diff --git a/src/Braintrust.Sdk.Anthropic/InstrumentedMessageService.cs b/src/Braintrust.Sdk.Anthropic/InstrumentedMessageService.cs
index 76498e7..950a0d6 100644
--- a/src/Braintrust.Sdk.Anthropic/InstrumentedMessageService.cs
+++ b/src/Braintrust.Sdk.Anthropic/InstrumentedMessageService.cs
@@ -203,6 +203,7 @@ private static void TagActivity(
         double? timeToFirstToken = null)
     {
         activity.SetTag("provider", "anthropic");
+        activity.SetTag("braintrust.span_attributes", "{\"type\":\"llm\"}");
         activity.SetTag("gen_ai.request.model", request.Model.Raw());
         activity.SetTag("gen_ai.response.model", response.Model.Raw());
 
@@ -259,6 +260,7 @@ private static void TagStreamActivity(Activity activity, MessageCreateParams req
     {
         activity.SetTag("stream", true);
         activity.SetTag("provider", "anthropic");
+        activity.SetTag("braintrust.span_attributes", "{\"type\":\"llm\"}");
         activity.SetTag("gen_ai.request.model", request.Model.Raw());
 
         try
diff --git a/src/Braintrust.Sdk.OpenAI/InstrumentedChatClient.cs b/src/Braintrust.Sdk.OpenAI/InstrumentedChatClient.cs
index 1bace95..4733b94 100644
--- a/src/Braintrust.Sdk.OpenAI/InstrumentedChatClient.cs
+++ b/src/Braintrust.Sdk.OpenAI/InstrumentedChatClient.cs
@@ -141,6 +141,7 @@ private void TagActivity(
         IEnumerable<ChatMessage>? messages)
     {
         activity.SetTag("provider", "openai");
+        activity.SetTag("braintrust.span_attributes", "{\"type\":\"llm\"}");
 
         var requestRaw = activity.GetBaggageItem("braintrust.http.request");
         var responseRaw = activity.GetBaggageItem("braintrust.http.response");
diff --git a/tests/Braintrust.Sdk.Anthropic.Tests/BraintrustAnthropicTest.cs b/tests/Braintrust.Sdk.Anthropic.Tests/BraintrustAnthropicTest.cs
index 59bc399..97a0b89 100644
--- a/tests/Braintrust.Sdk.Anthropic.Tests/BraintrustAnthropicTest.cs
+++ b/tests/Braintrust.Sdk.Anthropic.Tests/BraintrustAnthropicTest.cs
@@ -170,6 +170,11 @@ public async Task MessageCreation_CapturesRequestAndResponse()
 
         var ttft = Convert.ToDouble(timeToFirstToken);
         Assert.True(ttft >= 0, "time_to_first_token should be non-negative");
+
+        // Verify span attributes type is set to "llm"
+        var spanAttributes = span.GetTagItem("braintrust.span_attributes") as string;
+        Assert.NotNull(spanAttributes);
+        Assert.Contains("\"type\":\"llm\"", spanAttributes);
     }
 
     [Fact]
diff --git a/tests/Braintrust.Sdk.OpenAI.Tests/BraintrustOpenAITest.cs b/tests/Braintrust.Sdk.OpenAI.Tests/BraintrustOpenAITest.cs
index 89bf7bc..d751ec6 100644
--- a/tests/Braintrust.Sdk.OpenAI.Tests/BraintrustOpenAITest.cs
+++ b/tests/Braintrust.Sdk.OpenAI.Tests/BraintrustOpenAITest.cs
@@ -182,6 +182,11 @@ public async Task ChatCompletion_CapturesRequestAndResponse()
         // Verify time_to_first_token is a non-negative number
         var ttft = Convert.ToDouble(timeToFirstToken);
         Assert.True(ttft >= 0, "time_to_first_token should be greater than or equal to 0");
+
+        // Verify span attributes type is set to "llm"
+        var spanAttributes = span.GetTagItem("braintrust.span_attributes") as string;
+        Assert.NotNull(spanAttributes);
+        Assert.Contains("\"type\":\"llm\"", spanAttributes);
     }
 
     [Fact]