diff --git a/openapi/openapiv2.json b/openapi/openapiv2.json
index 917fce76c..84c4a0865 100644
--- a/openapi/openapiv2.json
+++ b/openapi/openapiv2.json
@@ -18794,6 +18794,10 @@
           "type": "string",
           "description": "The run id of the workflow that was started - or just signaled, if it was already running."
         },
+        "firstExecutionRunId": {
+          "type": "string",
+          "description": "If the workflow was started as a result of a de-dupe, this field will contain the run id of the first execution in the chain."
+        },
         "started": {
           "type": "boolean",
           "description": "If true, a new workflow was started."
@@ -18982,6 +18986,10 @@
           "type": "string",
           "description": "The run id of the workflow that was started - or used (via WorkflowIdConflictPolicy USE_EXISTING)."
         },
+        "firstExecutionRunId": {
+          "type": "string",
+          "description": "If the workflow was started as a result of a de-dupe, this field will contain the run id of the first execution in the chain."
+        },
         "started": {
           "type": "boolean",
           "description": "If true, a new workflow was started."
diff --git a/openapi/openapiv3.yaml b/openapi/openapiv3.yaml
index 4ada710f0..bb8c80e97 100644
--- a/openapi/openapiv3.yaml
+++ b/openapi/openapiv3.yaml
@@ -16133,6 +16133,9 @@ components:
         runId:
           type: string
           description: The run id of the workflow that was started - or just signaled, if it was already running.
+        firstExecutionRunId:
+          type: string
+          description: If the workflow was started as a result of a de-dupe, this field will contain the run id of the first execution in the chain.
         started:
           type: boolean
           description: If true, a new workflow was started.
@@ -16757,6 +16760,9 @@ components:
         runId:
           type: string
           description: The run id of the workflow that was started - or used (via WorkflowIdConflictPolicy USE_EXISTING).
+        firstExecutionRunId:
+          type: string
+          description: If the workflow was started as a result of a de-dupe, this field will contain the run id of the first execution in the chain.
         started:
           type: boolean
           description: If true, a new workflow was started.
diff --git a/temporal/api/errordetails/v1/message.proto b/temporal/api/errordetails/v1/message.proto
index 2abb60db6..c95d63bc2 100644
--- a/temporal/api/errordetails/v1/message.proto
+++ b/temporal/api/errordetails/v1/message.proto
@@ -27,6 +27,7 @@ message NotFoundFailure {
 message WorkflowExecutionAlreadyStartedFailure {
     string start_request_id = 1;
     string run_id = 2;
+    string first_execution_run_id = 3;
 }
 
 message NamespaceNotActiveFailure {
diff --git a/temporal/api/workflowservice/v1/request_response.proto b/temporal/api/workflowservice/v1/request_response.proto
index f4012c73d..62a9f47f3 100644
--- a/temporal/api/workflowservice/v1/request_response.proto
+++ b/temporal/api/workflowservice/v1/request_response.proto
@@ -212,6 +212,8 @@ message StartWorkflowExecutionRequest {
 message StartWorkflowExecutionResponse {
     // The run id of the workflow that was started - or used (via WorkflowIdConflictPolicy USE_EXISTING).
     string run_id = 1;
+    // If the workflow was started as a result of a de-dupe, this field will contain the run id of the first execution in the chain.
+    string first_execution_run_id = 6;
     // If true, a new workflow was started.
     bool started = 3;
     // Current execution status of the workflow. Typically remains WORKFLOW_EXECUTION_STATUS_RUNNING
@@ -901,6 +903,8 @@ message SignalWithStartWorkflowExecutionRequest {
 message SignalWithStartWorkflowExecutionResponse {
     // The run id of the workflow that was started - or just signaled, if it was already running.
     string run_id = 1;
+    // If the workflow was started as a result of a de-dupe, this field will contain the run id of the first execution in the chain.
+    string first_execution_run_id = 4;
     // If true, a new workflow was started.
     bool started = 2;
     // Link to be associated with the WorkflowExecutionSignaled event.