diff --git a/.github/scripts/merge_pr.php b/.github/scripts/merge_pr.php
new file mode 100644
index 000000000000..67d1cdc75992
--- /dev/null
+++ b/.github/scripts/merge_pr.php
@@ -0,0 +1,231 @@
+<?php
+
+class ProcessResult {
+    public $status;
+    public $stdout;
+    public $stderr;
+}
+
+function run_command(string|array $cmd, ?string $failure_message = 'Unexpected error.'): ProcessResult {
+    if (is_array($cmd)) {
+        $cmd = implode(' ', array_map('escapeshellarg', $cmd));
+    }
+    $pipes = null;
+    $result = new ProcessResult();
+    $descriptor_spec = [0 => ['pipe', 'r'], 1 => ['pipe', 'w'], 2 => ['pipe', 'w']];
+    fwrite(STDERR, "> $cmd\n");
+    $process_handle = proc_open($cmd, $descriptor_spec, $pipes);
+
+    $stdin = $pipes[0];
+    $stdout = $pipes[1];
+    $stderr = $pipes[2];
+
+    fclose($stdin);
+
+    stream_set_blocking($stdout, false);
+    stream_set_blocking($stderr, false);
+
+    $stdout_eof = false;
+    $stderr_eof = false;
+
+    do {
+        $read = [$stdout, $stderr];
+        $write = null;
+        $except = null;
+
+        stream_select($read, $write, $except, 1, 0);
+
+        foreach ($read as $stream) {
+            $chunk = fgets($stream);
+            if ($stream === $stdout) {
+                $result->stdout .= $chunk;
+                fwrite(STDOUT, $chunk);
+            } elseif ($stream === $stderr) {
+                $result->stderr .= $chunk;
+                fwrite(STDERR, $chunk);
+            }
+        }
+
+        $stdout_eof = $stdout_eof || feof($stdout);
+        $stderr_eof = $stderr_eof || feof($stderr);
+    } while(!$stdout_eof || !$stderr_eof);
+
+    fclose($stdout);
+    fclose($stderr);
+
+    $result->status = proc_close($process_handle);
+
+    if ($result->status) {
+        fwrite(STDERR, "Status code: {$result->status}\n");
+        if ($failure_message) {
+            throw new RuntimeException($failure_message);
+        }
+    }
+
+    return $result;
+}
+
+function try_run(array $args): bool {
+    $result = run_command($args, failure_message: null);
+    return $result->status === 0;
+}
+
+function run(array $args, ?string $failure_message = null): bool {
+    $result = run_command($args, $failure_message ?? 'Unexpected error.');
+    return $result->status === 0;
+}
+
+function origin_branch_exists(string $branch): bool {
+    return try_run(['git', 'show-ref', '--verify', '--quiet', "refs/remotes/origin/$branch"]);
+}
+
+function find_next_release_branch(string $current): ?string {
+    if ($current === 'master') {
+        return null;
+    }
+
+    if (!preg_match('(^PHP-(?<major>\d+)\.(?<minor>\d+)$)', $current, $matches)) {
+        throw new RuntimeException("Unsupported target branch $current.");
+    }
+
+    $major = $matches['major'];
+    $minor = $matches['minor'];
+
+    $next = "PHP-$major." . ($minor + 1);
+    if (origin_branch_exists($next)) {
+        return $next;
+    }
+
+    $next = 'PHP-' . ($major + 1) . '.0';
+    if (origin_branch_exists($next)) {
+        return $next;
+    }
+
+    return 'master';
+}
+
+function find_release_branches(string $target): array {
+    $branches = [$target];
+    while (null !== $next = find_next_release_branch(end($branches))) {
+        $branches[] = $next;
+    }
+    return $branches;
+}
+
+function merge_pr_into_target(string $pr_sha, string $pr_first_sha, string $target, string $message, string $description): string {
+    $author = trim(run_command(['git', 'log', '-1', '--format=%an <%ae>', $pr_first_sha])->stdout);
+
+    run(['git', 'checkout', '-B', $target, "refs/remotes/origin/$target"]);
+    run(['git', 'merge', '--squash', $pr_sha],
+        failure_message: "Failed to squash PR into $target.");
+    run(['git', 'commit', "--author=$author", '-m', $message, '-m', wrap_commit_message($description)]);
+    $squashed_sha = trim((string) shell_exec('git rev-parse HEAD'));
+
+    return $squashed_sha;
+}
+
+function merge_upwards(array $branches) {
+    for ($i = 1; $i < count($branches); $i++) {
+        $prev = $branches[$i - 1];
+        $current = $branches[$i];
+        run(['git', 'checkout', '-B', $current, "refs/remotes/origin/$current"]);
+        run(['git', 'merge', '--no-ff', '--no-edit', $prev],
+            failure_message: "Failed to merge $prev into $current.");
+    }
+}
+
+enum PushPrBranchResult {
+    case Success;
+    case Rejected;
+    case RemoteRejected;
+}
+
+function push_pr_branch(string $url, string $branch, string $new_commit, string $expected_commit) {
+    $result = run_command(['git', 'push', "--force-with-lease=$branch:$expected_commit", $url, "$new_commit:refs/heads/$branch"], failure_message: null);
+    if ($result->status === 0) {
+        return PushPrBranchResult::Success;
+    } else if (preg_match('(\[rejected\])', $result->stderr)) {
+        return PushPrBranchResult::Rejected;
+    } else {
+        return PushPrBranchResult::RemoteRejected;
+    }
+}
+
+function push_release_branches(array $branches): bool {
+    return try_run(['git', 'push', '--atomic', 'origin', ...$branches]);
+}
+
+function revert_pr_branch(string $url, string $branch, string $new_commit, string $expected_commit) {
+    run_command(['git', 'push', "--force-with-lease=$branch:$expected_commit", $url, "$new_commit:refs/heads/$branch"],
+        failure_message: 'Failed to push release branches. Reverting PR branch also failed.');
+}
+
+function wrap_commit_message(string $message, int $width = 80): string {
+    $lines = explode("\n", $message);
+    $result = [];
+    $code_section = false;
+
+    foreach ($lines as $line) {
+        if (preg_match('(^\s*```)', $line)) {
+            $code_section = !$code_section;
+            $result[] = $line;
+            continue;
+        }
+
+        if ($code_section) {
+            $result[] = $line;
+            continue;
+        }
+
+        if ($line === '' || preg_match('(^\s)', $line)) {
+            $result[] = $line;
+            continue;
+        }
+
+        $result[] = wordwrap($line, $width, "\n", false);
+    }
+
+    return implode("\n", $result);
+}
+
+function main(): int {
+    $target_sha = getenv('TARGET_SHA');
+    $target_ref = getenv('TARGET_REF');
+    $pr_number = getenv('PR_NUMBER');
+    $pr_sha = getenv('PR_SHA');
+    $pr_ref = getenv('PR_REF');
+    $pr_repo_url = getenv('PR_REPO_URL');
+    $pr_title = getenv('PR_TITLE');
+    $pr_description = getenv('PR_DESCRIPTION');
+    $github_output = getenv('GITHUB_OUTPUT');
+
+    try {
+        $release_branches = find_release_branches($target_ref);
+        $pr_first_sha = trim(run_command("git log --reverse --format=%H $target_sha..$pr_sha | head -n1")->stdout);
+
+        $squashed_sha = merge_pr_into_target($pr_sha, $pr_first_sha, $target_ref, "$pr_title (GH-$pr_number)", $pr_description);
+        merge_upwards($release_branches);
+        $push_pr_branch_result = push_pr_branch($pr_repo_url, $pr_ref, $squashed_sha, $pr_sha);
+        if ($push_pr_branch_result === PushPrBranchResult::Rejected) {
+            throw new RuntimeException('PR branch diverged.');
+        } else if ($push_pr_branch_result === PushPrBranchResult::RemoteRejected) {
+            // Contributor likely unchecked the "Allow edits by maintainers"
+            // checkbox. Resume and close PR manually.
+            file_put_contents($github_output, "close_pr=1\n", FILE_APPEND);
+        }
+        if (!push_release_branches($release_branches)) {
+            revert_pr_branch($pr_repo_url, $pr_ref, $pr_sha, $squashed_sha);
+            throw new RuntimeException('Failed to push release branches.');
+        }
+    } catch (Throwable $e) {
+        if ($github_output !== false) {
+            file_put_contents($github_output, "fail_reason<<EOF\n{$e->getMessage()}\nEOF\n", FILE_APPEND);
+        }
+        fwrite(STDERR, "::error::{$e->getMessage()}\n");
+        return 1;
+    }
+
+    return 0;
+}
+
+exit(main());
diff --git a/.github/workflows/merge_pr.yml b/.github/workflows/merge_pr.yml
new file mode 100644
index 000000000000..7ea5ba5e4050
--- /dev/null
+++ b/.github/workflows/merge_pr.yml
@@ -0,0 +1,108 @@
+name: Merge PR
+
+on:
+  pull_request_target:
+    types: [labeled]
+
+permissions:
+  contents: read
+
+concurrency:
+  group: ${{ github.workflow }}
+
+jobs:
+  merge_pr:
+    name: Merge PR
+    if: github.event.label.name == 'Merge'
+    runs-on: ubuntu-latest
+    permissions:
+      contents: write
+      pull-requests: write
+    steps:
+      - name: git checkout
+        uses: actions/checkout@v6
+        with:
+          fetch-depth: 0
+          filter: blob:none
+          ref: ${{ github.event.pull_request.base.ref }}
+          token: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: git config
+        run: |
+          git config user.name "PHP GH Bot"
+          git config user.email "gh-bot@php.net"
+          git config merge.NEWS.name "Keep the NEWS file"
+          git config merge.NEWS.driver "touch %A"
+          git config merge.log true
+
+      - name: Fetch PR head
+        env:
+          PR_NUMBER: ${{ github.event.pull_request.number }}
+        run: |
+          git fetch origin "refs/pull/${PR_NUMBER}/head"
+
+      - name: Merge PR
+        id: merge
+        env:
+          PR_NUMBER: ${{ github.event.pull_request.number }}
+          PR_FIRST_SHA: $(git log --reverse --format=%H ${{ github.event.pull_request.base.sha }}..${{ github.event.pull_request.head.sha }} | head -n1)
+          PR_SHA: ${{ github.event.pull_request.head.sha }}
+          PR_REF: ${{ github.event.pull_request.head.ref }}
+          PR_REPO_URL: ${{ github.event.pull_request.head.repo.clone_url }}
+          PR_TITLE: ${{ github.event.pull_request.title }}
+          PR_DESCRIPTION: ${{ github.event.pull_request.body }}
+          TARGET_SHA: ${{ github.event.pull_request.base.sha }}
+          TARGET_REF: ${{ github.event.pull_request.base.ref }}
+        run: |
+          # Use merge script from master to avoid syncing to lower branches.
+          git show origin/master:.github/scripts/merge_pr.php > "$RUNNER_TEMP/merge_pr.php"
+          php "$RUNNER_TEMP/merge_pr.php"
+
+      - name: Report failure
+        if: failure()
+        uses: actions/github-script@v9
+        env:
+          FAIL_REASON: ${{ steps.merge.outputs.fail_reason }}
+        with:
+          script: |
+            const reason = process.env.FAIL_REASON || 'Unknown error.';
+            const runUrl = `${context.serverUrl}/${context.repo.owner}/${context.repo.repo}/actions/runs/${context.runId}`;
+
+            await github.rest.issues.createComment({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              issue_number: context.issue.number,
+              body: `Merge failed: ${reason}\n\n[View workflow run](${runUrl}).`,
+            });
+
+      - name: Remove Merge label
+        if: ${{ always() }}
+        uses: actions/github-script@v9
+        with:
+          script: |
+            try {
+              await github.rest.issues.removeLabel({
+                owner: context.repo.owner,
+                repo: context.repo.repo,
+                issue_number: context.issue.number,
+                name: 'Merge',
+              });
+            } catch (e) {
+              core.warning(`Could not remove the 'Merge' label: ${e.message}`);
+            }
+
+      - name: Close PR
+        if: ${{ steps.merge.outputs.close_pr == '1' }}
+        uses: actions/github-script@v9
+        with:
+          script: |
+            try {
+              await github.rest.issues.update({
+                owner: context.repo.owner,
+                repo: context.repo.repo,
+                issue_number: context.issue.number,
+                state: 'closed',
+              });
+            } catch (e) {
+              core.warning(`Could not close the PR: ${e.message}`);
+            }
diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index eafedec5eafa..a016a6088f31 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -34,7 +34,7 @@ concurrency:
 jobs:
   GENERATE_MATRIX:
     name: Generate Matrix
-    if: github.repository == 'php/php-src' || github.event_name == 'pull_request' || github.event_name == 'workflow_dispatch'
+    if: (github.repository == 'php/php-src' || github.event_name == 'pull_request' || github.event_name == 'workflow_dispatch') && !contains(github.event.pull_request.labels.*.name, 'Merge')
     runs-on: ubuntu-latest
     outputs:
       all_variations: ${{ steps.set-matrix.outputs.all_variations }}