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Propagate CachedInputTokenCount in OpenTelemetry telemetry #7234

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Merged
stephentoub merged 4 commits into from
Jan 27, 2026
+9 −0
Merged

Propagate CachedInputTokenCount in OpenTelemetry telemetry #7234

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c7ba694
Initial plan
Copilot Jan 27, 2026
778fb82
Add cached input token count telemetry support for OpenTelemetryChatC…
Copilot Jan 27, 2026
04be7b4
Fix attribute name to gen_ai.usage.cache_read.input_tokens per semant…
Copilot Jan 27, 2026
35cce29
Remove TokenTypeCacheRead - only standard token types (input/output) …
Copilot Jan 27, 2026
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13 changes: 13 additions & 0 deletions src/Libraries/Microsoft.Extensions.AI/ChatCompletion/OpenTelemetryChatClient.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -528,6 +528,14 @@ private void TraceResponse(
AddMetricTags(ref tags, requestModelId, response);
_tokenUsageHistogram.Record((int)outputTokens, tags);
}

if (usage.CachedInputTokenCount is long cachedInputTokens)
{
TagList tags = default;
tags.Add(OpenTelemetryConsts.GenAI.Token.Type, OpenTelemetryConsts.TokenTypeCacheRead);
AddMetricTags(ref tags, requestModelId, response);
_tokenUsageHistogram.Record((int)cachedInputTokens, tags);
}
}

if (error is not null)
Expand Down Expand Up @@ -570,6 +578,11 @@ 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)
Expand Down
2 changes: 2 additions & 0 deletions src/Libraries/Microsoft.Extensions.AI/OpenTelemetryConsts.cs
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Expand Up @@ -24,6 +24,7 @@ internal static class OpenTelemetryConsts

public const string TokenTypeInput = "input";
public const string TokenTypeOutput = "output";
public const string TokenTypeCacheRead = "cache_read";
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public static class Error
{
Expand Down Expand Up @@ -138,6 +139,7 @@ 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";
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}
}

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3 changes: 3 additions & 0 deletions test/Libraries/Microsoft.Extensions.AI.Tests/ChatCompletion/OpenTelemetryChatClientTests.cs
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Expand Up @@ -44,6 +44,7 @@ public async Task ExpectedInformationLogged_Async(bool enableSensitiveData, bool
InputTokenCount = 10,
OutputTokenCount = 20,
TotalTokenCount = 42,
CachedInputTokenCount = 5,
},
AdditionalProperties = new()
{
Expand Down Expand Up @@ -84,6 +85,7 @@ async static IAsyncEnumerable<ChatResponseUpdate> CallbackAsync(
InputTokenCount = 10,
OutputTokenCount = 20,
TotalTokenCount = 42,
CachedInputTokenCount = 5,
})],
AdditionalProperties = new()
{
Expand Down Expand Up @@ -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"));

Expand Down
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