diff --git a/.github/workflows/issue-deduplicator.yml b/.github/workflows/issue-deduplicator.yml
new file mode 100644
index 00000000000..6961f739787
--- /dev/null
+++ b/.github/workflows/issue-deduplicator.yml
@@ -0,0 +1,178 @@
+name: Issue Deduplicator
+
+on:
+  issues:
+    types:
+      - opened
+      - labeled
+
+permissions:
+  issues: write
+  models: read
+
+jobs:
+  find-similar:
+    name: Find similar issues
+    concurrency:
+      group: issue-deduplicator-${{ github.event.issue.number }}
+      cancel-in-progress: false
+    if: |
+      github.event.action == 'opened' ||
+      (github.event.action == 'labeled' && github.event.label.name == 'codex-deduplicate')
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Fetch issues and build prompt
+        id: build-prompt
+        env:
+          GH_TOKEN: ${{ github.token }}
+          REPO: ${{ github.repository }}
+          ISSUE_NUMBER: ${{ github.event.issue.number }}
+        run: |
+          set -eo pipefail
+
+          # Fetch open AND closed so the AI can surface already-answered duplicates
+          gh issue list --repo "$REPO" \
+            --json number,title,body,state \
+            --limit 500 \
+            --state all \
+            --search "sort:created-desc" \
+            | jq --arg cur "$ISSUE_NUMBER" '[
+                .[] | select(.number != ($cur | tonumber)) |
+                { number, title, state, body: ((.body // "")[0:800]) }
+              ]' \
+            > existing-issues.json
+
+          gh issue view "$ISSUE_NUMBER" --repo "$REPO" \
+            --json number,title,body \
+            | jq '{ number, title, body: ((.body // "")[0:2000]) }' \
+            > current-issue.json
+
+          echo "issue_count=$(jq 'length' existing-issues.json)"
+
+          # Build prompt file without heredocs (avoids YAML/bash indentation conflict)
+          {
+            printf 'New issue (JSON):\n'
+            cat current-issue.json
+            printf '\n\nExisting issues — open and closed (JSON array):\n'
+            cat existing-issues.json
+            printf '\n\nReturn a JSON object with this exact shape and nothing else:\n'
+            printf '{"issues": ["<number>", ...], "reason": "<one sentence>"}\n'
+            printf '\nList only issue numbers (as strings) that describe the same underlying\n'
+            printf 'problem or request as the new issue. Closed issues are valid matches if\n'
+            printf 'they already answer or resolve it. At most five. Empty array if no\n'
+            printf 'convincing matches exist.\n'
+          } > dedup-prompt.txt
+
+      - name: Run semantic duplicate detection
+        id: ai
+        uses: actions/ai-inference@b81b2afb8390ee6839b494a404766bef6493c7d9 # v1
+        with:
+          model: openai/gpt-4o-mini
+          max-completion-tokens: 200
+          system-prompt: >
+            You are a GitHub issue triage assistant. Identify duplicate issues
+            based on semantic similarity — same underlying problem, error, or
+            feature request — not just shared keywords. Closed issues are valid
+            matches if they already answer or resolve the new one. Respond only
+            with the requested JSON. No markdown, no explanation outside the JSON.
+          prompt-file: dedup-prompt.txt
+
+      - name: Post duplicate comment
+        uses: actions/github-script@3a2844b7e9c422d3c10d287c895573f7108da1b3 # v9
+        env:
+          AI_RESPONSE: ${{ steps.ai.outputs.response }}
+        with:
+          script: |
+            const fs = require('fs');
+            const { owner, repo } = context.repo;
+            const issue = context.payload.issue;
+            const BOT_MARKER = "<!-- opencodex-dedup-bot -->";
+
+            // Always fetch existing bot comment first — needed for both paths
+            const comments = await github.paginate(github.rest.issues.listComments, {
+              owner, repo, issue_number: issue.number, per_page: 100,
+            });
+            const existing = comments.find(
+              c => c.user?.type === 'Bot' && c.body?.includes(BOT_MARKER),
+            );
+
+            const raw = process.env.AI_RESPONSE ?? '';
+            let parsed;
+            try {
+              const cleaned = raw.replace(/^```(?:json)?\s*/m, '').replace(/\s*```\s*$/m, '').trim();
+              parsed = JSON.parse(cleaned);
+            } catch (err) {
+              core.warning(`AI response was not valid JSON: ${raw}`);
+              return;
+            }
+
+            // Build a whitelist of numbers we actually fetched — guards against hallucinations
+            const fetched = JSON.parse(fs.readFileSync('existing-issues.json', 'utf8'));
+            const validNums = new Set(fetched.map(i => String(i.number)));
+
+            if (!Array.isArray(parsed?.issues)) {
+              core.warning(`AI response has unexpected schema (issues is not an array): ${raw}`);
+              return;
+            }
+
+            const currentNum = String(issue.number);
+            const matches = [...new Set(
+              parsed.issues
+                .map(String)
+                .filter(n => n !== currentNum && validNums.has(n))
+            )].slice(0, 5);
+
+            if (matches.length === 0) {
+              if (existing) {
+                await github.rest.issues.deleteComment({
+                  owner, repo, comment_id: existing.id,
+                });
+                core.info(`Removed stale dedup comment on #${issue.number} — no matches on rescan.`);
+              } else {
+                core.info('No similar issues found.');
+              }
+              return;
+            }
+
+            // Annotate closed matches so reporters know they may already have an answer
+            const closedNums = new Set(
+              fetched.filter(i => i.state === 'closed').map(i => String(i.number))
+            );
+            const list = matches
+              .map(n => closedNums.has(n) ? `- #${n} _(closed)_` : `- #${n}`)
+              .join('\n');
+
+            const body = [
+              BOT_MARKER,
+              'Potential duplicates found — please check whether your issue is already covered:',
+              '',
+              list,
+              '',
+              '_Detected automatically via GitHub Models. Closed issues may already contain an answer. Matches may not be exact._',
+            ].join('\n');
+
+            if (existing) {
+              await github.rest.issues.updateComment({
+                owner, repo, comment_id: existing.id, body,
+              });
+              core.info(`Updated dedup comment on #${issue.number}.`);
+            } else {
+              await github.rest.issues.createComment({
+                owner, repo, issue_number: issue.number, body,
+              });
+              core.info(`Posted dedup comment on #${issue.number} with ${matches.length} match(es).`);
+            }
+
+      - name: Remove codex-deduplicate label
+        if: github.event.action == 'labeled' && github.event.label.name == 'codex-deduplicate'
+        env:
+          GH_TOKEN: ${{ github.token }}
+          GH_REPO: ${{ github.repository }}
+        run: |
+          # Only swallow 404 "label not found"; propagate auth/API/runner failures
+          output=$(gh issue edit "${{ github.event.issue.number }}" --remove-label "codex-deduplicate" 2>&1) && exit 0 || {
+            echo "$output" | grep -qi "could not remove label\|label.*not found\|Label.*not exist" && exit 0
+            echo "$output" >&2
+            exit 1
+          }
\ No newline at end of file