diff --git a/openapi/openapiv2.json b/openapi/openapiv2.json
index 61d98c55a..724519f59 100644
--- a/openapi/openapiv2.json
+++ b/openapi/openapiv2.json
@@ -12173,6 +12173,10 @@
         "startDelay": {
           "type": "string",
           "description": "Time to wait before dispatching the first activity task. This delay is not applied to retry attempts."
+        },
+        "includeOutcome": {
+          "type": "boolean",
+          "description": "Include the outcome in a success response if the activity has completed, and\nid_reuse_policy or id_conflict_policy would have caused a failure response otherwise.\nThis is applicable only when the id_reuse_policy is ACTIVITY_ID_REUSE_POLICY_REJECT_DUPLICATE,\nor the activity succeeded and id_reuse_policy is ACTIVITY_ID_REUSE_POLICY_ALLOW_DUPLICATE_FAILED_ONLY,\nor id_conflict_policy is ACTIVITY_ID_CONFLICT_POLICY_USE_EXISTING."
         }
       }
     },
@@ -18955,6 +18959,10 @@
         "link": {
           "$ref": "#/definitions/v1Link",
           "description": "Link to the started activity."
+        },
+        "outcome": {
+          "$ref": "#/definitions/v1ActivityExecutionOutcome",
+          "description": "Only set if the activity is already completed and include_outcome was true in the request."
         }
       }
     },
diff --git a/openapi/openapiv3.yaml b/openapi/openapiv3.yaml
index f7053f93a..08d0b5f89 100644
--- a/openapi/openapiv3.yaml
+++ b/openapi/openapiv3.yaml
@@ -16377,6 +16377,14 @@ components:
           pattern: ^-?(?:0|[1-9][0-9]{0,11})(?:\.[0-9]{1,9})?s$
           type: string
           description: Time to wait before dispatching the first activity task. This delay is not applied to retry attempts.
+        includeOutcome:
+          type: boolean
+          description: |-
+            Include the outcome in a success response if the activity has completed, and
+             id_reuse_policy or id_conflict_policy would have caused a failure response otherwise.
+             This is applicable only when the id_reuse_policy is ACTIVITY_ID_REUSE_POLICY_REJECT_DUPLICATE,
+             or the activity succeeded and id_reuse_policy is ACTIVITY_ID_REUSE_POLICY_ALLOW_DUPLICATE_FAILED_ONLY,
+             or id_conflict_policy is ACTIVITY_ID_CONFLICT_POLICY_USE_EXISTING.
     StartActivityExecutionResponse:
       type: object
       properties:
@@ -16390,6 +16398,10 @@ components:
           allOf:
             - $ref: '#/components/schemas/Link'
           description: Link to the started activity.
+        outcome:
+          allOf:
+            - $ref: '#/components/schemas/ActivityExecutionOutcome'
+          description: Only set if the activity is already completed and include_outcome was true in the request.
     StartBatchOperationRequest:
       type: object
       properties:
diff --git a/temporal/api/workflowservice/v1/request_response.proto b/temporal/api/workflowservice/v1/request_response.proto
index a4098d9b1..b91213dce 100644
--- a/temporal/api/workflowservice/v1/request_response.proto
+++ b/temporal/api/workflowservice/v1/request_response.proto
@@ -3169,6 +3169,13 @@ message StartActivityExecutionRequest {
     temporal.api.common.v1.OnConflictOptions on_conflict_options = 21;
     // Time to wait before dispatching the first activity task. This delay is not applied to retry attempts.
     google.protobuf.Duration start_delay = 22;
+
+    // Include the outcome in a success response if the activity has completed, and
+    // id_reuse_policy or id_conflict_policy would have caused a failure response otherwise.
+    // This is applicable only when the id_reuse_policy is ACTIVITY_ID_REUSE_POLICY_REJECT_DUPLICATE,
+    // or the activity succeeded and id_reuse_policy is ACTIVITY_ID_REUSE_POLICY_ALLOW_DUPLICATE_FAILED_ONLY,
+    // or id_conflict_policy is ACTIVITY_ID_CONFLICT_POLICY_USE_EXISTING.
+    bool include_outcome = 23;
 }
 
 message StartActivityExecutionResponse {
@@ -3178,6 +3185,8 @@ message StartActivityExecutionResponse {
     bool started = 2;
     // Link to the started activity.
     temporal.api.common.v1.Link link = 3;
+    // Only set if the activity is already completed and include_outcome was true in the request.
+    temporal.api.activity.v1.ActivityExecutionOutcome outcome = 4;
 }
 
 message DescribeActivityExecutionRequest {