diff --git a/CHANGELOG.md b/CHANGELOG.md
index fc1430d38..108c730f7 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -12,6 +12,13 @@
   `type` / `value` / `text`. The existing `notes: list[str]` attribute is
   unchanged (it parses the separate legacy `<notes>` element still emitted by
   some job types). Fixes #1850.
+* Removed the pre-Tableau-8.3 XML namespace fallback
+  (`http://tableausoftware.com/api`). Every server TSC's `minimum_supported_server_version`
+  guard has ever admitted uses the current namespace (`http://tableau.com/api`),
+  and the runtime-detection code has been unreachable in practice for a
+  decade. `tableauserverclient.namespace` module and `UnknownNamespaceError`
+  are removed; the public `TSC.DEFAULT_NAMESPACE` re-export still works and
+  now points at `tableauserverclient.server.server.NAMESPACE`. Fixes #1046.
 
 ## 0.18.0 (6 April 2022)    
 * Switched to using defused_xml for xml attack protection
diff --git a/tableauserverclient/__init__.py b/tableauserverclient/__init__.py
index 7241f23ca..9b6ae5e34 100644
--- a/tableauserverclient/__init__.py
+++ b/tableauserverclient/__init__.py
@@ -1,5 +1,5 @@
 from tableauserverclient.bin._version import get_versions
-from tableauserverclient.namespace import NEW_NAMESPACE as DEFAULT_NAMESPACE
+from tableauserverclient.server.server import NAMESPACE as DEFAULT_NAMESPACE
 from tableauserverclient.models import (
     BackgroundJobItem,
     CollectionItem,
diff --git a/tableauserverclient/namespace.py b/tableauserverclient/namespace.py
deleted file mode 100644
index 54ac46d8d..000000000
--- a/tableauserverclient/namespace.py
+++ /dev/null
@@ -1,37 +0,0 @@
-import re
-
-from defusedxml.ElementTree import fromstring
-
-OLD_NAMESPACE = "http://tableausoftware.com/api"
-NEW_NAMESPACE = "http://tableau.com/api"
-NAMESPACE_RE = re.compile(r"\{(.*?)\}")
-
-
-class UnknownNamespaceError(Exception):
-    pass
-
-
-class Namespace:
-    def __init__(self):
-        self._namespace = {"t": NEW_NAMESPACE}
-        self._detected = False
-
-    def __call__(self):
-        return self._namespace
-
-    def detect(self, xml):
-        if self._detected:
-            return
-
-        if not xml.startswith(b"<?xml"):
-            return  # Not an xml file, don't detect anything
-
-        root = fromstring(xml)
-        matches = NAMESPACE_RE.match(root.tag)
-        if matches:
-            detected_ns = matches.group(1)
-            if detected_ns in (OLD_NAMESPACE, NEW_NAMESPACE):
-                self._namespace = {"t": detected_ns}
-                self._detected = True
-            else:
-                raise UnknownNamespaceError(detected_ns)
diff --git a/tableauserverclient/server/endpoint/auth_endpoint.py b/tableauserverclient/server/endpoint/auth_endpoint.py
index fe0c9b3da..0baf4d0e2 100644
--- a/tableauserverclient/server/endpoint/auth_endpoint.py
+++ b/tableauserverclient/server/endpoint/auth_endpoint.py
@@ -80,7 +80,6 @@ def sign_in(self, auth_req: "Credentials") -> contextmgr:
                 **self.parent_srv.http_options,
                 allow_redirects=False,
             )
-        self.parent_srv._namespace.detect(server_response.content)
         self._check_status(server_response, url)
         parsed_response = fromstring(server_response.content)
         site_id = parsed_response.find(".//t:site", namespaces=self.parent_srv.namespace).get("id", None)
@@ -154,7 +153,6 @@ def switch_site(self, site_item: "SiteItem") -> contextmgr:
                 return Auth.contextmgr(self.sign_out)
             else:
                 raise e
-        self.parent_srv._namespace.detect(server_response.content)
         self._check_status(server_response, url)
         parsed_response = fromstring(server_response.content)
         site_id = parsed_response.find(".//t:site", namespaces=self.parent_srv.namespace).get("id", None)
diff --git a/tableauserverclient/server/endpoint/endpoint.py b/tableauserverclient/server/endpoint/endpoint.py
index 31a0806dc..a6adf830d 100644
--- a/tableauserverclient/server/endpoint/endpoint.py
+++ b/tableauserverclient/server/endpoint/endpoint.py
@@ -152,9 +152,6 @@ def _make_request(
         # BE CAREFUL WHEN SHARING THESE RESULTS - MAY CONTAIN YOUR SENSITIVE DATA
         # logger.debug(loggable_response)
 
-        if content_type == "application/xml":
-            self.parent_srv._namespace.detect(server_response.content)
-
         return server_response
 
     def _check_status(self, server_response: "Response", url: str | None = None):
diff --git a/tableauserverclient/server/server.py b/tableauserverclient/server/server.py
index 6b0338970..d28e3723e 100644
--- a/tableauserverclient/server/server.py
+++ b/tableauserverclient/server/server.py
@@ -46,7 +46,6 @@
     EndpointUnavailableError,
 )
 from tableauserverclient.server.endpoint.exceptions import NotSignedInError
-from tableauserverclient.namespace import Namespace
 
 _PRODUCT_TO_REST_VERSION = {
     "10.0": "2.3",
@@ -59,6 +58,11 @@
 minimum_supported_server_version = "2.3"
 default_server_version = "2.4"  # first version that dropped the legacy auth endpoint
 
+# The REST API has used the "http://tableau.com/api" XML namespace since Tableau
+# Server 8.3 (2015). Callers on older servers are unsupported.
+NAMESPACE = "http://tableau.com/api"
+_NAMESPACE_MAP = {"t": NAMESPACE}
+
 
 class Server:
     """
@@ -176,7 +180,6 @@ def __init__(self, server_address, use_server_version=False, http_options=None,
         self.data_acceleration_report = DataAccelerationReport(self)
         self.data_alerts = DataAlerts(self)
         self.fileuploads = Fileuploads(self)
-        self._namespace = Namespace()
         self.flow_runs = FlowRuns(self)
         self.metrics = Metrics(self)
         self.custom_views = CustomViews(self)
@@ -290,7 +293,7 @@ def baseurl(self):
 
     @property
     def namespace(self):
-        return self._namespace()
+        return dict(_NAMESPACE_MAP)
 
     @property
     def auth_token(self):