diff --git a/spec/batch.yaml b/spec/batch.yaml
index e83d938e..e0e2668c 100644
--- a/spec/batch.yaml
+++ b/spec/batch.yaml
@@ -58,6 +58,18 @@ paths:
             For alignment jobs, the text file that the data file should be aligned to.
           required: false
           type: file
+        - name: X-SM-Processing-Data
+          in: header
+          type: string
+          required: false
+          description: >-
+            **Note**: Only available for on-prem
+
+            JSON dictionary of processing settings for the job worker.
+            Currently supports `parallel_engines` (integer), which controls
+            the number of engines the worker can use in parallel for this job, and
+            `user_id` (string), which is the user id for this job.
+            Example: `{"parallel_engines": 4}`
       responses:
         "201":
           description: OK
@@ -1082,7 +1094,7 @@ definitions:
               additionalProperties: false
               type: object
               required:
-                - from 
+                - from
                 - to
               properties:
                 from: