diff --git a/src/Libraries/Microsoft.Extensions.AI/ChatCompletion/OpenTelemetryChatClient.cs b/src/Libraries/Microsoft.Extensions.AI/ChatCompletion/OpenTelemetryChatClient.cs
index 264832508ae..bbe684bb7bd 100644
--- a/src/Libraries/Microsoft.Extensions.AI/ChatCompletion/OpenTelemetryChatClient.cs
+++ b/src/Libraries/Microsoft.Extensions.AI/ChatCompletion/OpenTelemetryChatClient.cs
@@ -570,6 +570,11 @@ private void TraceResponse(
                     _ = activity.AddTag(OpenTelemetryConsts.GenAI.Usage.OutputTokens, (int)outputTokens);
                 }
 
+                if (response.Usage?.CachedInputTokenCount is long cachedInputTokens)
+                {
+                    _ = activity.AddTag(OpenTelemetryConsts.GenAI.Usage.CacheReadInputTokens, (int)cachedInputTokens);
+                }
+
                 // Log all additional response properties as raw values on the span.
                 // Since AdditionalProperties has undefined meaning, we treat it as potentially sensitive data.
                 if (EnableSensitiveData && response.AdditionalProperties is { } props)
diff --git a/src/Libraries/Microsoft.Extensions.AI/OpenTelemetryConsts.cs b/src/Libraries/Microsoft.Extensions.AI/OpenTelemetryConsts.cs
index fa7e36333ce..d2fefa64002 100644
--- a/src/Libraries/Microsoft.Extensions.AI/OpenTelemetryConsts.cs
+++ b/src/Libraries/Microsoft.Extensions.AI/OpenTelemetryConsts.cs
@@ -138,6 +138,7 @@ public static class Usage
         {
             public const string InputTokens = "gen_ai.usage.input_tokens";
             public const string OutputTokens = "gen_ai.usage.output_tokens";
+            public const string CacheReadInputTokens = "gen_ai.usage.cache_read.input_tokens";
         }
     }
 
diff --git a/test/Libraries/Microsoft.Extensions.AI.Tests/ChatCompletion/OpenTelemetryChatClientTests.cs b/test/Libraries/Microsoft.Extensions.AI.Tests/ChatCompletion/OpenTelemetryChatClientTests.cs
index e7206b05ff5..f67c62f0ed4 100644
--- a/test/Libraries/Microsoft.Extensions.AI.Tests/ChatCompletion/OpenTelemetryChatClientTests.cs
+++ b/test/Libraries/Microsoft.Extensions.AI.Tests/ChatCompletion/OpenTelemetryChatClientTests.cs
@@ -44,6 +44,7 @@ public async Task ExpectedInformationLogged_Async(bool enableSensitiveData, bool
                         InputTokenCount = 10,
                         OutputTokenCount = 20,
                         TotalTokenCount = 42,
+                        CachedInputTokenCount = 5,
                     },
                     AdditionalProperties = new()
                     {
@@ -84,6 +85,7 @@ async static IAsyncEnumerable<ChatResponseUpdate> CallbackAsync(
                     InputTokenCount = 10,
                     OutputTokenCount = 20,
                     TotalTokenCount = 42,
+                    CachedInputTokenCount = 5,
                 })],
                 AdditionalProperties = new()
                 {
@@ -180,6 +182,7 @@ async static IAsyncEnumerable<ChatResponseUpdate> CallbackAsync(
         Assert.Equal("""["stop"]""", activity.GetTagItem("gen_ai.response.finish_reasons"));
         Assert.Equal(10, activity.GetTagItem("gen_ai.usage.input_tokens"));
         Assert.Equal(20, activity.GetTagItem("gen_ai.usage.output_tokens"));
+        Assert.Equal(5, activity.GetTagItem("gen_ai.usage.cache_read.input_tokens"));
         Assert.Equal(enableSensitiveData ? "abcdefgh" : null, activity.GetTagItem("system_fingerprint"));
         Assert.Equal(enableSensitiveData ? "value2" : null, activity.GetTagItem("AndSomethingElse"));