diff --git a/openapi/openapiv2.json b/openapi/openapiv2.json
index 2f21bedcc..71a705c1f 100644
--- a/openapi/openapiv2.json
+++ b/openapi/openapiv2.json
@@ -1462,6 +1462,128 @@
         ]
       }
     },
+    "/api/v1/namespaces/{namespace}/nexus-requests/endpoints/{endpoint}/services/{service}/operations/{operation}": {
+      "post": {
+        "summary": "StartNexusOperation starts a Nexus operation on an endpoint, communicating directly with the\nendpoint using the caller's namespace credentials.\nThe response follows the Nexus RPC spec semantics: synchronous completion, asynchronous start,\nor operation error.\nHandler errors (e.g., NOT_FOUND, BAD_REQUEST) are returned as gRPC errors.",
+        "operationId": "StartNexusOperation2",
+        "responses": {
+          "200": {
+            "description": "A successful response.",
+            "schema": {
+              "$ref": "#/definitions/v1StartNexusOperationResponse"
+            }
+          },
+          "default": {
+            "description": "An unexpected error response.",
+            "schema": {
+              "$ref": "#/definitions/rpcStatus"
+            }
+          }
+        },
+        "parameters": [
+          {
+            "name": "namespace",
+            "description": "The namespace to authenticate to. This may be different from the target namespace of the specified endpoint.",
+            "in": "path",
+            "required": true,
+            "type": "string"
+          },
+          {
+            "name": "endpoint",
+            "description": "Endpoint name, resolved via the Temporal service's endpoint registry.",
+            "in": "path",
+            "required": true,
+            "type": "string"
+          },
+          {
+            "name": "service",
+            "description": "Nexus service name.",
+            "in": "path",
+            "required": true,
+            "type": "string"
+          },
+          {
+            "name": "operation",
+            "description": "Nexus operation name.",
+            "in": "path",
+            "required": true,
+            "type": "string"
+          },
+          {
+            "name": "body",
+            "in": "body",
+            "required": true,
+            "schema": {
+              "$ref": "#/definitions/WorkflowServiceStartNexusOperationBody"
+            }
+          }
+        ],
+        "tags": [
+          "WorkflowService"
+        ]
+      }
+    },
+    "/api/v1/namespaces/{namespace}/nexus-requests/endpoints/{endpoint}/services/{service}/operations/{operation}/cancel": {
+      "post": {
+        "summary": "CancelNexusOperation requests cancellation of a previously started asynchronous Nexus operation.\nCancellation is cooperative: this forwards a cancel request to the handler, but the operation\nwill only transition to canceled if the handler processes it.",
+        "operationId": "CancelNexusOperation2",
+        "responses": {
+          "200": {
+            "description": "A successful response.",
+            "schema": {
+              "$ref": "#/definitions/v1CancelNexusOperationResponse"
+            }
+          },
+          "default": {
+            "description": "An unexpected error response.",
+            "schema": {
+              "$ref": "#/definitions/rpcStatus"
+            }
+          }
+        },
+        "parameters": [
+          {
+            "name": "namespace",
+            "description": "The namespace to authenticate to. This may be different from the target namespace of the specified endpoint.",
+            "in": "path",
+            "required": true,
+            "type": "string"
+          },
+          {
+            "name": "endpoint",
+            "description": "Endpoint name, resolved via the Temporal service's endpoint registry.",
+            "in": "path",
+            "required": true,
+            "type": "string"
+          },
+          {
+            "name": "service",
+            "description": "Nexus service name.",
+            "in": "path",
+            "required": true,
+            "type": "string"
+          },
+          {
+            "name": "operation",
+            "description": "Nexus operation name.",
+            "in": "path",
+            "required": true,
+            "type": "string"
+          },
+          {
+            "name": "body",
+            "in": "body",
+            "required": true,
+            "schema": {
+              "$ref": "#/definitions/WorkflowServiceCancelNexusOperationBody"
+            }
+          }
+        ],
+        "tags": [
+          "WorkflowService"
+        ]
+      }
+    },
     "/api/v1/namespaces/{namespace}/schedule-count": {
       "get": {
         "summary": "CountSchedules is a visibility API to count schedules in a specific namespace.",
@@ -6032,6 +6154,128 @@
         ]
       }
     },
+    "/namespaces/{namespace}/nexus-requests/endpoints/{endpoint}/services/{service}/operations/{operation}": {
+      "post": {
+        "summary": "StartNexusOperation starts a Nexus operation on an endpoint, communicating directly with the\nendpoint using the caller's namespace credentials.\nThe response follows the Nexus RPC spec semantics: synchronous completion, asynchronous start,\nor operation error.\nHandler errors (e.g., NOT_FOUND, BAD_REQUEST) are returned as gRPC errors.",
+        "operationId": "StartNexusOperation",
+        "responses": {
+          "200": {
+            "description": "A successful response.",
+            "schema": {
+              "$ref": "#/definitions/v1StartNexusOperationResponse"
+            }
+          },
+          "default": {
+            "description": "An unexpected error response.",
+            "schema": {
+              "$ref": "#/definitions/rpcStatus"
+            }
+          }
+        },
+        "parameters": [
+          {
+            "name": "namespace",
+            "description": "The namespace to authenticate to. This may be different from the target namespace of the specified endpoint.",
+            "in": "path",
+            "required": true,
+            "type": "string"
+          },
+          {
+            "name": "endpoint",
+            "description": "Endpoint name, resolved via the Temporal service's endpoint registry.",
+            "in": "path",
+            "required": true,
+            "type": "string"
+          },
+          {
+            "name": "service",
+            "description": "Nexus service name.",
+            "in": "path",
+            "required": true,
+            "type": "string"
+          },
+          {
+            "name": "operation",
+            "description": "Nexus operation name.",
+            "in": "path",
+            "required": true,
+            "type": "string"
+          },
+          {
+            "name": "body",
+            "in": "body",
+            "required": true,
+            "schema": {
+              "$ref": "#/definitions/WorkflowServiceStartNexusOperationBody"
+            }
+          }
+        ],
+        "tags": [
+          "WorkflowService"
+        ]
+      }
+    },
+    "/namespaces/{namespace}/nexus-requests/endpoints/{endpoint}/services/{service}/operations/{operation}/cancel": {
+      "post": {
+        "summary": "CancelNexusOperation requests cancellation of a previously started asynchronous Nexus operation.\nCancellation is cooperative: this forwards a cancel request to the handler, but the operation\nwill only transition to canceled if the handler processes it.",
+        "operationId": "CancelNexusOperation",
+        "responses": {
+          "200": {
+            "description": "A successful response.",
+            "schema": {
+              "$ref": "#/definitions/v1CancelNexusOperationResponse"
+            }
+          },
+          "default": {
+            "description": "An unexpected error response.",
+            "schema": {
+              "$ref": "#/definitions/rpcStatus"
+            }
+          }
+        },
+        "parameters": [
+          {
+            "name": "namespace",
+            "description": "The namespace to authenticate to. This may be different from the target namespace of the specified endpoint.",
+            "in": "path",
+            "required": true,
+            "type": "string"
+          },
+          {
+            "name": "endpoint",
+            "description": "Endpoint name, resolved via the Temporal service's endpoint registry.",
+            "in": "path",
+            "required": true,
+            "type": "string"
+          },
+          {
+            "name": "service",
+            "description": "Nexus service name.",
+            "in": "path",
+            "required": true,
+            "type": "string"
+          },
+          {
+            "name": "operation",
+            "description": "Nexus operation name.",
+            "in": "path",
+            "required": true,
+            "type": "string"
+          },
+          {
+            "name": "body",
+            "in": "body",
+            "required": true,
+            "schema": {
+              "$ref": "#/definitions/WorkflowServiceCancelNexusOperationBody"
+            }
+          }
+        ],
+        "tags": [
+          "WorkflowService"
+        ]
+      }
+    },
     "/namespaces/{namespace}/schedule-count": {
       "get": {
         "summary": "CountSchedules is a visibility API to count schedules in a specific namespace.",
@@ -8923,7 +9167,7 @@
           "type": "array",
           "items": {
             "type": "object",
-            "$ref": "#/definitions/v1Link"
+            "$ref": "#/definitions/apiCommonV1Link"
           },
           "description": "Links to be associated with the WorkflowExecutionSignaled event."
         }
@@ -8944,6 +9188,33 @@
       },
       "description": "UpdateWorkflowOptions represents updating workflow execution options after a workflow reset.\nKeep the parameters in sync with temporal.api.workflowservice.v1.UpdateWorkflowExecutionOptionsRequest."
     },
+    "StartNexusOperationResponseAsyncSuccess": {
+      "type": "object",
+      "properties": {
+        "operationToken": {
+          "type": "string"
+        }
+      },
+      "description": "An operation was started asynchronously. The token can be used for cancellation."
+    },
+    "StartNexusOperationResponseOperationFailure": {
+      "type": "object",
+      "properties": {
+        "failure": {
+          "$ref": "#/definitions/v1Failure"
+        }
+      },
+      "description": "The operation completed unsuccessfully.\nThe operation is considered canceled if the failure has a CanceledFailureInfo object attached."
+    },
+    "StartNexusOperationResponseSyncSuccess": {
+      "type": "object",
+      "properties": {
+        "payload": {
+          "$ref": "#/definitions/v1Payload"
+        }
+      },
+      "description": "An operation completed successfully and synchronously."
+    },
     "UpdateTaskQueueConfigRequestRateLimitUpdate": {
       "type": "object",
       "properties": {
@@ -9116,6 +9387,19 @@
       },
       "description": "Activity trigger will be triggered when an activity is about to start."
     },
+    "WorkflowServiceCancelNexusOperationBody": {
+      "type": "object",
+      "properties": {
+        "identity": {
+          "type": "string",
+          "description": "The identity of the client who initiated this request."
+        },
+        "operationToken": {
+          "type": "string",
+          "description": "Operation token from StartNexusOperationResponse.AsyncSuccess."
+        }
+      }
+    },
     "WorkflowServiceCreateScheduleBody": {
       "type": "object",
       "properties": {
@@ -10007,6 +10291,31 @@
         }
       }
     },
+    "WorkflowServiceStartNexusOperationBody": {
+      "type": "object",
+      "properties": {
+        "identity": {
+          "type": "string",
+          "description": "The identity of the client who initiated this request."
+        },
+        "requestId": {
+          "type": "string",
+          "description": "A unique identifier for this request, used as an idempotency key."
+        },
+        "input": {
+          "$ref": "#/definitions/v1Payload",
+          "description": "Serialized input to the operation."
+        },
+        "links": {
+          "type": "array",
+          "items": {
+            "type": "object",
+            "$ref": "#/definitions/apiCommonV1Link"
+          },
+          "description": "Links for associating the caller with the operation."
+        }
+      }
+    },
     "WorkflowServiceStartWorkflowExecutionBody": {
       "type": "object",
       "properties": {
@@ -10524,6 +10833,30 @@
       },
       "description": "Keep the parameters in sync with:\n  - temporal.api.batch.v1.BatchOperationUpdateWorkflowExecutionOptions.\n  - temporal.api.workflow.v1.PostResetOperation.UpdateWorkflowOptions."
     },
+    "apiCommonV1Link": {
+      "type": "object",
+      "properties": {
+        "workflowEvent": {
+          "$ref": "#/definitions/LinkWorkflowEvent"
+        },
+        "batchJob": {
+          "$ref": "#/definitions/LinkBatchJob"
+        }
+      },
+      "description": "Link can be associated with history events. It might contain information about an external entity\nrelated to the history event. For example, workflow A makes a Nexus call that starts workflow B:\nin this case, a history event in workflow A could contain a Link to the workflow started event in\nworkflow B, and vice-versa."
+    },
+    "apiNexusV1Link": {
+      "type": "object",
+      "properties": {
+        "url": {
+          "type": "string",
+          "description": "See https://github.com/nexus-rpc/api/blob/main/SPEC.md#links."
+        },
+        "type": {
+          "type": "string"
+        }
+      }
+    },
     "protobufAny": {
       "type": "object",
       "properties": {
@@ -11525,7 +11858,7 @@
           "type": "array",
           "items": {
             "type": "object",
-            "$ref": "#/definitions/v1Link"
+            "$ref": "#/definitions/apiCommonV1Link"
           },
           "description": "Links associated with the callback. It can be used to link to underlying resources of the\ncallback."
         }
@@ -11600,6 +11933,9 @@
       ],
       "default": "CANCEL_EXTERNAL_WORKFLOW_EXECUTION_FAILED_CAUSE_UNSPECIFIED"
     },
+    "v1CancelNexusOperationResponse": {
+      "type": "object"
+    },
     "v1CanceledFailureInfo": {
       "type": "object",
       "properties": {
@@ -12987,7 +13323,7 @@
           "type": "array",
           "items": {
             "type": "object",
-            "$ref": "#/definitions/v1Link"
+            "$ref": "#/definitions/apiCommonV1Link"
           },
           "description": "Links associated with the event."
         },
@@ -13238,18 +13574,6 @@
       },
       "description": "IntervalSpec matches times that can be expressed as:\nepoch + n * interval + phase\nwhere n is an integer.\nphase defaults to zero if missing. interval is required.\nBoth interval and phase must be non-negative and are truncated to the nearest\nsecond before any calculations.\nFor example, an interval of 1 hour with phase of zero would match every hour,\non the hour. The same interval but a phase of 19 minutes would match every\nxx:19:00. An interval of 28 days with phase zero would match\n2022-02-17T00:00:00Z (among other times). The same interval with a phase of 3\ndays, 5 hours, and 23 minutes would match 2022-02-20T05:23:00Z instead."
     },
-    "v1Link": {
-      "type": "object",
-      "properties": {
-        "workflowEvent": {
-          "$ref": "#/definitions/LinkWorkflowEvent"
-        },
-        "batchJob": {
-          "$ref": "#/definitions/LinkBatchJob"
-        }
-      },
-      "description": "Link can be associated with history events. It might contain information about an external entity\nrelated to the history event. For example, workflow A makes a Nexus call that starts workflow B:\nin this case, a history event in workflow A could contain a Link to the workflow started event in\nworkflow B, and vice-versa."
-    },
     "v1ListActivityExecutionsResponse": {
       "type": "object",
       "properties": {
@@ -15836,6 +16160,28 @@
         }
       }
     },
+    "v1StartNexusOperationResponse": {
+      "type": "object",
+      "properties": {
+        "syncSuccess": {
+          "$ref": "#/definitions/StartNexusOperationResponseSyncSuccess"
+        },
+        "asyncSuccess": {
+          "$ref": "#/definitions/StartNexusOperationResponseAsyncSuccess"
+        },
+        "operationFailure": {
+          "$ref": "#/definitions/StartNexusOperationResponseOperationFailure"
+        },
+        "links": {
+          "type": "array",
+          "items": {
+            "type": "object",
+            "$ref": "#/definitions/apiNexusV1Link"
+          },
+          "description": "Links associated with the operation, as returned by the handler."
+        }
+      }
+    },
     "v1StartWorkflowExecutionResponse": {
       "type": "object",
       "properties": {
@@ -15856,7 +16202,7 @@
           "description": "When `request_eager_execution` is set on the `StartWorkflowExecutionRequest`, the server - if supported - will\nreturn the first workflow task to be eagerly executed.\nThe caller is expected to have a worker available to process the task."
         },
         "link": {
-          "$ref": "#/definitions/v1Link",
+          "$ref": "#/definitions/apiCommonV1Link",
           "description": "Link to the workflow event."
         }
       }
diff --git a/openapi/openapiv3.yaml b/openapi/openapiv3.yaml
index c220f6773..e9d67cf82 100644
--- a/openapi/openapiv3.yaml
+++ b/openapi/openapiv3.yaml
@@ -1343,6 +1343,114 @@ paths:
             application/json:
               schema:
                 $ref: '#/components/schemas/Status'
+  /api/v1/namespaces/{namespace}/nexus-requests/endpoints/{endpoint}/services/{service}/operations/{operation}:
+    post:
+      tags:
+        - WorkflowService
+      description: |-
+        StartNexusOperation starts a Nexus operation on an endpoint, communicating directly with the
+         endpoint using the caller's namespace credentials.
+         The response follows the Nexus RPC spec semantics: synchronous completion, asynchronous start,
+         or operation error.
+         Handler errors (e.g., NOT_FOUND, BAD_REQUEST) are returned as gRPC errors.
+      operationId: StartNexusOperation
+      parameters:
+        - name: namespace
+          in: path
+          description: The namespace to authenticate to. This may be different from the target namespace of the specified endpoint.
+          required: true
+          schema:
+            type: string
+        - name: endpoint
+          in: path
+          description: Endpoint name, resolved via the Temporal service's endpoint registry.
+          required: true
+          schema:
+            type: string
+        - name: service
+          in: path
+          description: Nexus service name.
+          required: true
+          schema:
+            type: string
+        - name: operation
+          in: path
+          description: Nexus operation name.
+          required: true
+          schema:
+            type: string
+      requestBody:
+        content:
+          application/json:
+            schema:
+              $ref: '#/components/schemas/StartNexusOperationRequest'
+        required: true
+      responses:
+        "200":
+          description: OK
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/StartNexusOperationResponse'
+        default:
+          description: Default error response
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/Status'
+  /api/v1/namespaces/{namespace}/nexus-requests/endpoints/{endpoint}/services/{service}/operations/{operation}/cancel:
+    post:
+      tags:
+        - WorkflowService
+      description: |-
+        CancelNexusOperation requests cancellation of a previously started asynchronous Nexus operation.
+         Cancellation is cooperative: this forwards a cancel request to the handler, but the operation
+         will only transition to canceled if the handler processes it.
+      operationId: CancelNexusOperation
+      parameters:
+        - name: namespace
+          in: path
+          description: The namespace to authenticate to. This may be different from the target namespace of the specified endpoint.
+          required: true
+          schema:
+            type: string
+        - name: endpoint
+          in: path
+          description: Endpoint name, resolved via the Temporal service's endpoint registry.
+          required: true
+          schema:
+            type: string
+        - name: service
+          in: path
+          description: Nexus service name.
+          required: true
+          schema:
+            type: string
+        - name: operation
+          in: path
+          description: Nexus operation name.
+          required: true
+          schema:
+            type: string
+      requestBody:
+        content:
+          application/json:
+            schema:
+              $ref: '#/components/schemas/CancelNexusOperationRequest'
+        required: true
+      responses:
+        "200":
+          description: OK
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/CancelNexusOperationResponse'
+        default:
+          description: Default error response
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/Status'
   /api/v1/namespaces/{namespace}/schedule-count:
     get:
       tags:
@@ -5436,6 +5544,114 @@ paths:
             application/json:
               schema:
                 $ref: '#/components/schemas/Status'
+  /namespaces/{namespace}/nexus-requests/endpoints/{endpoint}/services/{service}/operations/{operation}:
+    post:
+      tags:
+        - WorkflowService
+      description: |-
+        StartNexusOperation starts a Nexus operation on an endpoint, communicating directly with the
+         endpoint using the caller's namespace credentials.
+         The response follows the Nexus RPC spec semantics: synchronous completion, asynchronous start,
+         or operation error.
+         Handler errors (e.g., NOT_FOUND, BAD_REQUEST) are returned as gRPC errors.
+      operationId: StartNexusOperation
+      parameters:
+        - name: namespace
+          in: path
+          description: The namespace to authenticate to. This may be different from the target namespace of the specified endpoint.
+          required: true
+          schema:
+            type: string
+        - name: endpoint
+          in: path
+          description: Endpoint name, resolved via the Temporal service's endpoint registry.
+          required: true
+          schema:
+            type: string
+        - name: service
+          in: path
+          description: Nexus service name.
+          required: true
+          schema:
+            type: string
+        - name: operation
+          in: path
+          description: Nexus operation name.
+          required: true
+          schema:
+            type: string
+      requestBody:
+        content:
+          application/json:
+            schema:
+              $ref: '#/components/schemas/StartNexusOperationRequest'
+        required: true
+      responses:
+        "200":
+          description: OK
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/StartNexusOperationResponse'
+        default:
+          description: Default error response
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/Status'
+  /namespaces/{namespace}/nexus-requests/endpoints/{endpoint}/services/{service}/operations/{operation}/cancel:
+    post:
+      tags:
+        - WorkflowService
+      description: |-
+        CancelNexusOperation requests cancellation of a previously started asynchronous Nexus operation.
+         Cancellation is cooperative: this forwards a cancel request to the handler, but the operation
+         will only transition to canceled if the handler processes it.
+      operationId: CancelNexusOperation
+      parameters:
+        - name: namespace
+          in: path
+          description: The namespace to authenticate to. This may be different from the target namespace of the specified endpoint.
+          required: true
+          schema:
+            type: string
+        - name: endpoint
+          in: path
+          description: Endpoint name, resolved via the Temporal service's endpoint registry.
+          required: true
+          schema:
+            type: string
+        - name: service
+          in: path
+          description: Nexus service name.
+          required: true
+          schema:
+            type: string
+        - name: operation
+          in: path
+          description: Nexus operation name.
+          required: true
+          schema:
+            type: string
+      requestBody:
+        content:
+          application/json:
+            schema:
+              $ref: '#/components/schemas/CancelNexusOperationRequest'
+        required: true
+      responses:
+        "200":
+          description: OK
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/CancelNexusOperationResponse'
+        default:
+          description: Default error response
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/Status'
   /namespaces/{namespace}/schedule-count:
     get:
       tags:
@@ -8807,6 +9023,30 @@ components:
           additionalProperties:
             type: string
           description: Header to attach to callback request.
+    CancelNexusOperationRequest:
+      type: object
+      properties:
+        namespace:
+          type: string
+          description: The namespace to authenticate to. This may be different from the target namespace of the specified endpoint.
+        identity:
+          type: string
+          description: The identity of the client who initiated this request.
+        endpoint:
+          type: string
+          description: Endpoint name, resolved via the Temporal service's endpoint registry.
+        service:
+          type: string
+          description: Nexus service name.
+        operation:
+          type: string
+          description: Nexus operation name.
+        operationToken:
+          type: string
+          description: Operation token from StartNexusOperationResponse.AsyncSuccess.
+    CancelNexusOperationResponse:
+      type: object
+      properties: {}
     CanceledFailureInfo:
       type: object
       properties:
@@ -13833,6 +14073,70 @@ components:
           allOf:
             - $ref: '#/components/schemas/Priority'
           description: Priority metadata
+    StartNexusOperationRequest:
+      type: object
+      properties:
+        namespace:
+          type: string
+          description: The namespace to authenticate to. This may be different from the target namespace of the specified endpoint.
+        identity:
+          type: string
+          description: The identity of the client who initiated this request.
+        requestId:
+          type: string
+          description: A unique identifier for this request, used as an idempotency key.
+        endpoint:
+          type: string
+          description: Endpoint name, resolved via the Temporal service's endpoint registry.
+        service:
+          type: string
+          description: Nexus service name.
+        operation:
+          type: string
+          description: Nexus operation name.
+        input:
+          allOf:
+            - $ref: '#/components/schemas/Payload'
+          description: Serialized input to the operation.
+        links:
+          type: array
+          items:
+            $ref: '#/components/schemas/Link'
+          description: Links for associating the caller with the operation.
+    StartNexusOperationResponse:
+      type: object
+      properties:
+        syncSuccess:
+          $ref: '#/components/schemas/StartNexusOperationResponse_SyncSuccess'
+        asyncSuccess:
+          $ref: '#/components/schemas/StartNexusOperationResponse_AsyncSuccess'
+        operationFailure:
+          $ref: '#/components/schemas/StartNexusOperationResponse_OperationFailure'
+        links:
+          type: array
+          items:
+            $ref: '#/components/schemas/Link'
+          description: Links associated with the operation, as returned by the handler.
+    StartNexusOperationResponse_AsyncSuccess:
+      type: object
+      properties:
+        operationToken:
+          type: string
+      description: An operation was started asynchronously. The token can be used for cancellation.
+    StartNexusOperationResponse_OperationFailure:
+      type: object
+      properties:
+        failure:
+          $ref: '#/components/schemas/Failure'
+      description: |-
+        The operation completed unsuccessfully.
+         The operation is considered canceled if the failure has a CanceledFailureInfo object attached.
+    StartNexusOperationResponse_SyncSuccess:
+      type: object
+      properties:
+        payload:
+          $ref: '#/components/schemas/Payload'
+      description: An operation completed successfully and synchronously.
     StartWorkflowExecutionRequest:
       type: object
       properties:
diff --git a/temporal/api/workflowservice/v1/request_response.proto b/temporal/api/workflowservice/v1/request_response.proto
index 4bf3272c6..970326556 100644
--- a/temporal/api/workflowservice/v1/request_response.proto
+++ b/temporal/api/workflowservice/v1/request_response.proto
@@ -2919,3 +2919,76 @@ message DeleteActivityExecutionRequest {
 
 message DeleteActivityExecutionResponse {
 }
+
+message StartNexusOperationRequest {
+    // The namespace to authenticate to. This may be different from the target namespace of the specified endpoint.
+    string namespace = 1;
+    // The identity of the client who initiated this request.
+    string identity = 2;
+    // A unique identifier for this request, used as an idempotency key.
+    string request_id = 3;
+
+    // Endpoint name, resolved via the Temporal service's endpoint registry.
+    string endpoint = 4;
+    // Nexus service name.
+    string service = 5;
+    // Nexus operation name.
+    string operation = 6;
+
+    // Serialized input to the operation.
+    temporal.api.common.v1.Payload input = 7;
+
+    // Links for associating the caller with the operation.
+    repeated temporal.api.common.v1.Link links = 8;
+
+    // TODO: The following fields will be supported in the future:
+    // - nexus_header: map<string, string> for Nexus request headers (tracing, etc.)
+    // - callback: string for async completion delivery URL
+    // - callback_header: map<string, string> for callback request headers
+}
+
+message StartNexusOperationResponse {
+    // An operation completed successfully and synchronously.
+    message SyncSuccess {
+        temporal.api.common.v1.Payload payload = 1;
+    }
+
+    // An operation was started asynchronously. The token can be used for cancellation.
+    message AsyncSuccess {
+        string operation_token = 1;
+    }
+
+    // The operation completed unsuccessfully.
+    // The operation is considered canceled if the failure has a CanceledFailureInfo object attached.
+    message OperationFailure {
+        temporal.api.failure.v1.Failure failure = 1;
+    }
+
+    oneof variant {
+        SyncSuccess sync_success = 1;
+        AsyncSuccess async_success = 2;
+        OperationFailure operation_failure = 3;
+    }
+
+    // Links associated with the operation, as returned by the handler.
+    repeated temporal.api.nexus.v1.Link links = 4;
+}
+
+message CancelNexusOperationRequest {
+    // The namespace to authenticate to. This may be different from the target namespace of the specified endpoint.
+    string namespace = 1;
+    // The identity of the client who initiated this request.
+    string identity = 2;
+
+    // Endpoint name, resolved via the Temporal service's endpoint registry.
+    string endpoint = 3;
+    // Nexus service name.
+    string service = 4;
+    // Nexus operation name.
+    string operation = 5;
+    // Operation token from StartNexusOperationResponse.AsyncSuccess.
+    string operation_token = 6;
+}
+
+message CancelNexusOperationResponse {
+}
diff --git a/temporal/api/workflowservice/v1/service.proto b/temporal/api/workflowservice/v1/service.proto
index c67a2717b..43726d9e2 100644
--- a/temporal/api/workflowservice/v1/service.proto
+++ b/temporal/api/workflowservice/v1/service.proto
@@ -1458,4 +1458,34 @@ service WorkflowService {
     // (-- api-linter: core::0127::http-annotation=disabled
     //     aip.dev/not-precedent: Activity deletion not exposed to HTTP, users should use cancel or terminate. --)
     rpc DeleteActivityExecution (DeleteActivityExecutionRequest) returns (DeleteActivityExecutionResponse) {}
+
+    // StartNexusOperation starts a Nexus operation on an endpoint, communicating directly with the
+    // endpoint using the caller's namespace credentials.
+    // The response follows the Nexus RPC spec semantics: synchronous completion, asynchronous start,
+    // or operation error.
+    // Handler errors (e.g., NOT_FOUND, BAD_REQUEST) are returned as gRPC errors.
+    rpc StartNexusOperation (StartNexusOperationRequest) returns (StartNexusOperationResponse) {
+        option (google.api.http) = {
+            post: "/namespaces/{namespace}/nexus-requests/endpoints/{endpoint}/services/{service}/operations/{operation}"
+            body: "*"
+            additional_bindings {
+                post: "/api/v1/namespaces/{namespace}/nexus-requests/endpoints/{endpoint}/services/{service}/operations/{operation}"
+                body: "*"
+            }
+        };
+    }
+
+    // CancelNexusOperation requests cancellation of a previously started asynchronous Nexus operation.
+    // Cancellation is cooperative: this forwards a cancel request to the handler, but the operation
+    // will only transition to canceled if the handler processes it.
+    rpc CancelNexusOperation (CancelNexusOperationRequest) returns (CancelNexusOperationResponse) {
+        option (google.api.http) = {
+            post: "/namespaces/{namespace}/nexus-requests/endpoints/{endpoint}/services/{service}/operations/{operation}/cancel"
+            body: "*"
+            additional_bindings {
+                post: "/api/v1/namespaces/{namespace}/nexus-requests/endpoints/{endpoint}/services/{service}/operations/{operation}/cancel"
+                body: "*"
+            }
+        };
+    }
 }