diff --git a/actions/setup/js/close_issue.cjs b/actions/setup/js/close_issue.cjs
index 47ca716ab2..4294858ad0 100644
--- a/actions/setup/js/close_issue.cjs
+++ b/actions/setup/js/close_issue.cjs
@@ -59,14 +59,16 @@ async function addIssueComment(github, owner, repo, issueNumber, message) {
  * @param {string} owner - Repository owner
  * @param {string} repo - Repository name
  * @param {number} issueNumber - Issue number
+ * @param {string} [stateReason] - The reason for closing: "COMPLETED", "NOT_PLANNED", or "DUPLICATE"
  * @returns {Promise<{number: number, html_url: string, title: string}>} Issue details
  */
-async function closeIssue(github, owner, repo, issueNumber) {
+async function closeIssue(github, owner, repo, issueNumber, stateReason) {
   const { data: issue } = await github.rest.issues.update({
     owner,
     repo,
     issue_number: issueNumber,
     state: "closed",
+    state_reason: (stateReason || "COMPLETED").toLowerCase(),
   });
 
   return issue;
@@ -83,12 +85,13 @@ async function main(config = {}) {
   const requiredTitlePrefix = config.required_title_prefix || "";
   const maxCount = config.max || 10;
   const comment = config.comment || "";
+  const configStateReason = config.state_reason || "COMPLETED";
   const { defaultTargetRepo, allowedRepos } = resolveTargetRepoConfig(config);
 
   // Check if we're in staged mode
   const isStaged = process.env.GH_AW_SAFE_OUTPUTS_STAGED === "true";
 
-  core.info(`Close issue configuration: max=${maxCount}`);
+  core.info(`Close issue configuration: max=${maxCount}, state_reason=${configStateReason}`);
   if (requiredLabels.length > 0) {
     core.info(`Required labels: ${requiredLabels.join(", ")}`);
   }
@@ -259,8 +262,10 @@ async function main(config = {}) {
         core.info(`Issue #${issueNumber} was already closed, comment added successfully`);
         closedIssue = issue;
       } else {
-        core.info(`Closing issue #${issueNumber} in ${itemRepo}`);
-        closedIssue = await closeIssue(github, repoParts.owner, repoParts.repo, issueNumber);
+        // Use item-level state_reason if provided, otherwise fall back to config-level default
+        const stateReason = item.state_reason || configStateReason;
+        core.info(`Closing issue #${issueNumber} in ${itemRepo} with state_reason=${stateReason}`);
+        closedIssue = await closeIssue(github, repoParts.owner, repoParts.repo, issueNumber, stateReason);
         core.info(`✓ Issue #${issueNumber} closed successfully: ${closedIssue.html_url}`);
       }
 
diff --git a/actions/setup/js/close_issue.test.cjs b/actions/setup/js/close_issue.test.cjs
index 449e69f030..9e56df8dd2 100644
--- a/actions/setup/js/close_issue.test.cjs
+++ b/actions/setup/js/close_issue.test.cjs
@@ -597,5 +597,110 @@ describe("close_issue", () => {
       expect(updateCalls[0].owner).toBe("github");
       expect(updateCalls[0].repo).toBe("gh-aw");
     });
+
+    it("should use default state_reason 'COMPLETED' when not specified", async () => {
+      const handler = await main({ max: 10 });
+      const updateCalls = [];
+
+      mockGithub.rest.issues.update = async params => {
+        updateCalls.push(params);
+        return {
+          data: {
+            number: params.issue_number,
+            title: "Test Issue",
+            html_url: `https://github.com/${params.owner}/${params.repo}/issues/${params.issue_number}`,
+          },
+        };
+      };
+
+      const result = await handler({ issue_number: 100, body: "Closing" }, {});
+
+      expect(result.success).toBe(true);
+      expect(updateCalls[0].state_reason).toBe("completed");
+    });
+
+    it("should use item-level state_reason 'DUPLICATE' when specified in message", async () => {
+      const handler = await main({ max: 10 });
+      const updateCalls = [];
+
+      mockGithub.rest.issues.update = async params => {
+        updateCalls.push(params);
+        return {
+          data: {
+            number: params.issue_number,
+            title: "Test Issue",
+            html_url: `https://github.com/${params.owner}/${params.repo}/issues/${params.issue_number}`,
+          },
+        };
+      };
+
+      const result = await handler({ issue_number: 100, body: "Duplicate of #50", state_reason: "DUPLICATE" }, {});
+
+      expect(result.success).toBe(true);
+      expect(updateCalls[0].state_reason).toBe("duplicate");
+    });
+
+    it("should use item-level state_reason 'NOT_PLANNED' when specified in message", async () => {
+      const handler = await main({ max: 10 });
+      const updateCalls = [];
+
+      mockGithub.rest.issues.update = async params => {
+        updateCalls.push(params);
+        return {
+          data: {
+            number: params.issue_number,
+            title: "Test Issue",
+            html_url: `https://github.com/${params.owner}/${params.repo}/issues/${params.issue_number}`,
+          },
+        };
+      };
+
+      const result = await handler({ issue_number: 100, body: "Won't fix", state_reason: "NOT_PLANNED" }, {});
+
+      expect(result.success).toBe(true);
+      expect(updateCalls[0].state_reason).toBe("not_planned");
+    });
+
+    it("should use config-level state_reason as default for all closes", async () => {
+      const handler = await main({ max: 10, state_reason: "DUPLICATE" });
+      const updateCalls = [];
+
+      mockGithub.rest.issues.update = async params => {
+        updateCalls.push(params);
+        return {
+          data: {
+            number: params.issue_number,
+            title: "Test Issue",
+            html_url: `https://github.com/${params.owner}/${params.repo}/issues/${params.issue_number}`,
+          },
+        };
+      };
+
+      const result = await handler({ issue_number: 100, body: "Duplicate" }, {});
+
+      expect(result.success).toBe(true);
+      expect(updateCalls[0].state_reason).toBe("duplicate");
+    });
+
+    it("should prefer item-level state_reason over config-level default", async () => {
+      const handler = await main({ max: 10, state_reason: "NOT_PLANNED" });
+      const updateCalls = [];
+
+      mockGithub.rest.issues.update = async params => {
+        updateCalls.push(params);
+        return {
+          data: {
+            number: params.issue_number,
+            title: "Test Issue",
+            html_url: `https://github.com/${params.owner}/${params.repo}/issues/${params.issue_number}`,
+          },
+        };
+      };
+
+      const result = await handler({ issue_number: 100, body: "Duplicate of #50", state_reason: "DUPLICATE" }, {});
+
+      expect(result.success).toBe(true);
+      expect(updateCalls[0].state_reason).toBe("duplicate");
+    });
   });
 });
diff --git a/actions/setup/js/safe_outputs_tools.json b/actions/setup/js/safe_outputs_tools.json
index 576bbd5529..dd122ee365 100644
--- a/actions/setup/js/safe_outputs_tools.json
+++ b/actions/setup/js/safe_outputs_tools.json
@@ -132,6 +132,11 @@
         "issue_number": {
           "type": ["number", "string"],
           "description": "Issue number to close. This is the numeric ID from the GitHub URL (e.g., 901 in github.com/owner/repo/issues/901). If omitted, closes the issue that triggered this workflow (requires an issue event trigger)."
+        },
+        "state_reason": {
+          "type": "string",
+          "enum": ["COMPLETED", "NOT_PLANNED", "DUPLICATE"],
+          "description": "The reason for closing the issue. Use 'COMPLETED' for resolved issues, 'NOT_PLANNED' for issues that won't be addressed, or 'DUPLICATE' for duplicate issues. Defaults to 'COMPLETED'."
         }
       },
       "additionalProperties": false
diff --git a/docs/src/content/docs/reference/safe-outputs.md b/docs/src/content/docs/reference/safe-outputs.md
index b64a921dcd..7e07c301e7 100644
--- a/docs/src/content/docs/reference/safe-outputs.md
+++ b/docs/src/content/docs/reference/safe-outputs.md
@@ -215,11 +215,12 @@ safe-outputs:
     required-title-prefix: "[bot]"    # only close matching prefix
     max: 20                           # max closures (default: 1)
     target-repo: "owner/repo"         # cross-repository
+    state-reason: "duplicate"         # completed (default), not_planned, duplicate
 ```
 
 **Target**: `"triggering"` (requires issue event), `"*"` (any issue), or number (specific issue).
 
-**State Reasons**: `completed`, `not_planned`, `reopened` (default: `completed`).
+**State Reasons**: `completed`, `not_planned`, `duplicate` (default: `completed`). Can also be set per-item in agent output.
 
 ### Comment Creation (`add-comment:`)
 
diff --git a/pkg/workflow/close_entity_helpers.go b/pkg/workflow/close_entity_helpers.go
index a9f2399390..e00d9f7144 100644
--- a/pkg/workflow/close_entity_helpers.go
+++ b/pkg/workflow/close_entity_helpers.go
@@ -69,6 +69,7 @@ type CloseEntityConfig struct {
 	SafeOutputTargetConfig           `yaml:",inline"`
 	SafeOutputFilterConfig           `yaml:",inline"`
 	SafeOutputDiscussionFilterConfig `yaml:",inline"` // Only used for discussions
+	StateReason                      string           `yaml:"state-reason,omitempty"` // Only used for issues
 }
 
 // CloseEntityJobParams holds the parameters needed to build a close entity job
diff --git a/pkg/workflow/compiler_safe_outputs_config.go b/pkg/workflow/compiler_safe_outputs_config.go
index c4861df8b6..09ce85b149 100644
--- a/pkg/workflow/compiler_safe_outputs_config.go
+++ b/pkg/workflow/compiler_safe_outputs_config.go
@@ -197,6 +197,7 @@ var handlerRegistry = map[string]handlerBuilder{
 			AddIfNotEmpty("required_title_prefix", c.RequiredTitlePrefix).
 			AddIfNotEmpty("target-repo", c.TargetRepoSlug).
 			AddStringSlice("allowed_repos", c.AllowedRepos).
+			AddIfNotEmpty("state_reason", c.StateReason).
 			Build()
 	},
 	"close_discussion": func(cfg *SafeOutputsConfig) map[string]any {