diff --git a/src/Plugins/BotSharp.Plugin.DeepSeekAI/Providers/Chat/ChatCompletionProvider.cs b/src/Plugins/BotSharp.Plugin.DeepSeekAI/Providers/Chat/ChatCompletionProvider.cs
index f81143e3..4f05ee8c 100644
--- a/src/Plugins/BotSharp.Plugin.DeepSeekAI/Providers/Chat/ChatCompletionProvider.cs
+++ b/src/Plugins/BotSharp.Plugin.DeepSeekAI/Providers/Chat/ChatCompletionProvider.cs
@@ -284,11 +284,21 @@ public class ChatCompletionProvider : IChatCompletion
 
             if (choice.FinishReason == ChatFinishReason.ToolCalls || choice.FinishReason == ChatFinishReason.FunctionCall)
             {
-                var meta = toolCalls.FirstOrDefault(x => !string.IsNullOrEmpty(x.FunctionName));
-                var functionName = meta?.FunctionName;
-                var toolCallId = meta?.ToolCallId;
-                var args = toolCalls.Where(x => x.FunctionArgumentsUpdate != null).Select(x => x.FunctionArgumentsUpdate.ToString()).ToList();
-                var functionArgument = string.Join(string.Empty, args);
+                // The model may emit several tool calls in one response. The OpenAI SDK streams each
+                // call's arguments as interleaved fragments per call index, so we must accumulate them
+                // PER CALL (grouped by index), not concatenate every fragment of every call together
+                // (that would corrupt arguments, e.g. get_node({"node_id": "10"}{"maxDepth": 2})).
+                var grouped = toolCalls
+                    .Where(x => !string.IsNullOrEmpty(x.FunctionName))
+                    .GroupBy(x => x.Index)
+                    .OrderBy(g => g.Key)
+                    .ToList();
+
+                var functionName = grouped.Count > 0 ? grouped[0].First().FunctionName : null;
+                var toolCallId = grouped.Count > 0 ? grouped[0].First().ToolCallId : null;
+                var functionArgument = grouped.Count > 0
+                    ? string.Concat(grouped[0].Where(x => x.FunctionArgumentsUpdate != null).Select(x => x.FunctionArgumentsUpdate.ToString()))
+                    : string.Empty;
 
 #if DEBUG
                 _logger.LogCritical($"Tool Call (id: {toolCallId}) => {functionName}({functionArgument})");
@@ -402,7 +412,20 @@ public class ChatCompletionProvider : IChatCompletion
 
     private static string? DecodePatchString(BinaryData data)
     {
+        if (data == null)
+        {
+            return null;
+        }
+
         var bytes = data.ToArray();
+
+        // JSON null literal (DeepSeek sends "reasoning_content": null in the final delta).
+        if (bytes.Length == 4 && bytes[0] == (byte)'n' && bytes[1] == (byte)'u' && bytes[2] == (byte)'l' && bytes[3] == (byte)'l')
+        {
+            return null;
+        }
+
+        // Quoted JSON string.
         if (bytes.Length >= 2 && bytes[0] == (byte)'"' && bytes[^1] == (byte)'"')
         {
             return System.Text.Encoding.UTF8.GetString(bytes, 1, bytes.Length - 2);