GitLab · merge requests · auto-merge · Checked October 24, 2026

GitLab: why auto-merge was refused, merged at once, or canceled

Auto-merge asks GitLab to merge a merge request once its merge checks pass. Through the merge API it is auto_merge: true, from GitLab 17.11; before that it was merge_when_pipeline_succeeds: true, which 17.11 deprecated. Since GitLab 17.7 it waits for all the merge checks, not only the pipeline (GitLab's auto-merge docs). GitLab can still answer 405, merge it on the spot, or cancel it later. All of the following was checked on October 24, 2026 in GitLab's source (lib/api/merge_requests.rb, app/services/auto_merge/merge_when_checks_pass_service.rb, app/models/merge_request.rb) and its merge API docs.

What GitLab does with auto_merge

• First, the same checks as any merge: 400 when the group requires the commit SHA, 401 when your account may not merge into the target branch, 409 when the source branch moved. See why the merge was refused.
• It waits for the pipeline, approvals, requested changes, unresolved threads, a draft, conflicts, other merge requests that block this one, external status checks, security policies, locked files and paths, a required Jira issue, a title pattern and a Merge after date.
• It does not wait for a closed merge request, a source branch without commits, or a rebase the merge method needs (need_rebase).
• It does not wait when nothing is left to wait for: the merge request can merge now and its pipeline is not in progress. With Pipelines must succeed, a pipeline is in progress until it is complete; without it, only while it is waiting or running, so a pipeline stopped at a manual job is not waited for.
• When it does not wait, GitLab merges at once if the pipeline allows it: there is no pipeline and none is being created, or the latest one succeeded. The answer is then the merged merge request, with "state":"merged". If the merge request turns out not to be mergeable, the answer is 422 Branch cannot be merged.
• Otherwise the answer is {"message":"405 Method Not Allowed"}, the same as for an ordinary merge that is stopped, with no reason given.

When auto-merge is set, the answer is 200 with "state":"opened" and "merge_when_pipeline_succeeds":true. On a project with merge trains, the request adds the merge request to the train instead, since GitLab 19.1.

The two 405s that surprise

• A rebase is needed. With the fast-forward or semi-linear merge method and without automatic rebase before merge, a merge request behind its target branch needs a rebase. Auto-merge does not wait for one, so while the pipeline runs GitLab answers 405, even if a review is also missing.
• The pipeline failed, and the project does not require a successful pipeline. If nothing else stops the merge request, GitLab will not wait (nothing is left to wait for) and will not merge at once (the pipeline did not succeed): 405. An ordinary merge, without auto_merge, works. With Pipelines must succeed, GitLab sets auto-merge on a failed pipeline and waits, and merges if a retried job succeeds.

When GitLab cancels auto-merge

From GitLab's docs, it cancels auto-merge when new commits are pushed to the source branch, so that they get a review. It also cancels it when commits are added to the target branch and the merge method is fast-forward or semi-linear without automatic rebase before merge. Keeping it set when that rebase is on came in GitLab 19.3, behind a feature flag that is off by default. The merge request's activity shows a note when GitLab cancels or aborts auto-merge.

Cancelling it

• POST /projects/:id/merge_requests/:merge_request_iid/cancel_auto_merge, from GitLab 19.5: 201 with the merge request; 403 Forbidden when you may not cancel it; 409 Can't cancel the automatic merge when it is not set to auto-merge.
• POST …/cancel_merge_when_pipeline_succeeds, the endpoint older versions have, deprecated in 19.5: 401 when you may not cancel it. When it is not set, the answer is still 201 Created, with {"message":"Can't cancel the automatic merge","status":"error","http_status":406}: the 406 is only in the body, so read status.
• The author may cancel it, and so may anyone who may merge it.

What to do

• 405 with a rebase needed: rebase, and set auto-merge again while the new pipeline runs.
• 405 after a failed pipeline: merge it without auto-merge, or retry the failed jobs and set auto-merge while they run.
• Merged at once: nothing was left to wait for. GitLab waits only for the checks the project turns on, such as required approvals or resolved threads.
• Canceled: look at the new commits, then set auto-merge again.
• 409 or "status":"error" on cancel: there was nothing to cancel. It was merged, canceled already, or never set; merge_when_pipeline_succeeds on the merge request is true only while it is set.

GitLab merge requests in IntelliJ IDEA

Merge Request Inbox for GitLab, a plugin by Lesstep for JetBrains IDEs 2024.1 or later, shows a merge request's merge checks before you merge and merges the head commit you had on screen. While the pipeline runs, its Merge dialog offers auto-merge, and sends both auto_merge and merge_when_pipeline_succeeds, so GitLab versions before and after 17.11 understand it. When GitLab merges at once instead, it says the merge request was merged. From version 1.0.15, when GitLab refuses auto-merge (405), it says that auto-merge does not wait for a rebase the merge method needs, and to merge without auto-merge when the pipeline has already ended without succeeding; when GitLab answers but sets nothing, it says so. Before, it gave the message for an ordinary merge, which names a draft, threads, approvals and the pipeline, all of which auto-merge waits for. Reading is free; approving, commenting and merging are Pro (US$1.50 a month, with a 30-day trial).

GITLAB is a trademark of GitLab Inc.; IntelliJ IDEA is a trademark of JetBrains s.r.o. This page is not affiliated with or endorsed by GitLab Inc. or JetBrains.

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