diff --git a/app/models/concerns/has_user_type.rb b/app/models/concerns/has_user_type.rb
index 2aba5d156e1be89e0975ee790f9fbe86c7918879..ea3ba1a1a9abae9df959fc368d0586020e6ddc17 100644
--- a/app/models/concerns/has_user_type.rb
+++ b/app/models/concerns/has_user_type.rb
@@ -47,6 +47,7 @@ module HasUserType
   # Changes to these types might have billing implications, https://docs.gitlab.com/ee/subscriptions/gitlab_com/#billable-users
   NON_INTERNAL_USER_TYPES = %w[human project_bot service_user service_account].freeze
   INTERNAL_USER_TYPES = (USER_TYPES.keys - NON_INTERNAL_USER_TYPES).freeze
+  INSTANCE_USER_TYPES = (INTERNAL_USER_TYPES - [:duo_code_review_bot]).freeze
 
   included do
     enum user_type: USER_TYPES
@@ -72,6 +73,14 @@ def internal?
     INTERNAL_USER_TYPES.include?(user_type)
   end
 
+  # rubocop:disable Gitlab/AvoidGitlabInstanceChecks -- This is not related to a specific feature
+  def instance_user?
+    return !Gitlab.com? if user_type == 'service_account'
+
+    INSTANCE_USER_TYPES.include?(user_type)
+  end
+  # rubocop:enable Gitlab/AvoidGitlabInstanceChecks
+
   def redacted_name(viewing_user)
     return self.name unless self.project_bot?
 
diff --git a/app/models/user.rb b/app/models/user.rb
index ccd4c95a205bc5e15f6e8648caff1d77af97d6bf..ea2a2d7fc57b461a27a668907f389d2a3a5f2038 100644
--- a/app/models/user.rb
+++ b/app/models/user.rb
@@ -1062,7 +1062,7 @@ def find_by_ssh_key_id(key_id)
 
     def find_by_full_path(path, follow_redirects: false)
       namespace = Namespace.user_namespaces.find_by_full_path(path, follow_redirects: follow_redirects)
-      namespace&.owner
+      namespace&.owner || find_by_username(path)
     end
 
     def reference_prefix
diff --git a/ee/app/models/ee/user.rb b/ee/app/models/ee/user.rb
index a766e1da29a0001cd2a26b503b73ef7dac379cef..f717baab8dd45fc8affd7c00346ff297a152cc8b 100644
--- a/ee/app/models/ee/user.rb
+++ b/ee/app/models/ee/user.rb
@@ -44,9 +44,19 @@ module User
       after_create :associate_with_enterprise_group
       after_update :email_changed_hook, if: :saved_change_to_email?
 
-      delegate :shared_runners_minutes_limit, :shared_runners_minutes_limit=,
-        :extra_shared_runners_minutes_limit, :extra_shared_runners_minutes_limit=,
+      delegate :shared_runners_minutes_limit=,
+        :extra_shared_runners_minutes_limit=,
         to: :namespace
+
+      # PoC branch: this address http 500 errors with users API
+      def shared_runners_minutes_limit
+        namespace&.shared_runners_minutes_limit
+      end
+
+      def extra_shared_runners_minutes_limit
+        namespace&.extra_shared_runners_minutes_limit
+      end
+
       delegate :provisioned_by_group, :provisioned_by_group=,
         :provisioned_by_group_id, :provisioned_by_group_id=,
         :onboarding_status_step_url, :onboarding_status_step_url=,
diff --git a/ee/spec/lib/ee/users/internal_spec.rb b/ee/spec/lib/ee/users/internal_spec.rb
index f5fade809e8d6e12c5fe1669c0fafc07cc8c173d..dcd30c2a632b4453a5b228a443c80654708f29f3 100644
--- a/ee/spec/lib/ee/users/internal_spec.rb
+++ b/ee/spec/lib/ee/users/internal_spec.rb
@@ -10,12 +10,6 @@
       end.to change { User.where(user_type: bot_type).count }.by(1)
     end
 
-    it 'creates a route for the namespace of the created user' do
-      bot_user = described_class.public_send(bot_type)
-
-      expect(bot_user.namespace.route).to be_present
-    end
-
     it 'does not create a new user if it already exists' do
       described_class.public_send(bot_type)
 
diff --git a/ee/spec/services/ee/merge_requests/update_service_spec.rb b/ee/spec/services/ee/merge_requests/update_service_spec.rb
index 053dbf106e44d51158c02254e2a94a8ef53fa5c5..1c468b6b9e70312f90eabb2a0a43e0f1866c4f77 100644
--- a/ee/spec/services/ee/merge_requests/update_service_spec.rb
+++ b/ee/spec/services/ee/merge_requests/update_service_spec.rb
@@ -599,7 +599,7 @@ def update_merge_request(opts)
             old_associations: {
               approval_rules: [],
               labels: [],
-              mentioned_users: [],
+              mentioned_users: [user2],
               assignees: [user3],
               closing_issues_ids: [],
               reviewers: [],
diff --git a/lib/banzai/filter/references/user_reference_filter.rb b/lib/banzai/filter/references/user_reference_filter.rb
index bce181b6a882d10490ffacb37dbd8c45fce4b6a2..518e7a28dff3c5fe5d5ca829b38624b041d62851 100644
--- a/lib/banzai/filter/references/user_reference_filter.rb
+++ b/lib/banzai/filter/references/user_reference_filter.rb
@@ -51,6 +51,8 @@ def object_link_filter(text, pattern, link_content: nil, link_reference: false)
               cached_call(:banzai_url_for_object, match, path: [User, username.downcase]) do
                 if namespace = namespaces[username.downcase]
                   link_to_namespace(namespace, link_content: link_content) || match
+                elsif user = users[username.downcase]
+                  link_to_user(user, link_content: link_content)
                 else
                   match
                 end
@@ -71,6 +73,10 @@ def namespaces
                           .transform_keys(&:downcase)
         end
 
+        def users
+          @users ||= User.by_username(usernames).index_by(&:username).transform_keys(&:downcase)
+        end
+
         # Returns all usernames referenced in the current document.
         def usernames
           refs = Set.new
@@ -106,7 +112,7 @@ def link_to_namespace(namespace, link_content: nil)
           if namespace.is_a?(Group)
             link_to_group(namespace.full_path, namespace, link_content: link_content)
           else
-            link_to_user(namespace.path, namespace, link_content: link_content)
+            link_to_user(namespace.owner, link_content: link_content)
           end
         end
 
@@ -118,12 +124,12 @@ def link_to_group(group, namespace, link_content: nil)
           link_tag(url, data, content, namespace.full_name)
         end
 
-        def link_to_user(user, namespace, link_content: nil)
+        def link_to_user(user, link_content: nil)
           url = urls.user_url(user, only_path: context[:only_path])
-          data = data_attribute(user: namespace.owner_id)
-          content = link_content || (User.reference_prefix + user)
+          data = data_attribute(user: user.id)
+          content = link_content || (User.reference_prefix + user.username)
 
-          link_tag(url, data, content, namespace.owner_name)
+          link_tag(url, data, content, user.username)
         end
 
         def link_tag(url, data, link_content, title)
diff --git a/lib/users/internal.rb b/lib/users/internal.rb
index cc38f6517cd62c8194a1ee79d32290a495a09235..377bd05fa0acfe1ccdac1e7cfb2122e1968893ec 100644
--- a/lib/users/internal.rb
+++ b/lib/users/internal.rb
@@ -174,11 +174,6 @@ def create_unique_internal(scope, username, email_pattern, &creation_block)
           &creation_block
         )
 
-        # https://gitlab.com/gitlab-org/gitlab/-/issues/442780
-        organization = ::Organizations::Organization.first
-        user.assign_personal_namespace(organization)
-        user.organizations << organization
-
         Users::UpdateService.new(user, user: user).execute(validate: false)
         user
       ensure
diff --git a/spec/features/admin/admin_users_impersonation_tokens_spec.rb b/spec/features/admin/admin_users_impersonation_tokens_spec.rb
index 6b058ef31040e0a0c005bb21b2a8d9d2f6ca0d0b..e82d98b1f072cacfdce18ad32ba8bb447187f7e8 100644
--- a/spec/features/admin/admin_users_impersonation_tokens_spec.rb
+++ b/spec/features/admin/admin_users_impersonation_tokens_spec.rb
@@ -8,7 +8,7 @@
 
   let(:organization) { create(:organization) }
   let(:admin) { create(:admin, organizations: [organization]) }
-  let!(:user) { create(:user, organizations: [organization]) }
+  let!(:user) { create(:user, :with_namespace, organizations: [organization]) }
 
   before do
     sign_in(admin)
diff --git a/spec/lib/banzai/filter/references/user_reference_filter_spec.rb b/spec/lib/banzai/filter/references/user_reference_filter_spec.rb
index d37993cb316b76d3f84e1146bd3b2ddbe34df2b6..c0f7d4c5ce022958643b1d5593d28fe00f1106d0 100644
--- a/spec/lib/banzai/filter/references/user_reference_filter_spec.rb
+++ b/spec/lib/banzai/filter/references/user_reference_filter_spec.rb
@@ -230,7 +230,7 @@ def get_reference(user)
     let(:reference3) { group.to_reference }
 
     it 'does not have N+1 per multiple user references', :use_sql_query_cache do
-      markdown = reference.to_s
+      markdown = "#{reference} @qwertyuiopzx"
       reference_filter(markdown) # warm up
 
       control_count = ActiveRecord::QueryRecorder.new(skip_cached: false) do
diff --git a/spec/lib/gitlab/background_migration/delete_orphaned_groups_spec.rb b/spec/lib/gitlab/background_migration/delete_orphaned_groups_spec.rb
index 4d34cb55602792a32ce3add06ddbae0617c4b7a2..fdc2c91d9269deb3f4e27640230deb643bfb44fb 100644
--- a/spec/lib/gitlab/background_migration/delete_orphaned_groups_spec.rb
+++ b/spec/lib/gitlab/background_migration/delete_orphaned_groups_spec.rb
@@ -55,7 +55,7 @@
     it 'enqueues ::GroupDestroyWorker for each group whose parent\'s do not exist and destroys them', :sidekiq_inline do
       parent.destroy!
 
-      expect { background_migration }.to change { namespaces.count }.from(10).to(6)
+      expect { background_migration }.to change { namespaces.count }.from(9).to(5)
         .and change { namespaces.where(id: orphaned_groups.pluck(:id)).count }.from(4).to(0)
     end
   end
diff --git a/spec/lib/users/internal_spec.rb b/spec/lib/users/internal_spec.rb
index 0e8ab182a3f0c5522a3e8edaaf1d72a75d5b3970..86ae3415cd5966baf28a87f9c7ab8a830715f06b 100644
--- a/spec/lib/users/internal_spec.rb
+++ b/spec/lib/users/internal_spec.rb
@@ -3,8 +3,6 @@
 require 'spec_helper'
 
 RSpec.describe Users::Internal, feature_category: :user_profile do
-  let_it_be(:organization) { create(:organization) }
-
   shared_examples 'bot users' do |bot_type, username, email|
     it 'creates the user if it does not exist' do
       expect do
@@ -12,19 +10,6 @@
       end.to change { User.where(user_type: bot_type).count }.by(1)
     end
 
-    it 'creates a route for the namespace of the created user' do
-      bot_user = described_class.public_send(bot_type)
-
-      expect(bot_user.namespace.route).to be_present
-      expect(bot_user.namespace.organization).to eq(organization)
-    end
-
-    it 'assigns the first found organization to the created user' do
-      bot_user = described_class.public_send(bot_type)
-
-      expect(bot_user.organizations.first).to eq(organization)
-    end
-
     it 'does not create a new user if it already exists' do
       described_class.public_send(bot_type)
 
diff --git a/spec/models/concerns/has_user_type_spec.rb b/spec/models/concerns/has_user_type_spec.rb
index fc619485d0a48b81956dabc9c8dab630cbac472b..a8a90ea514b95695b4504b79fc7617393b8caa4c 100644
--- a/spec/models/concerns/has_user_type_spec.rb
+++ b/spec/models/concerns/has_user_type_spec.rb
@@ -9,6 +9,7 @@
   let(:bots) { User::BOT_USER_TYPES.map { |type| public_send(type) } }
   let(:non_internal) { User::NON_INTERNAL_USER_TYPES.map { |type| public_send(type) } }
   let(:everyone) { User::USER_TYPES.keys.map { |type| public_send(type) } }
+  let(:instance) { User::INSTANCE_USER_TYPES.map { |type| public_send(type) } }
 
   specify 'types consistency checks', :aggregate_failures do
     expect(described_class::USER_TYPES.keys)
@@ -204,5 +205,28 @@
         end
       end
     end
+
+    describe 'instance_user?' do
+      context 'when on SaaS', :saas do
+        it 'is true for all instance user types and false for others' do
+          expect(instance).to all(be_instance_user)
+
+          (everyone - instance).each do |user|
+            expect(user.instance_user?).to be(false)
+          end
+        end
+      end
+
+      context 'when on Self Managed' do
+        it 'is true for service_account and all instance user types and false for others' do
+          expect(instance).to all(be_instance_user)
+          expect(service_account.instance_user?).to be(true)
+
+          (everyone - instance - [service_account]).each do |user|
+            expect(user.instance_user?).to be(false)
+          end
+        end
+      end
+    end
   end
 end