

Claude or ChatGPT on the GitLab MCP server needs no pipeline at all. Connect the assistant to https://gitlab.com/api/v4/mcp and ask “review !482 and list anything risky”. In ChatGPT that takes developer mode, with full MCP apps on Business, Enterprise and Edu, and your top-level group has to allow MCP access. The assistant acts with your account: it reads the diff and can comment, or approve, with your permissions. It is the quickest way to try an AI review, but it only reviews when you ask. Setup is in how to connect Claude or ChatGPT to GitLab.

Does an AI approval count?

Not the way a person’s does, with one exception. GitLab Duo can approve when it finds nothing and request changes when it does, but that is a beta in GitLab 19.5, off by default. Its approval doesn’t count toward required approvals, though with the beta on its change request blocks the merge just as a person’s would. OpenAI says Codex’s review rules don’t replace tests, branch protections or required approvals. With Claude Code, every change still goes through a merge request that your approval rules govern.

The exception is an assistant on the MCP server: it acts with your account, so if you let it approve, the approval is yours. (How approvals work: can you approve your own GitLab merge request?)

Which one to pick

• Your company already has GitLab Duo: the Code Review Flow is built in. Turn on automatic reviews and add review instructions.
• Your team works in ChatGPT: Codex review takes a few steps once GitLab is connected, and it is on every plan during the beta.
• You want control over what runs and where: Claude Code in your GitLab runners, on the Claude API, Bedrock or Google Cloud.
• You want a second opinion now and then: an assistant on the MCP server.

Treat every AI comment as a suggestion. GitLab’s MCP documentation warns about prompt injection and advises using its tools only on GitLab objects you trust.

The human part, on your phone

An AI review still ends with a person approving and merging. MergeBell sends a push when your review is requested, shows every line comment in a phone-sized diff, the AI’s included, and has Approve and Merge in the free tier. It is on Google Play for Android, with iPhone coming soon. See also how to review a GitLab merge request on your phone.