diff --git a/.claude/commands/dedupe.md b/.claude/commands/dedupe.md
new file mode 100644
index 0000000000..3f48f3a02a
--- /dev/null
+++ b/.claude/commands/dedupe.md
@@ -0,0 +1,43 @@
+---
+allowed-tools: Bash(gh issue view:*), Bash(gh search:*), Bash(gh issue list:*), Bash(gh api:*), Bash(gh issue comment:*)
+description: Find duplicate GitHub issues
+---
+
+# Issue deduplication command
+
+Find up to 3 likely duplicate issues for a given GitHub issue.
+
+To do this, follow these steps precisely:
+
+1. Use an agent to check if the GitHub issue (a) is closed, (b) does not need to be deduped (eg. because it is broad product feedback without a specific solution, or positive feedback), or (c) already has a duplicate detection comment (check for the exact HTML marker `<!-- dedupe-bot:marker -->` in the issue comments - ignore other bot comments). If so, do not proceed.
+2. Use an agent to view a GitHub issue, and ask the agent to return a summary of the issue
+3. Then, launch 5 parallel agents to search GitHub for duplicates of this issue, using diverse keywords and search approaches, using the summary from Step 2. **IMPORTANT**: Always scope searches with `repo:owner/repo` to constrain results to the current repository only.
+4. Next, feed the results from Steps 2 and 3 into another agent, so that it can filter out false positives, that are likely not actually duplicates of the original issue. If there are no duplicates remaining, do not proceed.
+5. Finally, comment back on the issue with a list of up to three duplicate issues (or zero, if there are no likely duplicates)
+
+Notes (be sure to tell this to your agents, too):
+
+- Use `gh` to interact with GitHub, rather than web fetch
+- Do not use other tools, beyond `gh` (eg. don't use other MCP servers, file edit, etc.)
+- Make a todo list first
+- Always scope searches with `repo:owner/repo` to prevent cross-repo false positives
+- For your comment, follow the following format precisely (assuming for this example that you found 3 suspected duplicates):
+
+---
+
+Found 3 possible duplicate issues:
+
+1. <link to issue>
+2. <link to issue>
+3. <link to issue>
+
+This issue will be automatically closed as a duplicate in 3 days.
+
+- If your issue is a duplicate, please close it and 👍 the existing issue instead
+- To prevent auto-closure, add a comment or 👎 this comment
+
+🤖 Generated with [Claude Code](https://claude.ai/code)
+
+<!-- dedupe-bot:marker -->
+
+---
diff --git a/.github/workflows/auto-close-duplicates.yml b/.github/workflows/auto-close-duplicates.yml
new file mode 100644
index 0000000000..886976bf6a
--- /dev/null
+++ b/.github/workflows/auto-close-duplicates.yml
@@ -0,0 +1,29 @@
+name: Auto-close duplicate issues
+on:
+  schedule:
+    - cron: "0 9 * * *"
+  workflow_dispatch:
+
+jobs:
+  auto-close-duplicates:
+    runs-on: ubuntu-latest
+    timeout-minutes: 10
+    concurrency:
+      group: auto-close-duplicates-${{ github.repository }}
+      cancel-in-progress: true
+    permissions:
+      contents: read
+      issues: write
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Setup Bun
+        uses: ./.github/actions/setup-bun
+
+      - name: Auto-close duplicate issues
+        run: bun run scripts/auto-close-duplicates.ts
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          GITHUB_REPOSITORY: ${{ github.repository }}
diff --git a/.github/workflows/claude-dedupe-issues.yml b/.github/workflows/claude-dedupe-issues.yml
new file mode 100644
index 0000000000..3677f61352
--- /dev/null
+++ b/.github/workflows/claude-dedupe-issues.yml
@@ -0,0 +1,34 @@
+name: Claude Issue Dedupe
+on:
+  issues:
+    types: [opened]
+  workflow_dispatch:
+    inputs:
+      issue_number:
+        description: 'Issue number to process for duplicate detection'
+        required: true
+        type: string
+
+jobs:
+  claude-dedupe-issues:
+    runs-on: ubuntu-latest
+    timeout-minutes: 10
+    concurrency:
+      group: claude-dedupe-issues-${{ github.event.issue.number || inputs.issue_number }}
+      cancel-in-progress: true
+    permissions:
+      contents: read
+      issues: write
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Run Claude Code slash command
+        uses: anthropics/claude-code-base-action@beta
+        with:
+          prompt: "/dedupe ${{ github.repository }}/issues/${{ github.event.issue.number || inputs.issue_number }}"
+          anthropic_api_key: ${{ secrets.ANTHROPIC_API_KEY }}
+          claude_args: "--model claude-sonnet-4-5-20250929"
+          claude_env: |
+            GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
diff --git a/scripts/auto-close-duplicates.ts b/scripts/auto-close-duplicates.ts
new file mode 100644
index 0000000000..d0c33575d7
--- /dev/null
+++ b/scripts/auto-close-duplicates.ts
@@ -0,0 +1,347 @@
+#!/usr/bin/env bun
+
+declare global {
+  var process: {
+    env: Record<string, string | undefined>;
+  };
+}
+
+interface GitHubIssue {
+  number: number;
+  title: string;
+  user: { id: number };
+  created_at: string;
+  pull_request?: object;
+}
+
+interface GitHubComment {
+  id: number;
+  body: string;
+  created_at: string;
+  user: { type?: string; id: number };
+}
+
+interface GitHubReaction {
+  user: { id: number };
+  content: string;
+}
+
+async function sleep(ms: number): Promise<void> {
+  return new Promise(resolve => setTimeout(resolve, ms));
+}
+
+async function githubRequest<T>(
+  endpoint: string,
+  token: string,
+  method: string = "GET",
+  body?: any,
+  retryCount: number = 0,
+): Promise<T> {
+  const maxRetries = 3;
+
+  const response = await fetch(`https://api.github.com${endpoint}`, {
+    method,
+    headers: {
+      Authorization: `Bearer ${token}`,
+      Accept: "application/vnd.github+json",
+      "User-Agent": "auto-close-duplicates-script",
+      ...(body && { "Content-Type": "application/json" }),
+    },
+    ...(body && { body: JSON.stringify(body) }),
+  });
+
+  // Check rate limit headers
+  const rateLimitRemaining = response.headers.get("x-ratelimit-remaining");
+  const rateLimitReset = response.headers.get("x-ratelimit-reset");
+
+  if (rateLimitRemaining && parseInt(rateLimitRemaining) < 100) {
+    console.warn(`[WARNING] GitHub API rate limit low: ${rateLimitRemaining} requests remaining`);
+
+    if (parseInt(rateLimitRemaining) < 10) {
+      const resetTime = rateLimitReset ? parseInt(rateLimitReset) * 1000 : Date.now() + 60000;
+      const waitTime = Math.max(0, resetTime - Date.now());
+      console.warn(`[WARNING] Rate limit critically low, waiting ${Math.ceil(waitTime / 1000)}s until reset`);
+      await sleep(waitTime + 1000); // Add 1s buffer
+    }
+  }
+
+  // Handle rate limit errors with retry
+  if (response.status === 429 || response.status === 403) {
+    if (retryCount >= maxRetries) {
+      throw new Error(`GitHub API rate limit exceeded after ${maxRetries} retries`);
+    }
+
+    const retryAfter = response.headers.get("retry-after");
+    const waitTime = retryAfter ? parseInt(retryAfter) * 1000 : Math.min(1000 * Math.pow(2, retryCount), 32000);
+
+    console.warn(
+      `[WARNING] Rate limited (${response.status}), retry ${retryCount + 1}/${maxRetries} after ${waitTime}ms`,
+    );
+    await sleep(waitTime);
+
+    return githubRequest<T>(endpoint, token, method, body, retryCount + 1);
+  }
+
+  if (!response.ok) {
+    throw new Error(`GitHub API request failed: ${response.status} ${response.statusText}`);
+  }
+
+  return response.json();
+}
+
+async function fetchAllComments(
+  owner: string,
+  repo: string,
+  issueNumber: number,
+  token: string,
+): Promise<GitHubComment[]> {
+  const allComments: GitHubComment[] = [];
+  let page = 1;
+  const perPage = 100;
+
+  while (true) {
+    const comments: GitHubComment[] = await githubRequest(
+      `/repos/${owner}/${repo}/issues/${issueNumber}/comments?per_page=${perPage}&page=${page}`,
+      token,
+    );
+
+    if (comments.length === 0) break;
+
+    allComments.push(...comments);
+    page++;
+
+    // Safety limit
+    if (page > 20) break;
+  }
+
+  return allComments;
+}
+
+async function fetchAllReactions(
+  owner: string,
+  repo: string,
+  commentId: number,
+  token: string,
+  authorId?: number,
+): Promise<GitHubReaction[]> {
+  const allReactions: GitHubReaction[] = [];
+  let page = 1;
+  const perPage = 100;
+
+  while (true) {
+    const reactions: GitHubReaction[] = await githubRequest(
+      `/repos/${owner}/${repo}/issues/comments/${commentId}/reactions?per_page=${perPage}&page=${page}`,
+      token,
+    );
+
+    if (reactions.length === 0) break;
+
+    allReactions.push(...reactions);
+
+    // Early exit if we're looking for a specific author and found their -1 reaction
+    if (authorId && reactions.some(r => r.user.id === authorId && r.content === "-1")) {
+      console.log(`[DEBUG] Found author thumbs down reaction, short-circuiting pagination`);
+      break;
+    }
+
+    page++;
+
+    // Safety limit
+    if (page > 20) break;
+  }
+
+  return allReactions;
+}
+
+function escapeRegExp(str: string): string {
+  return str.replace(/[.*+?^${}()|[\]\\]/g, "\\$&");
+}
+
+function extractDuplicateIssueNumber(commentBody: string, owner: string, repo: string): number | null {
+  // Escape owner and repo to prevent ReDoS attacks
+  const escapedOwner = escapeRegExp(owner);
+  const escapedRepo = escapeRegExp(repo);
+
+  // Try to match same-repo GitHub issue URL format first: https://github.com/owner/repo/issues/123
+  const repoUrlPattern = new RegExp(`github\\.com/${escapedOwner}/${escapedRepo}/issues/(\\d+)`);
+  let match = commentBody.match(repoUrlPattern);
+  if (match) {
+    return parseInt(match[1], 10);
+  }
+
+  // Fallback to #123 format (assumes same repo)
+  match = commentBody.match(/#(\d+)/);
+  if (match) {
+    return parseInt(match[1], 10);
+  }
+
+  return null;
+}
+
+async function closeIssueAsDuplicate(
+  owner: string,
+  repo: string,
+  issueNumber: number,
+  duplicateOfNumber: number,
+  token: string,
+): Promise<void> {
+  // Close the issue as duplicate and add the duplicate label
+  await githubRequest(`/repos/${owner}/${repo}/issues/${issueNumber}`, token, "PATCH", {
+    state: "closed",
+    state_reason: "duplicate",
+    labels: ["duplicate"],
+  });
+
+  await githubRequest(`/repos/${owner}/${repo}/issues/${issueNumber}/comments`, token, "POST", {
+    body: `This issue has been automatically closed as a duplicate of #${duplicateOfNumber}.
+
+If this is incorrect, please re-open this issue or create a new one.
+
+🤖 Generated with [Claude Code](https://claude.ai/code)`,
+  });
+}
+
+async function autoCloseDuplicates(): Promise<void> {
+  console.log("[DEBUG] Starting auto-close duplicates script");
+
+  const token = process.env.GITHUB_TOKEN;
+  if (!token) {
+    throw new Error("GITHUB_TOKEN environment variable is required");
+  }
+  console.log("[DEBUG] GitHub token found");
+
+  // Parse GITHUB_REPOSITORY (format: "owner/repo")
+  const repository = process.env.GITHUB_REPOSITORY || "oven-sh/bun";
+  const [owner, repo] = repository.split("/");
+  if (!owner || !repo) {
+    throw new Error(`Invalid GITHUB_REPOSITORY format: ${repository}`);
+  }
+  console.log(`[DEBUG] Repository: ${owner}/${repo}`);
+
+  const threeDaysAgo = new Date();
+  threeDaysAgo.setDate(threeDaysAgo.getDate() - 3);
+  console.log(`[DEBUG] Checking for duplicate comments older than: ${threeDaysAgo.toISOString()}`);
+
+  console.log("[DEBUG] Fetching open issues created more than 3 days ago...");
+  const allIssues: GitHubIssue[] = [];
+  let page = 1;
+  const perPage = 100;
+
+  while (true) {
+    const pageIssues: GitHubIssue[] = await githubRequest(
+      `/repos/${owner}/${repo}/issues?state=open&per_page=${perPage}&page=${page}`,
+      token,
+    );
+
+    if (pageIssues.length === 0) break;
+
+    // Filter for issues created more than 3 days ago and exclude pull requests
+    const oldEnoughIssues = pageIssues.filter(
+      issue => !issue.pull_request && new Date(issue.created_at) <= threeDaysAgo,
+    );
+
+    allIssues.push(...oldEnoughIssues);
+    page++;
+
+    // Safety limit to avoid infinite loops
+    if (page > 20) break;
+  }
+
+  const issues = allIssues;
+  console.log(`[DEBUG] Found ${issues.length} open issues`);
+
+  let processedCount = 0;
+  let candidateCount = 0;
+
+  for (const issue of issues) {
+    processedCount++;
+    console.log(`[DEBUG] Processing issue #${issue.number} (${processedCount}/${issues.length}): ${issue.title}`);
+
+    console.log(`[DEBUG] Fetching comments for issue #${issue.number}...`);
+    const comments = await fetchAllComments(owner, repo, issue.number, token);
+    console.log(`[DEBUG] Issue #${issue.number} has ${comments.length} comments`);
+
+    const dupeComments = comments.filter(
+      comment =>
+        comment.body.includes("Found") &&
+        comment.body.includes("possible duplicate") &&
+        comment.user?.type === "Bot" &&
+        comment.body.includes("<!-- dedupe-bot:marker -->"),
+    );
+    console.log(`[DEBUG] Issue #${issue.number} has ${dupeComments.length} duplicate detection comments`);
+
+    if (dupeComments.length === 0) {
+      console.log(`[DEBUG] Issue #${issue.number} - no duplicate comments found, skipping`);
+      continue;
+    }
+
+    const lastDupeComment = dupeComments[dupeComments.length - 1];
+    const dupeCommentDate = new Date(lastDupeComment.created_at);
+    console.log(
+      `[DEBUG] Issue #${issue.number} - most recent duplicate comment from: ${dupeCommentDate.toISOString()}`,
+    );
+
+    if (dupeCommentDate > threeDaysAgo) {
+      console.log(`[DEBUG] Issue #${issue.number} - duplicate comment is too recent, skipping`);
+      continue;
+    }
+    console.log(
+      `[DEBUG] Issue #${issue.number} - duplicate comment is old enough (${Math.floor(
+        (Date.now() - dupeCommentDate.getTime()) / (1000 * 60 * 60 * 24),
+      )} days)`,
+    );
+
+    // Filter for human comments (not bot comments) after the duplicate comment
+    const commentsAfterDupe = comments.filter(
+      comment => new Date(comment.created_at) > dupeCommentDate && comment.user?.type !== "Bot",
+    );
+    console.log(
+      `[DEBUG] Issue #${issue.number} - ${commentsAfterDupe.length} human comments after duplicate detection`,
+    );
+
+    if (commentsAfterDupe.length > 0) {
+      console.log(`[DEBUG] Issue #${issue.number} - has human activity after duplicate comment, skipping`);
+      continue;
+    }
+
+    console.log(`[DEBUG] Issue #${issue.number} - checking reactions on duplicate comment...`);
+    const reactions = await fetchAllReactions(owner, repo, lastDupeComment.id, token, issue.user.id);
+    console.log(`[DEBUG] Issue #${issue.number} - duplicate comment has ${reactions.length} reactions`);
+
+    const authorThumbsDown = reactions.some(
+      reaction => reaction.user.id === issue.user.id && reaction.content === "-1",
+    );
+    console.log(`[DEBUG] Issue #${issue.number} - author thumbs down reaction: ${authorThumbsDown}`);
+
+    if (authorThumbsDown) {
+      console.log(`[DEBUG] Issue #${issue.number} - author disagreed with duplicate detection, skipping`);
+      continue;
+    }
+
+    const duplicateIssueNumber = extractDuplicateIssueNumber(lastDupeComment.body, owner, repo);
+    if (!duplicateIssueNumber) {
+      console.log(`[DEBUG] Issue #${issue.number} - could not extract duplicate issue number from comment, skipping`);
+      continue;
+    }
+
+    candidateCount++;
+    const issueUrl = `https://github.com/${owner}/${repo}/issues/${issue.number}`;
+
+    try {
+      console.log(`[INFO] Auto-closing issue #${issue.number} as duplicate of #${duplicateIssueNumber}: ${issueUrl}`);
+      await closeIssueAsDuplicate(owner, repo, issue.number, duplicateIssueNumber, token);
+      console.log(`[SUCCESS] Successfully closed issue #${issue.number} as duplicate of #${duplicateIssueNumber}`);
+    } catch (error) {
+      console.error(`[ERROR] Failed to close issue #${issue.number} as duplicate: ${error}`);
+    }
+  }
+
+  console.log(
+    `[DEBUG] Script completed. Processed ${processedCount} issues, found ${candidateCount} candidates for auto-close`,
+  );
+}
+
+autoCloseDuplicates().catch(console.error);
+
+// Make it a module
+export {};