diff --git a/api/v3/api_constants.py b/api/v3/api_constants.py
new file mode 100644
index 0000000..9752242
--- /dev/null
+++ b/api/v3/api_constants.py
@@ -0,0 +1,28 @@
+# Copyright 2020 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style
+# license that can be found in the LICENSE file.
+"""Some constants used by Monorail's v3 API."""
+
+# Max comments per page in the ListComment API.
+MAX_COMMENTS_PER_PAGE = 100
+
+# Max issues per page in the SearchIssues API.
+MAX_ISSUES_PER_PAGE = 100
+
+# Max issues tp fetch in the BatchGetIssues API.
+MAX_BATCH_ISSUES = 100
+
+# Max issues to modify at once in the ModifyIssues API.
+MAX_MODIFY_ISSUES = 100
+
+# Max impacted issues allowed in a ModifyIssues API.
+MAX_MODIFY_IMPACTED_ISSUES = 50
+
+# Max approval values to modify at once in the ModifyIssueApprovalValues API.
+MAX_MODIFY_APPROVAL_VALUES = 100
+
+# Max users to fetch in the BatchGetUsers API.
+MAX_BATCH_USERS = 100
+
+# Max component defs to fetch in the ListComponentDefs API
+MAX_COMPONENTS_PER_PAGE = 100