diff --git a/csharp/src/Ice/InputStream.cs b/csharp/src/Ice/InputStream.cs
index 13b0eb686c0..5b11997daf0 100644
--- a/csharp/src/Ice/InputStream.cs
+++ b/csharp/src/Ice/InputStream.cs
@@ -2,9 +2,9 @@
 
 #nullable enable
 
+using Ice.Internal;
 using System.Diagnostics;
 using System.Globalization;
-
 using Protocol = Ice.Internal.Protocol;
 
 namespace Ice;
@@ -26,89 +26,60 @@ public class InputStream
     /// Initializes a new instance of the <see cref="InputStream" /> class. This constructor uses the communicator's
     /// default encoding version.
     /// </summary>
-    /// <param name="communicator">The communicator to use when initializing the stream.</param>
+    /// <param name="communicator">The communicator to use when unmarshaling classes, exceptions and proxies.</param>
     /// <param name="data">The byte array containing encoded Slice types.</param>
     public InputStream(Communicator communicator, byte[] data)
+        : this(
+            communicator.instance,
+            communicator.instance.defaultsAndOverrides().defaultEncoding,
+            new Internal.Buffer(data))
     {
-        initialize(communicator);
-        _buf = new Ice.Internal.Buffer(data);
     }
 
     /// <summary>
-    /// Initializes a new instance of the <see cref="InputStream" /> class. This constructor uses the given encoding
-    /// version.
+    /// Initializes a new instance of the <see cref="InputStream" /> class.
     /// </summary>
-    /// <param name="communicator">The communicator to use when initializing the stream.</param>
+    /// <param name="communicator">The communicator to use when unmarshaling classes, exceptions and proxies.</param>
     /// <param name="encoding">The desired encoding version.</param>
     /// <param name="data">The byte array containing encoded Slice types.</param>
     public InputStream(Communicator communicator, EncodingVersion encoding, byte[] data)
+        : this(communicator.instance, encoding, new Internal.Buffer(data))
     {
-        initialize(communicator, encoding);
-        _buf = new Ice.Internal.Buffer(data);
-    }
-
-    public InputStream(Ice.Internal.Instance instance, EncodingVersion encoding)
-    {
-        initialize(instance, encoding);
-        _buf = new Ice.Internal.Buffer();
-    }
-
-    public InputStream(Ice.Internal.Instance instance, EncodingVersion encoding, Ice.Internal.Buffer buf, bool adopt)
-    {
-        initialize(instance, encoding);
-        _buf = new Ice.Internal.Buffer(buf, adopt);
     }
 
     /// <summary>
-    /// Initializes the stream to use the communicator's default encoding version.
+    /// Initializes a new instance of the <see cref="InputStream" /> class with an empty buffer.
     /// </summary>
-    /// <param name="communicator">The communicator to use when initializing the stream.</param>
-    public void initialize(Communicator communicator)
+    internal InputStream(Instance instance, EncodingVersion encoding)
+        : this(instance, encoding, new Internal.Buffer())
     {
-        Debug.Assert(communicator != null);
-        Ice.Internal.Instance instance = communicator.instance;
-        initialize(instance, instance.defaultsAndOverrides().defaultEncoding);
     }
 
     /// <summary>
-    /// Initializes the stream to use the given communicator and encoding version.
+    /// Initializes a new instance of the <see cref="InputStream" /> class while adopting or borrowing the underlying
+    /// buffer.
     /// </summary>
-    /// <param name="communicator">The communicator to use when initializing the stream.</param>
-    /// <param name="encoding">The desired encoding version.</param>
-    public void initialize(Communicator communicator, EncodingVersion encoding)
+    internal InputStream(Instance instance, EncodingVersion encoding, Internal.Buffer buf, bool adopt)
+        : this(instance, encoding, new Internal.Buffer(buf, adopt))
     {
-        Debug.Assert(communicator != null);
-        Ice.Internal.Instance instance = communicator.instance;
-        initialize(instance, encoding);
     }
 
-    private void initialize(Ice.Internal.Instance instance, EncodingVersion encoding)
+    /// <summary>
+    /// Initializes a new instance of the <see cref="InputStream" /> class. All other constructors delegate to this
+    /// constructor.
+    /// </summary>
+    private InputStream(Instance instance, EncodingVersion encoding, Internal.Buffer buf)
     {
-        initialize(encoding);
-
+        _encoding = encoding;
         _instance = instance;
-        _traceSlicing = _instance.traceLevels().slicing > 0;
+        _buf = buf;
         _classGraphDepthMax = _instance.classGraphDepthMax();
-        _valueFactoryManager = _instance.initializationData().valueFactoryManager;
-        _logger = _instance.initializationData().logger;
-    }
-
-    private void initialize(EncodingVersion encoding)
-    {
-        _instance = null;
-        _encoding = encoding;
-        _encapsStack = null;
-        _encapsCache = null;
-        _traceSlicing = false;
-        _classGraphDepthMax = 0x7fffffff;
-        _closure = null;
-        _startSeq = -1;
-        _minSeqSize = 0;
+        // The communicator initialization always sets a non-null ValueFactoryManager in its initialization data.
+        _valueFactoryManager = _instance.initializationData().valueFactoryManager!;
     }
 
     /// <summary>
-    /// Resets this stream. This method allows the stream to be reused, to avoid creating
-    /// unnecessary garbage.
+    /// Resets this stream. This method allows the stream to be reused, to avoid creating unnecessary garbage.
     /// </summary>
     public void reset()
     {
@@ -133,75 +104,7 @@ public void clear()
         _startSeq = -1;
     }
 
-    /// <summary>
-    /// Sets the value factory manager to use when marshaling value instances. If the stream
-    /// was initialized with a communicator, the communicator's value factory manager will
-    /// be used by default.
-    /// </summary>
-    /// <param name="vfm">The value factory manager.</param>
-    public void setValueFactoryManager(ValueFactoryManager vfm)
-    {
-        _valueFactoryManager = vfm;
-    }
-
-    /// <summary>
-    /// Sets the logger to use when logging trace messages. If the stream
-    /// was initialized with a communicator, the communicator's logger will
-    /// be used by default.
-    /// </summary>
-    /// <param name="logger">The logger to use for logging trace messages.</param>
-    public void setLogger(Logger logger)
-    {
-        _logger = logger;
-    }
-
-    /// <summary>
-    /// Determines whether the stream logs messages about slicing instances of Slice values.
-    /// </summary>
-    /// <param name="b">True to enable logging, false to disable logging.</param>
-    public void setTraceSlicing(bool b)
-    {
-        _traceSlicing = b;
-    }
-
-    /// <summary>
-    /// Set the maximum depth allowed for graph of Slice class instances.
-    /// </summary>
-    /// <param name="classGraphDepthMax">The maximum depth.</param>
-    public void setClassGraphDepthMax(int classGraphDepthMax)
-    {
-        if (classGraphDepthMax < 1)
-        {
-            _classGraphDepthMax = 0x7fffffff;
-        }
-        else
-        {
-            _classGraphDepthMax = classGraphDepthMax;
-        }
-    }
-
-    /// <summary>
-    /// Retrieves the closure object associated with this stream.
-    /// </summary>
-    /// <returns>The closure object.</returns>
-    public object? getClosure()
-    {
-        return _closure;
-    }
-
-    /// <summary>
-    /// Associates a closure object with this stream.
-    /// </summary>
-    /// <param name="p">The new closure object.</param>
-    /// <returns>The previous closure object, or null.</returns>
-    public object? setClosure(object p)
-    {
-        object? prev = _closure;
-        _closure = p;
-        return prev;
-    }
-
-    internal Ice.Internal.Instance? instance() => _instance;
+    internal Instance instance() => _instance;
 
     /// <summary>
     /// Swaps the contents of one stream with another.
@@ -210,8 +113,11 @@ public void setClassGraphDepthMax(int classGraphDepthMax)
     public void swap(InputStream other)
     {
         Debug.Assert(_instance == other._instance);
+        // _valueFactoryManager and _classGraphDepthMax come from _instance.
+        Debug.Assert(_valueFactoryManager == other._valueFactoryManager);
+        Debug.Assert(_classGraphDepthMax == other._classGraphDepthMax);
 
-        Ice.Internal.Buffer tmpBuf = other._buf;
+        Internal.Buffer tmpBuf = other._buf;
         other._buf = _buf;
         _buf = tmpBuf;
 
@@ -219,18 +125,6 @@ public void swap(InputStream other)
         other._encoding = _encoding;
         _encoding = tmpEncoding;
 
-        bool tmpTraceSlicing = other._traceSlicing;
-        other._traceSlicing = _traceSlicing;
-        _traceSlicing = tmpTraceSlicing;
-
-        object? tmpClosure = other._closure;
-        other._closure = _closure;
-        _closure = tmpClosure;
-
-        int tmpClassGraphDepthMax = other._classGraphDepthMax;
-        other._classGraphDepthMax = _classGraphDepthMax;
-        _classGraphDepthMax = tmpClassGraphDepthMax;
-
         //
         // Swap is never called for InputStreams that have encapsulations being read. However,
         // encapsulations might still be set in case un-marshaling failed. We just
@@ -246,14 +140,6 @@ public void swap(InputStream other)
         int tmpMinSeqSize = other._minSeqSize;
         other._minSeqSize = _minSeqSize;
         _minSeqSize = tmpMinSeqSize;
-
-        ValueFactoryManager? tmpVfm = other._valueFactoryManager;
-        other._valueFactoryManager = _valueFactoryManager;
-        _valueFactoryManager = tmpVfm;
-
-        Logger? tmpLogger = other._logger;
-        other._logger = _logger;
-        _logger = tmpLogger;
     }
 
     private void resetEncapsulation()
@@ -271,10 +157,7 @@ public void resize(int sz)
         _buf.b.position(sz);
     }
 
-    public Ice.Internal.Buffer getBuffer()
-    {
-        return _buf;
-    }
+    internal Internal.Buffer getBuffer() => _buf;
 
     /// <summary>
     /// Marks the start of a class instance.
@@ -2144,11 +2027,6 @@ public void readStringSeq(int tag, out bool isset, out string[]? v)
     /// <returns>The extracted proxy.</returns>
     public ObjectPrx? readProxy()
     {
-        if (_instance is null)
-        {
-            throw new MarshalException("cannot unmarshal a proxy without a communicator");
-        }
-
         var ident = new Identity(this);
         if (ident.name.Length == 0)
         {
@@ -2464,7 +2342,7 @@ private bool skipOptionals()
     {
         try
         {
-            return (UserException?)_instance!.getActivator().CreateInstance(id);
+            return (UserException?)_instance.getActivator().CreateInstance(id);
         }
         catch (System.Exception ex)
         {
@@ -2472,9 +2350,8 @@ private bool skipOptionals()
         }
     }
 
-    private Ice.Internal.Instance? _instance;
-    private Ice.Internal.Buffer _buf;
-    private object? _closure;
+    private readonly Instance _instance;
+    private Internal.Buffer _buf;
     private byte[]? _stringBytes; // Reusable array for reading strings.
 
     private enum SliceType
@@ -2498,7 +2375,7 @@ public PatchEntry(System.Action<Value> cb, int classGraphDepth)
             public int classGraphDepth;
         }
 
-        internal EncapsDecoder(InputStream stream, Encaps encaps, int classGraphDepthMax, ValueFactoryManager? f)
+        internal EncapsDecoder(InputStream stream, Encaps encaps, int classGraphDepthMax, ValueFactoryManager f)
         {
             _stream = stream;
             _encaps = encaps;
@@ -2561,7 +2438,7 @@ protected string readTypeId(bool isIndex)
             //
             // Try to find a factory registered for the specific type.
             //
-            var userFactory = _valueFactoryManager!.find(typeId);
+            var userFactory = _valueFactoryManager.find(typeId);
             Value? v = null;
             if (userFactory != null)
             {
@@ -2574,7 +2451,7 @@ protected string readTypeId(bool isIndex)
             //
             if (v is null)
             {
-                userFactory = _valueFactoryManager!.find("");
+                userFactory = _valueFactoryManager.find("");
                 if (userFactory != null)
                 {
                     v = userFactory(typeId);
@@ -2588,7 +2465,7 @@ protected string readTypeId(bool isIndex)
             {
                 try
                 {
-                    v = (Value?)_stream._instance!.getActivator().CreateInstance(typeId);
+                    v = (Value?)_stream._instance.getActivator().CreateInstance(typeId);
                 }
                 catch (System.Exception ex)
                 {
@@ -2727,8 +2604,7 @@ protected void unmarshal(int index, Value v)
         protected readonly int _classGraphDepthMax;
         protected int _classGraphDepth;
 
-        // It's null when _instance is null. We can't decode classes/exceptions/proxies in this case.
-        protected ValueFactoryManager? _valueFactoryManager;
+        protected ValueFactoryManager _valueFactoryManager;
 
         //
         // Encapsulation attributes for object unmarshaling.
@@ -2742,7 +2618,7 @@ protected void unmarshal(int index, Value v)
 
     private sealed class EncapsDecoder10 : EncapsDecoder
     {
-        internal EncapsDecoder10(InputStream stream, Encaps encaps, int classGraphDepthMax, ValueFactoryManager? f)
+        internal EncapsDecoder10(InputStream stream, Encaps encaps, int classGraphDepthMax, ValueFactoryManager f)
             : base(stream, encaps, classGraphDepthMax, f)
         {
             _sliceType = SliceType.NoSlice;
@@ -3047,7 +2923,7 @@ private void readInstance()
 
     private sealed class EncapsDecoder11 : EncapsDecoder
     {
-        internal EncapsDecoder11(InputStream stream, Encaps encaps, int classGraphDepthMax, ValueFactoryManager? f)
+        internal EncapsDecoder11(InputStream stream, Encaps encaps, int classGraphDepthMax, ValueFactoryManager f)
             : base(stream, encaps, classGraphDepthMax, f)
         {
             _current = null;
@@ -3656,14 +3532,12 @@ private void initEncaps()
         }
     }
 
-    private bool _traceSlicing;
-    private int _classGraphDepthMax;
+    private readonly int _classGraphDepthMax;
 
-    private int _startSeq;
+    private int _startSeq = -1;
     private int _minSeqSize;
 
-    private ValueFactoryManager? _valueFactoryManager;
-    private Logger? _logger;
+    private readonly ValueFactoryManager _valueFactoryManager;
 
     private const string endOfBufferMessage = "Attempting to unmarshal past the end of the buffer.";
 }
diff --git a/csharp/src/Ice/OutputStream.cs b/csharp/src/Ice/OutputStream.cs
index a74daac2e74..ab58f518b83 100644
--- a/csharp/src/Ice/OutputStream.cs
+++ b/csharp/src/Ice/OutputStream.cs
@@ -69,27 +69,6 @@ public void clear()
         }
     }
 
-    /// <summary>
-    /// Retrieves the closure object associated with this stream.
-    /// </summary>
-    /// <returns>The closure object.</returns>
-    public object? getClosure()
-    {
-        return _closure;
-    }
-
-    /// <summary>
-    /// Associates a closure object with this stream.
-    /// </summary>
-    /// <param name="p">The new closure object.</param>
-    /// <returns>The previous closure object, or null.</returns>
-    public object? setClosure(object p)
-    {
-        object? prev = _closure;
-        _closure = p;
-        return prev;
-    }
-
     /// <summary>
     /// Indicates that the marshaling of a request or reply is finished.
     /// </summary>
@@ -116,10 +95,6 @@ public void swap(OutputStream other)
         other._encoding = _encoding;
         _encoding = tmpEncoding;
 
-        object? tmpClosure = other._closure;
-        other._closure = _closure;
-        _closure = tmpClosure;
-
         //
         // Swap is never called for streams that have encapsulations being written. However,
         // encapsulations might still be set in case marshaling failed. We just
@@ -1767,8 +1742,6 @@ internal Ice.Internal.Buffer getBuffer()
 
     private Ice.Internal.Buffer _buf;
 
-    private object? _closure;
-
     private readonly FormatType _format;
 
     private enum SliceType