diff --git a/config.py b/config.py
index 005ea4880..2a4d1cceb 100644
--- a/config.py
+++ b/config.py
@@ -273,6 +273,9 @@ class DefaultConfig(ImmutableConfig):
   # rather than only write access or admin access.
   FEATURE_READER_BUILD_LOGS = False
 
+  # Feature Flag: If set to true, autocompletion will apply to partial usernames.
+  FEATURE_PARTIAL_USER_AUTOCOMPLETE = True
+
   # If a namespace is defined in the public namespace list, then it will appear on *all*
   # user's repository list pages, regardless of whether that user is a member of the namespace.
   # Typically, this is used by an enterprise customer in configuring a set of "well-known"
diff --git a/data/model/user.py b/data/model/user.py
index 758491ef1..6e8265f69 100644
--- a/data/model/user.py
+++ b/data/model/user.py
@@ -605,8 +605,12 @@ def get_matching_user_namespaces(namespace_prefix, username, limit=10):
 
   return _basequery.filter_to_repos_for_user(base_query, username).limit(limit)
 
-def get_matching_users(username_prefix, robot_namespace=None, organization=None, limit=20):
+def get_matching_users(username_prefix, robot_namespace=None, organization=None, limit=20,
+                       exact_matches_only=False):
   user_search =  prefix_search(User.username, username_prefix)
+  if exact_matches_only:
+    user_search = (User.username == username_prefix)
+
   direct_user_query = (user_search & (User.organization == False) & (User.robot == False))
 
   if robot_namespace:
diff --git a/endpoints/api/search.py b/endpoints/api/search.py
index 8fe3de3ba..204b055c5 100644
--- a/endpoints/api/search.py
+++ b/endpoints/api/search.py
@@ -1,5 +1,7 @@
 """ Conduct searches against all registry context. """
 
+import features
+
 from endpoints.api import (ApiResource, parse_args, query_param, truthy_bool, nickname, resource,
                            require_scope, path_param, internal_only, Unauthorized, InvalidRequest,
                            show_if)
@@ -107,7 +109,8 @@ class EntitySearch(ApiResource):
           robot_namespace = namespace_name
 
     # Lookup users in the database for the prefix query.
-    users = model.user.get_matching_users(prefix, robot_namespace, organization, limit=10)
+    users = model.user.get_matching_users(prefix, robot_namespace, organization, limit=10,
+                                          exact_matches_only=not features.PARTIAL_USER_AUTOCOMPLETE)
 
     # Lookup users via the user system for the prefix query. We'll filter out any users that
     # already exist in the database.
diff --git a/static/directives/config/config-setup-tool.html b/static/directives/config/config-setup-tool.html
index 09368ba1f..d8fc2b800 100644
--- a/static/directives/config/config-setup-tool.html
+++ b/static/directives/config/config-setup-tool.html
@@ -1239,6 +1239,17 @@
               </div>
             </td>
           </tr>
+          <tr>
+            <td class="non-input">Prefix username autocompletion:</td>
+            <td colspan="2">
+              <div class="config-bool-field" binding="config.FEATURE_PARTIAL_USER_AUTOCOMPLETE">
+                Allow prefix username autocompletion
+              </div>
+              <div class="help-text">
+                 If disabled, autocompletion for users will only match on exact usernames.
+              </div>
+            </td>
+          </tr>
           <tr ng-show="config.FEATURE_MAILING">
             <td class="non-input">Team Invitations:</td>
             <td colspan="2">
diff --git a/test/test_api_usage.py b/test/test_api_usage.py
index 06f533612..49259e7a3 100644
--- a/test/test_api_usage.py
+++ b/test/test_api_usage.py
@@ -1017,6 +1017,23 @@ class TestGetMatchingEntities(ApiTestCase):
     assert 'outsideorg' in names
     assert not 'owners' in names
 
+  def test_prefix_disabled(self):
+    with patch('features.PARTIAL_USER_AUTOCOMPLETE', False):
+      self.login(NO_ACCESS_USER)
+
+      json = self.getJsonResponse(EntitySearch, params=dict(prefix='o', namespace=ORGANIZATION,
+                                                            includeTeams='true'))
+
+      names = set([r['name'] for r in json['results']])
+      assert not 'outsideorg' in names
+      assert not 'owners' in names 
+
+      json = self.getJsonResponse(EntitySearch, params=dict(prefix='outsideorg', namespace=ORGANIZATION,
+                                                            includeTeams='true'))
+      names = set([r['name'] for r in json['results']])
+      assert 'outsideorg' in names
+      assert not 'owners' in names
+
   def test_inorg(self):
     self.login(ADMIN_ACCESS_USER)
 
diff --git a/util/config/configutil.py b/util/config/configutil.py
index 7db5d4578..ace6e02a5 100644
--- a/util/config/configutil.py
+++ b/util/config/configutil.py
@@ -20,6 +20,7 @@ def add_enterprise_config_defaults(config_obj, current_secret_key, hostname):
   config_obj['FEATURE_CHANGE_TAG_EXPIRATION'] = config_obj.get('FEATURE_CHANGE_TAG_EXPIRATION',
                                                                True)
   config_obj['FEATURE_DIRECT_LOGIN'] = config_obj.get('FEATURE_DIRECT_LOGIN', True)
+  config_obj['FEATURE_PARTIAL_USER_AUTOCOMPLETE'] = config_obj.get('FEATURE_PARTIAL_USER_AUTOCOMPLETE', True)
 
   # Default features that are off.
   config_obj['FEATURE_MAILING'] = config_obj.get('FEATURE_MAILING', False)