diff --git a/awscli/botocore/useragent.py b/awscli/botocore/useragent.py
index e3618150e322..51fddfb8bf2a 100644
--- a/awscli/botocore/useragent.py
+++ b/awscli/botocore/useragent.py
@@ -104,6 +104,7 @@
     'FLEXIBLE_CHECKSUMS_REQ_XXHASH3': 'AG',
     'FLEXIBLE_CHECKSUMS_REQ_XXHASH64': 'AH',
     'FLEXIBLE_CHECKSUMS_REQ_XXHASH128': 'AI',
+    'SSO_LOGIN_VANITY_URL': 'AM',
     'AGENTIC_CALLER_CLAUDE_CODE': 'AN',
     'AGENTIC_CALLER_GEMINI_CLI': 'AO',
     'AGENTIC_CALLER_CODEX': 'AP',
diff --git a/awscli/customizations/agenttoolkit/agents.py b/awscli/customizations/agenttoolkit/agents.py
index 4c38488f531b..7b2d13fc71f4 100644
--- a/awscli/customizations/agenttoolkit/agents.py
+++ b/awscli/customizations/agenttoolkit/agents.py
@@ -276,9 +276,6 @@ def __init__(self, agent, name, path):
         self.path = path
 
 
-# TODO: Verify detection, skills, and MCP config paths against actual
-# installations before release. Currently only tested with Kiro and
-# simulated agent directories.
 AGENT_CONFIGS = [
     # https://docs.anthropic.com/en/docs/claude-code/mcp
     AgentConfig(
diff --git a/awscli/customizations/configure/sso_commands.py b/awscli/customizations/configure/sso_commands.py
index cfd90a3beba8..3c7d0054127c 100644
--- a/awscli/customizations/configure/sso_commands.py
+++ b/awscli/customizations/configure/sso_commands.py
@@ -33,6 +33,7 @@
 from botocore.config import Config
 from botocore.configprovider import ConstantProvider
 from botocore.exceptions import ProfileNotFound
+from botocore.useragent import register_feature_id
 
 from awscli.customizations.configure import (
     get_section_header,
@@ -448,6 +449,7 @@ def _prompt_for_sso_start_url_and_sso_region(self, verify=None):
                 self._sso_session_prompter.sso_session_config['sso_region'] = (
                     region
                 )
+                register_feature_id('SSO_LOGIN_VANITY_URL')
                 return start_url, region, resolved_url
             except Exception as e:
                 logger.debug(
diff --git a/awscli/customizations/sso/login.py b/awscli/customizations/sso/login.py
index 3ad71608746f..99145a58c6bb 100644
--- a/awscli/customizations/sso/login.py
+++ b/awscli/customizations/sso/login.py
@@ -12,6 +12,8 @@
 # language governing permissions and limitations under the License.
 import os
 
+from botocore.useragent import register_feature_id
+
 from awscli.customizations.configure.writer import ConfigFileWriter
 from awscli.customizations.sso.resolve import resolve_start_url
 from awscli.customizations.sso.utils import (
@@ -62,6 +64,9 @@ def _run_main(self, parsed_args, parsed_globals):
             verify=verify,
         )
 
+        if resolved_url != start_url:
+            register_feature_id('SSO_LOGIN_VANITY_URL')
+
         on_pending_authorization = None
         if parsed_args.no_browser:
             on_pending_authorization = PrintOnlyHandler()
diff --git a/tests/functional/sso/test_login.py b/tests/functional/sso/test_login.py
index 6f618be0ef27..89d0a3612c03 100644
--- a/tests/functional/sso/test_login.py
+++ b/tests/functional/sso/test_login.py
@@ -15,6 +15,8 @@
 import os
 import re
 
+from botocore.context import start_as_current_context
+
 from awscli.testutils import mock
 from tests.functional.sso import BaseSSOTest
 
@@ -560,6 +562,12 @@ def test_config_not_rewritten_when_region_matches(self):
             config_content = f.read()
         self.assertIn('sso_region=us-east-1', config_content)
 
+    def test_vanity_url_sets_feature_id_in_user_agent(self):
+        self.add_oidc_auth_code_responses(self.access_token)
+        with start_as_current_context():
+            self.run_cmd('sso login')
+        self.assertIn('AM', self.last_request_dict['headers']['User-Agent'])
+
 
 class TestLoginWithVanityUrlLegacy(BaseSSOTest):
     def setUp(self):
@@ -628,3 +636,10 @@ def test_login_uses_configured_region(self):
         self.add_oidc_auth_code_responses(self.access_token)
         self.run_cmd('sso login')
         self.assert_used_expected_sso_region('us-west-2')
+
+    def test_direct_url_does_not_set_vanity_feature_id(self):
+        self.add_oidc_auth_code_responses(self.access_token)
+        with start_as_current_context():
+            self.run_cmd('sso login')
+        user_agent = self.last_request_dict['headers']['User-Agent']
+        self.assertNotIn('AM', user_agent.split('m/')[-1])