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Truncate gen_ai attributes to 256KB instead of exempting from truncation #48454

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Truncate gen_ai attributes to 256KB instead of exempting from truncation #48454

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Initial plan
Copilot Mar 17, 2026
095d05d
Truncate genai attributes to 256KB instead of exempting from truncation
Copilot Mar 17, 2026
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10 changes: 6 additions & 4 deletions ...monitor/opentelemetry/autoconfigure/implementation/builders/AbstractTelemetryBuilder.java
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Original file line number Diff line number Diff line change
Expand Up @@ -23,10 +23,11 @@ public abstract class AbstractTelemetryBuilder {

private static final int MAX_PROPERTY_KEY_LENGTH = 150;
private static final int MAX_PROPERTY_VALUE_LENGTH = 8192;
private static final int MAX_GENAI_PROPERTY_VALUE_LENGTH = 256 * 1024; // 256 KB

// gen_ai properties can contain large payloads (e.g. full conversation messages,
// tool definitions) that should not be truncated
private static final Set<String> TRUNCATION_EXEMPT_PROPERTY_KEYS = new HashSet<>(asList("gen_ai.input.messages",
// tool definitions) that are truncated at a higher limit (256 KB)
private static final Set<String> GENAI_PROPERTY_KEYS = new HashSet<>(asList("gen_ai.input.messages",
Comment on lines +26 to +30
"gen_ai.output.messages", "gen_ai.system_instructions", "gen_ai.tool.definitions", "gen_ai.tool.call.arguments",
"gen_ai.tool.call.result", "gen_ai.evaluation.explanation"));

Expand Down Expand Up @@ -89,8 +90,9 @@ public void addProperty(@Nullable String key, @Nullable String value) {
// TODO (trask) log
return;
}
if (TRUNCATION_EXEMPT_PROPERTY_KEYS.contains(key)) {
getProperties().put(key, value);
if (GENAI_PROPERTY_KEYS.contains(key)) {
getProperties().put(key,
TelemetryTruncation.truncatePropertyValue(value, MAX_GENAI_PROPERTY_VALUE_LENGTH, key));
} else {
getProperties().put(key, TelemetryTruncation.truncatePropertyValue(value, MAX_PROPERTY_VALUE_LENGTH, key));
Comment on lines +93 to 97
}
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23 changes: 22 additions & 1 deletion ...tor/opentelemetry/autoconfigure/implementation/builders/AbstractTelemetryBuilderTest.java
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Original file line number Diff line number Diff line change
Expand Up @@ -35,7 +35,28 @@ public void regularPropertyIsTruncatedAt8192() {
"gen_ai.tool.call.arguments",
"gen_ai.tool.call.result",
"gen_ai.evaluation.explanation" })
public void genAiPropertyIsNotTruncated(String key) {
public void genAiPropertyIsTruncatedAt256KB(String key) {
MessageTelemetryBuilder builder = MessageTelemetryBuilder.create();
int size256KB = 256 * 1024;
String longValue = repeat("a", size256KB + 10000);
builder.addProperty(key, longValue);

TelemetryItem item = builder.build();
Map<String, String> properties = getProperties(item);
assertEquals(size256KB, properties.get(key).length());
Comment on lines +40 to +46
}

@ParameterizedTest
@ValueSource(
strings = {
"gen_ai.input.messages",
"gen_ai.output.messages",
"gen_ai.system_instructions",
"gen_ai.tool.definitions",
"gen_ai.tool.call.arguments",
"gen_ai.tool.call.result",
"gen_ai.evaluation.explanation" })
public void genAiPropertyUnder256KBIsNotTruncated(String key) {
MessageTelemetryBuilder builder = MessageTelemetryBuilder.create();
String longValue = repeat("a", 50000);
builder.addProperty(key, longValue);
Expand Down
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