diff --git a/src/NATS.Server/NatsOptions.cs b/src/NATS.Server/NatsOptions.cs
index 8a9b56d..688a23f 100644
--- a/src/NATS.Server/NatsOptions.cs
+++ b/src/NATS.Server/NatsOptions.cs
@@ -71,6 +71,21 @@ public sealed class NatsOptions
     // Profiling (0 = disabled)
     public int ProfPort { get; set; }
 
+    // Extended options for Go parity
+    public string? ClientAdvertise { get; set; }
+    public bool TraceVerbose { get; set; }
+    public int MaxTracedMsgLen { get; set; }
+    public bool DisableSublistCache { get; set; }
+    public int ConnectErrorReports { get; set; } = 3600;
+    public int ReconnectErrorReports { get; set; } = 1;
+    public bool NoHeaderSupport { get; set; }
+    public int MaxClosedClients { get; set; } = 10_000;
+    public bool NoSystemAccount { get; set; }
+    public string? SystemAccount { get; set; }
+
+    // Tracks which fields were set via CLI flags (for reload precedence)
+    public HashSet<string> InCmdLine { get; } = [];
+
     // TLS
     public string? TlsCert { get; set; }
     public string? TlsKey { get; set; }
diff --git a/src/NATS.Server/NatsServer.cs b/src/NATS.Server/NatsServer.cs
index 02a0734..e6ac3dd 100644
--- a/src/NATS.Server/NatsServer.cs
+++ b/src/NATS.Server/NatsServer.cs
@@ -20,7 +20,6 @@ public sealed class NatsServer : IMessageRouter, ISubListAccess, IDisposable
     private readonly NatsOptions _options;
     private readonly ConcurrentDictionary<ulong, NatsClient> _clients = new();
     private readonly ConcurrentQueue<ClosedClient> _closedClients = new();
-    private const int MaxClosedClients = 10_000;
     private readonly ServerInfo _serverInfo;
     private readonly ILogger<NatsServer> _logger;
     private readonly ILoggerFactory _loggerFactory;
@@ -647,7 +646,7 @@ public sealed class NatsServer : IMessageRouter, ISubListAccess, IDisposable
         });
 
         // Cap closed clients list
-        while (_closedClients.Count > MaxClosedClients)
+        while (_closedClients.Count > _options.MaxClosedClients)
             _closedClients.TryDequeue(out _);
 
         var subList = client.Account?.SubList ?? _globalAccount.SubList;
diff --git a/tests/NATS.Server.Tests/NatsOptionsTests.cs b/tests/NATS.Server.Tests/NatsOptionsTests.cs
index 4e57769..e13d34c 100644
--- a/tests/NATS.Server.Tests/NatsOptionsTests.cs
+++ b/tests/NATS.Server.Tests/NatsOptionsTests.cs
@@ -14,4 +14,20 @@ public class NatsOptionsTests
         opts.LogSizeLimit.ShouldBe(0L);
         opts.Tags.ShouldBeNull();
     }
+
+    [Fact]
+    public void New_fields_have_correct_defaults()
+    {
+        var opts = new NatsOptions();
+        opts.ClientAdvertise.ShouldBeNull();
+        opts.TraceVerbose.ShouldBeFalse();
+        opts.MaxTracedMsgLen.ShouldBe(0);
+        opts.DisableSublistCache.ShouldBeFalse();
+        opts.ConnectErrorReports.ShouldBe(3600);
+        opts.ReconnectErrorReports.ShouldBe(1);
+        opts.NoHeaderSupport.ShouldBeFalse();
+        opts.MaxClosedClients.ShouldBe(10_000);
+        opts.NoSystemAccount.ShouldBeFalse();
+        opts.SystemAccount.ShouldBeNull();
+    }
 }