diff --git a/CHANGELOG.md b/CHANGELOG.md
index d4a709673..fd6064a82 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -42,6 +42,7 @@ Inspired from [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 - Added `file` to `/_cache/clear` and `/{index}/_cache/clear` ([#396](https://github.com/opensearch-project/opensearch-api-specification/pull/396))
 - Added a workflow to run tests against the next version of OpenSearch ([#409](https://github.com/opensearch-project/opensearch-api-specification/pull/409))
 - Added support for skipping tests using semver range ([#410](https://github.com/opensearch-project/opensearch-api-specification/pull/410))
+- Added `cluster_manager_timeout` to `HEAD /{index}` ([#421](https://github.com/opensearch-project/opensearch-api-specification/pull/421))
 
 ### Changed
 
diff --git a/spec/namespaces/indices.yaml b/spec/namespaces/indices.yaml
index 1ba7e4a5c..dc113533b 100644
--- a/spec/namespaces/indices.yaml
+++ b/spec/namespaces/indices.yaml
@@ -894,6 +894,7 @@ paths:
       parameters:
         - $ref: '#/components/parameters/indices.exists::path.index'
         - $ref: '#/components/parameters/indices.exists::query.allow_no_indices'
+        - $ref: '#/components/parameters/indices.exists::query.cluster_manager_timeout'
         - $ref: '#/components/parameters/indices.exists::query.expand_wildcards'
         - $ref: '#/components/parameters/indices.exists::query.flat_settings'
         - $ref: '#/components/parameters/indices.exists::query.ignore_unavailable'
@@ -3220,6 +3221,13 @@ components:
       schema:
         $ref: '../schemas/_common.yaml#/components/schemas/Indices'
       style: simple
+    indices.exists::query.cluster_manager_timeout:
+      name: cluster_manager_timeout
+      in: query
+      description: Operation timeout for connection to cluster-manager node.
+      schema:
+        $ref: '../schemas/_common.yaml#/components/schemas/Duration'
+      x-version-added: '2.0'
     indices.exists::query.allow_no_indices:
       in: query
       name: allow_no_indices