diff --git a/CLAUDE.md b/CLAUDE.md
index b91d57e..4e3939b 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -94,8 +94,7 @@ End-to-end chain working from a pure managed .NET 10 client: `Hist.GetV → Hist
 Smaller, isolated items — none block the production read surface:
 
 - Remote TCP transports (`RemoteTcpIntegrated`, `RemoteTcpCertificate`) untested against an actual remote Historian (tests skip without `HISTORIAN_REMOTE_TCP_HOST`).
-- Explicit username/password tag-metadata path (`HistorianWcfTagClient` line ~357) throws — only integrated security wired for that op.
-- `Historian2020ProtocolDialect.GetTagInfoByName/GetTagInfos` throws — currently dead code; `GetTagMetadataAsync` works through the WCF tag client instead.
+- Explicit username/password tag-metadata path is wired (validator only blocks no-auth-at-all), but live-verification requires `HISTORIAN_USER`+`HISTORIAN_PASSWORD` set; gated test `GetTagMetadataAsync_ExplicitCredentials_AgainstLocalHistorian` skips otherwise.
 - Per-row trailing ~24 bytes of `GetNextQueryResultBuffer` are not decoded (likely per-sample value/source/state metadata).
 - `EnsureTagAsync` distinct `MinRaw`/`MaxRaw` persistence requires `ApplyScaling=true` + a follow-up `UpdateTags` call — not yet wired (no API user has asked).
 
diff --git a/src/AVEVA.Historian.Client/Protocol/Historian2020ProtocolDialect.cs b/src/AVEVA.Historian.Client/Protocol/Historian2020ProtocolDialect.cs
index 38d64f4..8c5bb04 100644
--- a/src/AVEVA.Historian.Client/Protocol/Historian2020ProtocolDialect.cs
+++ b/src/AVEVA.Historian.Client/Protocol/Historian2020ProtocolDialect.cs
@@ -87,17 +87,6 @@ internal sealed class Historian2020ProtocolDialect
 #pragma warning restore CA1416
     }
 
-    public IAsyncEnumerable<string> BrowseTagNamesAsync(string filter, CancellationToken cancellationToken)
-    {
-        return Missing<string>("StartLikeTagNameSearch/GetLikeTagnames", cancellationToken);
-    }
-
-    public Task<HistorianTagMetadata?> GetTagMetadataAsync(string tag, CancellationToken cancellationToken)
-    {
-        cancellationToken.ThrowIfCancellationRequested();
-        throw new ProtocolEvidenceMissingException("GetTagInfoByName/GetTagInfos");
-    }
-
     public Task<HistorianConnectionStatus> GetConnectionStatusAsync(CancellationToken cancellationToken)
     {
         cancellationToken.ThrowIfCancellationRequested();
diff --git a/src/AVEVA.Historian.Client/Wcf/HistorianWcfTagClient.cs b/src/AVEVA.Historian.Client/Wcf/HistorianWcfTagClient.cs
index 74ad591..e126298 100644
--- a/src/AVEVA.Historian.Client/Wcf/HistorianWcfTagClient.cs
+++ b/src/AVEVA.Historian.Client/Wcf/HistorianWcfTagClient.cs
@@ -351,10 +351,18 @@ internal static class HistorianWcfTagClient
 
         private static void ValidateSupportedAuth(HistorianClientOptions options)
         {
+            // Three valid auth shapes:
+            //   1. IntegratedSecurity=true (current Windows identity, no UserName/Password)
+            //   2. IntegratedSecurity=false + UserName + Password (NTLM/Kerberos with explicit creds)
+            //   3. IntegratedSecurity=true + UserName + Password (impersonation/explicit override)
+            // The fourth combination — IntegratedSecurity=false with no UserName/Password — has
+            // no way to authenticate against the /Hist-Integrated endpoint and is rejected.
             if (!options.IntegratedSecurity
-                && (!string.IsNullOrEmpty(options.UserName) || !string.IsNullOrEmpty(options.Password)))
+                && string.IsNullOrEmpty(options.UserName)
+                && string.IsNullOrEmpty(options.Password))
             {
-                throw new ProtocolEvidenceMissingException("Open2 explicit username/password tag browse");
+                throw new ProtocolEvidenceMissingException(
+                    "Tag browse / metadata requires either IntegratedSecurity=true OR an explicit UserName + Password.");
             }
         }
 
diff --git a/tests/AVEVA.Historian.Client.Tests/HistorianClientIntegrationTests.cs b/tests/AVEVA.Historian.Client.Tests/HistorianClientIntegrationTests.cs
index 2fe5426..0e82e0a 100644
--- a/tests/AVEVA.Historian.Client.Tests/HistorianClientIntegrationTests.cs
+++ b/tests/AVEVA.Historian.Client.Tests/HistorianClientIntegrationTests.cs
@@ -313,6 +313,55 @@ public sealed class HistorianClientIntegrationTests
         Assert.Equal(host, status.ServerName);
     }
 
+    // The validator inside HistorianWcfTagClient now allows IntegratedSecurity=false WHEN
+    // explicit UserName + Password are provided (NTLM/Kerberos with non-current-user creds).
+    // It still rejects the no-credentials-at-all case since there's no way to authenticate
+    // against /Hist-Integrated.
+    [Fact]
+    public async Task GetTagMetadataAsync_NoAuthAndNoCredentials_Throws()
+    {
+        HistorianClient client = new(new HistorianClientOptions
+        {
+            Host = "localhost",
+            IntegratedSecurity = false,
+            UserName = string.Empty,
+            Password = string.Empty,
+        });
+        await Assert.ThrowsAsync<ProtocolEvidenceMissingException>(
+            () => client.GetTagMetadataAsync("anytag", CancellationToken.None));
+    }
+
+    [Fact]
+    public async Task GetTagMetadataAsync_ExplicitCredentials_AgainstLocalHistorian()
+    {
+        // Live verification of the explicit-creds tag-metadata path. Gated on
+        // HISTORIAN_USER + HISTORIAN_PASSWORD being set; skips cleanly otherwise. The path
+        // routes through WCF Windows transport security with Credentials.Windows.ClientCredential.
+        string? host = Environment.GetEnvironmentVariable("HISTORIAN_HOST");
+        string? testTag = Environment.GetEnvironmentVariable("HISTORIAN_TEST_TAG");
+        string? user = Environment.GetEnvironmentVariable("HISTORIAN_USER");
+        string? password = Environment.GetEnvironmentVariable("HISTORIAN_PASSWORD");
+        if (string.IsNullOrWhiteSpace(host) || string.IsNullOrWhiteSpace(testTag)
+            || string.IsNullOrWhiteSpace(user) || string.IsNullOrWhiteSpace(password)
+            || !OperatingSystem.IsWindows())
+        {
+            return;
+        }
+
+        HistorianClient client = new(new HistorianClientOptions
+        {
+            Host = host,
+            IntegratedSecurity = false,
+            UserName = user,
+            Password = password,
+        });
+
+        AVEVA.Historian.Client.Models.HistorianTagMetadata? metadata =
+            await client.GetTagMetadataAsync(testTag, CancellationToken.None);
+        Assert.NotNull(metadata);
+        Assert.Equal(testTag, metadata.Name);
+    }
+
     [Fact]
     public async Task GetTagMetadataAsync_ReturnsConfiguredTestTagMetadata()
     {