diff --git a/src/Google.Api.Gax.Grpc/ApiCall.cs b/src/Google.Api.Gax.Grpc/ApiCall.cs
index 0610fbfb..edb4a992 100644
--- a/src/Google.Api.Gax.Grpc/ApiCall.cs
+++ b/src/Google.Api.Gax.Grpc/ApiCall.cs
@@ -54,10 +54,7 @@ internal ApiCall(
         private readonly CallSettings _baseCallSettings;
 
         private T Call<T>(TRequest request, CallSettings perCallCallSettings, Func<CallSettings, T> fn)
-        {
-            CallSettings callSettings = CallSettings.Merge(_baseCallSettings, perCallCallSettings);
-            return fn(callSettings);
-        }
+            => fn(_baseCallSettings.MergedWith(perCallCallSettings));
 
         /// <summary>
         /// Performs an RPC call asynchronously.
@@ -80,23 +77,20 @@ public Task<TResponse> Async(TRequest request, CallSettings perCallCallSettings)
         public TResponse Sync(TRequest request, CallSettings perCallCallSettings) =>
             Call(request, perCallCallSettings, callSettings => _syncCall(request, callSettings));
 
-        internal ApiCall<TRequest, TResponse> WithUserAgent(string userAgent)
-        {
+        internal ApiCall<TRequest, TResponse> WithUserAgent(string userAgent) =>
             // TODO: Check that this is what we want. It allows call settings to remove our
             // user agent header. The caller can always do this manually anyway, of course, so
             // I'm tempted to leave it...
-            return new ApiCall<TRequest, TResponse>(
+            new ApiCall<TRequest, TResponse>(
                 _asyncCall,
                 _syncCall,
-                CallSettings.Merge(CallSettings.ForUserAgent(userAgent), _baseCallSettings));
-        }
+                CallSettings.FromHeader(UserAgentBuilder.HeaderName, userAgent)
+                    .MergedWith(_baseCallSettings));
 
-        internal ApiCall<TRequest, TResponse> WithRetry(IClock clock, IScheduler scheduler)
-        {
-            return new ApiCall<TRequest, TResponse>(
+        internal ApiCall<TRequest, TResponse> WithRetry(IClock clock, IScheduler scheduler) =>
+            new ApiCall<TRequest, TResponse>(
                 _asyncCall.WithRetry(clock, scheduler),
                 _syncCall.WithRetry(clock, scheduler),
                 _baseCallSettings);
-        }
     }
 }
diff --git a/src/Google.Api.Gax.Grpc/ApiCallRetryExtensions.cs b/src/Google.Api.Gax.Grpc/ApiCallRetryExtensions.cs
index a52bd2c2..87e7c805 100644
--- a/src/Google.Api.Gax.Grpc/ApiCallRetryExtensions.cs
+++ b/src/Google.Api.Gax.Grpc/ApiCallRetryExtensions.cs
@@ -34,8 +34,7 @@ internal static Func<TRequest, CallSettings, Task<TResponse>> WithRetry<TRequest
                     DateTime attemptDeadline = clock.GetCurrentDateTimeUtc() + callTimeout;
                     // Note: this handles a null total deadline due to "<" returning false if overallDeadline is null.
                     DateTime combinedDeadline = overallDeadline < attemptDeadline ? overallDeadline.Value : attemptDeadline;
-                    CallSettings attemptCallSettings = CallSettings.Merge
-                        (callSettings, CallSettings.FromCallTiming(CallTiming.FromDeadline(combinedDeadline)));
+                    CallSettings attemptCallSettings = callSettings.WithCallTiming(CallTiming.FromDeadline(combinedDeadline));
                     try
                     {
                         return await fn(request, attemptCallSettings);
@@ -74,8 +73,7 @@ internal static Func<TRequest, CallSettings, TResponse> WithRetry<TRequest, TRes
                     DateTime attemptDeadline = clock.GetCurrentDateTimeUtc() + callTimeout;
                     // Note: this handles a null total deadline due to "<" returning false if overallDeadline is null.
                     DateTime combinedDeadline = overallDeadline < attemptDeadline ? overallDeadline.Value : attemptDeadline;
-                    CallSettings attemptCallSettings = CallSettings.Merge
-                        (callSettings, CallSettings.FromCallTiming(CallTiming.FromDeadline(combinedDeadline)));
+                    CallSettings attemptCallSettings = callSettings.WithCallTiming(CallTiming.FromDeadline(combinedDeadline));
                     try
                     {
                         return fn(request, attemptCallSettings);
@@ -97,4 +95,3 @@ internal static Func<TRequest, CallSettings, TResponse> WithRetry<TRequest, TRes
 
     }
 }
-
diff --git a/src/Google.Api.Gax.Grpc/CallSettings.cs b/src/Google.Api.Gax.Grpc/CallSettings.cs
index 657bfd8a..f7fbc530 100644
--- a/src/Google.Api.Gax.Grpc/CallSettings.cs
+++ b/src/Google.Api.Gax.Grpc/CallSettings.cs
@@ -86,7 +86,7 @@ public CallSettings(
         /// <param name="original">Original settings. May be null.</param>
         /// <param name="overlaid">Settings to overlay. May be null.</param>
         /// <returns>A merged set of call settings.</returns>
-        public static CallSettings Merge(CallSettings original, CallSettings overlaid)
+        internal static CallSettings Merge(CallSettings original, CallSettings overlaid)
         {
             if (original == null)
             {
@@ -107,12 +107,6 @@ public static CallSettings Merge(CallSettings original, CallSettings overlaid)
                 overlaid.PropagationToken ?? original.PropagationToken);
         }
 
-        /// <summary>
-        /// Creates a <see cref="CallSettings"/> for the specified user agent.
-        /// </summary>
-        internal static CallSettings ForUserAgent(string userAgent) =>
-            FromHeaderMutation(metadata => metadata.Add(UserAgentBuilder.HeaderName, userAgent));
-
         /// <summary>
         /// Creates a <see cref="CallSettings"/> for the specified cancellation token.
         /// </summary>
diff --git a/src/Google.Api.Gax.Grpc/CallSettingsExtensions.cs b/src/Google.Api.Gax.Grpc/CallSettingsExtensions.cs
index 3d296859..eba2aff3 100644
--- a/src/Google.Api.Gax.Grpc/CallSettingsExtensions.cs
+++ b/src/Google.Api.Gax.Grpc/CallSettingsExtensions.cs
@@ -16,16 +16,14 @@ namespace Google.Api.Gax.Grpc
     public static class CallSettingsExtensions
     {
         /// <summary>
-        /// Shorthand for calling <see cref="CallSettings.Merge(CallSettings, CallSettings)"/>.
-        /// </summary>
-        /// <remarks>
         /// This method merges the settings in <paramref name="overlaid"/> with those in
         /// <paramref name="original"/>, with <paramref name="overlaid"/> taking priority.
         /// If both arguments are null, the result is null. If one argument is null,
         /// the other argument is returned. Otherwise, a new object is created with a property-wise
-        /// overlay. Any header mutations are combined, however: the mutation from the original is
+        /// overlay, where null values do not override non-null values.
+        /// Any header mutations are combined, however: the mutation from the original is
         /// performed, then the mutation in the overlay.
-        /// </remarks>
+        /// </summary>
         /// <param name="original">Original settings. May be null.</param>
         /// <param name="overlaid">Settings to overlay. May be null.</param>
         /// <returns>A merged set of call settings, or null if both parameters are null.</returns>
diff --git a/src/Google.Api.Gax.Grpc/ClientHelper.cs b/src/Google.Api.Gax.Grpc/ClientHelper.cs
index f307212e..c85175a5 100644
--- a/src/Google.Api.Gax.Grpc/ClientHelper.cs
+++ b/src/Google.Api.Gax.Grpc/ClientHelper.cs
@@ -62,7 +62,7 @@ public ApiCall<TRequest, TResponse> BuildApiCall<TRequest, TResponse>(
             where TRequest : class, IMessage<TRequest>
             where TResponse : class, IMessage<TResponse>
         {
-            CallSettings baseCallSettings = CallSettings.Merge(_clientCallSettings, perMethodCallSettings);
+            CallSettings baseCallSettings = _clientCallSettings.MergedWith(perMethodCallSettings);
             // These operations are applied in reverse order.
             // I.e. User-agent is added first, then retry is performed.
             return ApiCall.Create(asyncGrpcCall, syncGrpcCall, baseCallSettings, Clock)
diff --git a/src/Google.Api.Gax.Grpc/PageStreamingAsync.cs b/src/Google.Api.Gax.Grpc/PageStreamingAsync.cs
index 9b5b668c..ec72c0f1 100644
--- a/src/Google.Api.Gax.Grpc/PageStreamingAsync.cs
+++ b/src/Google.Api.Gax.Grpc/PageStreamingAsync.cs
@@ -107,7 +107,7 @@ public async Task<bool> MoveNext(CancellationToken cancellationToken)
                 CallSettings effectiveCallSettings = _callSettings;
                 if (cancellationToken != default(CancellationToken))
                 {
-                    effectiveCallSettings = CallSettings.Merge(_callSettings, CallSettings.FromCancellationToken(cancellationToken));
+                    effectiveCallSettings = _callSettings.WithCancellationToken(cancellationToken);
                 }
                 Current = await _apiCall.Async(_request, effectiveCallSettings);
                 var nextPageToken = Current.NextPageToken;