diff --git a/README.md b/README.md
index 254794b..4866ece 100644
--- a/README.md
+++ b/README.md
@@ -17,8 +17,15 @@ from VDDK 8 NBD traffic; see `docs/`.
 
 ## Status
 
-Implemented against vCenter 8 / ESXi 8. Default transport is `nbdssl`
-(`nbd` is still available):
+Supported and tested on **vCenter 8 / ESXi 8** (lab: 8.0.1). The
+VixDiskLib compatibility mode is `8.0` only. VIM login requests
+pyVmomi's vim25 **8.x** versions, so a newer host such as vSphere 9 stays
+on 8.x SOAP instead of 9.x types.
+
+vSphere 9 is untested. vCenter / ESXi 7 and earlier are not supported at the
+moment.
+
+Default transport is `nbdssl` (`nbd` is still available):
 
 - `VixDiskLib_ConnectEx` (UID credentials)
 - `VixDiskLib_Open` (datastore path, read-only or read-write)
diff --git a/docs/nfc_auth.md b/docs/nfc_auth.md
index e19b515..36e89ed 100644
--- a/docs/nfc_auth.md
+++ b/docs/nfc_auth.md
@@ -51,7 +51,9 @@ rather than crafting SOAP.
 
 - Endpoint: `https://<vcenter>:443/sdk`
 - Cookie: `vmware_soap_session`
-- SOAPAction: `"urn:vim25/8.0.1.0"` (negotiated)
+- SOAPAction: newest advertised 8.x (`SmartConnect` `preferredApiVersions`
+  is capped at `vim.version.v8_*` so a vSphere 9 host does not pick
+  pyVmomi 9 types). Lab vCenter 8.0.1 used `"urn:vim25/8.0.1.0"`.
 
 VDDK logs this as `Connected to VIM Server` / `Authenticating user` /
 `Logged in!`. OpenVixDiskLib keeps that `ServiceInstance` and
diff --git a/openvixdisklib/nfc_auth.py b/openvixdisklib/nfc_auth.py
index 49d85aa..d50744a 100644
--- a/openvixdisklib/nfc_auth.py
+++ b/openvixdisklib/nfc_auth.py
@@ -24,7 +24,12 @@
 
 from pyVim.connect import Disconnect, SmartConnect
 from pyVmomi import vim
-from pyVmomi.VmomiSupport import F_OPTIONAL, CreateManagedType, GetVmodlType
+from pyVmomi.VmomiSupport import (
+    F_OPTIONAL,
+    CreateManagedType,
+    GetServiceVersions,
+    GetVmodlType,
+)
 
 NFC_SERVICE_MOID = "nfcService"
 AUTHD_DEFAULT_PORT = 902
@@ -132,6 +137,24 @@ def nfc_service(si: vim.ServiceInstance) -> vim.NfcService:
     return nfc_cls(NFC_SERVICE_MOID, si._stub)
 
 
+def _vim_preferred_api_versions() -> list[str]:
+    """Return pyVmomi vim25 8.x versions, newest first.
+
+    ``SmartConnect`` otherwise walks every version this pyVmomi knows,
+    including 9.x, so a vSphere 9 host would negotiate 9.x SOAP. NFC
+    was reverse-engineered on vSphere 8; keep that family so newer
+    hosts stay on an 8.x ``SOAPAction`` they still advertise.
+    """
+    versions = [
+        v for v in GetServiceVersions("vim25") if v.startswith("vim.version.v8_")
+    ]
+    if not versions:
+        raise RuntimeError(
+            "pyVmomi does not provide vim25 8.x types; OpenVixDiskLib requires them"
+        )
+    return versions
+
+
 def connect_vim(
     host: str,
     username: str,
@@ -171,6 +194,7 @@ def connect_vim(
         thumbprint=thumbprint,
         sslContext=ssl_context,
         disableSslCertValidation=skip_ca,
+        preferredApiVersions=_vim_preferred_api_versions(),
     )