fix: record the thinking budget and level on the call_llm telemetry span

core/src/main/java/com/google/adk/telemetry/README.md

@@ -37,7 +37,8 @@ Calls to Large Language Models (LLMs) are traced within a `call_llm` span. The
 *   Model name (`gen_ai.request.model`).
 *   Token usage (`gen_ai.usage.input_tokens`, `gen_ai.usage.output_tokens`).
 *   Configuration parameters (`gen_ai.request.top_p`,
-    `gen_ai.request.max_tokens`).
+    `gen_ai.request.max_tokens`, `gen_ai.request.reasoning.level`, and the
+    thinking budget as `gen_ai.usage.experimental.reasoning_tokens_limit`).
 *   Response finish reason (`gen_ai.response.finish_reasons`).
 
 ### Tool Calls and Responses

core/src/main/java/com/google/adk/telemetry/Tracing.java

@@ -30,6 +30,7 @@
 import com.google.genai.types.Content;
 import com.google.genai.types.FunctionResponse;
 import com.google.genai.types.Part;
+import com.google.genai.types.ThinkingConfig;
 import io.opentelemetry.api.GlobalOpenTelemetry;
 import io.opentelemetry.api.common.AttributeKey;
 import io.opentelemetry.api.trace.Span;
@@ -110,6 +111,8 @@ public class Tracing {
       AttributeKey.doubleKey("gen_ai.request.top_p");
   private static final AttributeKey<Long> GEN_AI_REQUEST_MAX_TOKENS =
       AttributeKey.longKey("gen_ai.request.max_tokens");
+  private static final AttributeKey<String> GEN_AI_REQUEST_REASONING_LEVEL =
+      AttributeKey.stringKey("gen_ai.request.reasoning.level");
   private static final AttributeKey<Long> GEN_AI_USAGE_INPUT_TOKENS =
       AttributeKey.longKey("gen_ai.usage.input_tokens");
   private static final AttributeKey<Long> GEN_AI_USAGE_OUTPUT_TOKENS =
@@ -118,6 +121,8 @@ public class Tracing {
       AttributeKey.longKey("gen_ai.usage.cache_read.input_tokens");
   private static final AttributeKey<Long> GEN_AI_USAGE_REASONING_OUTPUT_TOKENS =
       AttributeKey.longKey("gen_ai.usage.reasoning.output_tokens");
+  private static final AttributeKey<Long> GEN_AI_USAGE_REASONING_TOKENS_LIMIT =
+      AttributeKey.longKey("gen_ai.usage.experimental.reasoning_tokens_limit");
 
   private static final AttributeKey<String> ADK_TOOL_CALL_ARGS =
       AttributeKey.stringKey("gcp.vertex.agent.tool_call_args");
@@ -331,6 +336,19 @@ public static void traceCallLlm(
                   .ifPresent(
                       maxTokens ->
                           span.setAttribute(GEN_AI_REQUEST_MAX_TOKENS, maxTokens.longValue()));
+              config
+                  .thinkingConfig()
+                  .flatMap(ThinkingConfig::thinkingBudget)
+                  .ifPresent(
+                      budget ->
+                          span.setAttribute(
+                              GEN_AI_USAGE_REASONING_TOKENS_LIMIT, budget.longValue()));
+              // OTel wants the exact string sent to the provider, which toString() returns.
+              config
+                  .thinkingConfig()
+                  .flatMap(ThinkingConfig::thinkingLevel)
+                  .ifPresent(
+                      level -> span.setAttribute(GEN_AI_REQUEST_REASONING_LEVEL, level.toString()));
             });
     llmResponse
         .usageMetadata()

core/src/test/java/com/google/adk/telemetry/ContextPropagationTest.java

@@ -44,6 +44,7 @@
 import com.google.genai.types.GenerateContentConfig;
 import com.google.genai.types.GenerateContentResponseUsageMetadata;
 import com.google.genai.types.Part;
+import com.google.genai.types.ThinkingConfig;
 import io.opentelemetry.api.common.AttributeKey;
 import io.opentelemetry.api.common.Attributes;
 import io.opentelemetry.api.trace.Span;
@@ -533,6 +534,69 @@ public void testTraceCallLlm_withOnlyToolUsePromptTokens() {
     assertEquals(20L, (long) attrs.get(AttributeKey.longKey("gen_ai.usage.output_tokens")));
   }
 
+  @Test
+  public void testTraceCallLlm_withThinkingBudget() {
+    Span span = tracer.spanBuilder("test-thinking-budget").startSpan();
+    try (Scope scope = span.makeCurrent()) {
+      LlmRequest llmRequest =
+          LlmRequest.builder()
+              .model("gemini-pro")
+              .contents(ImmutableList.of(Content.fromParts(Part.fromText("hello"))))
+              .config(
+                  GenerateContentConfig.builder()
+                      .thinkingConfig(ThinkingConfig.builder().thinkingBudget(2048).build())
+                      .build())
+              .build();
+      Tracing.traceCallLlm(
+          span,
+          buildInvocationContext(),
+          "event-1",
+          llmRequest,
+          LlmResponse.builder().build(),
+          null);
+    } finally {
+      span.end();
+    }
+    List<SpanData> spans = openTelemetryRule.getSpans();
+    assertThat(spans).hasSize(1);
+    Attributes attrs = spans.get(0).getAttributes();
+    assertThat(attrs.get(AttributeKey.longKey("gen_ai.usage.experimental.reasoning_tokens_limit")))
+        .isEqualTo(2048L);
+    assertThat(attrs.get(AttributeKey.stringKey("gen_ai.request.reasoning.level"))).isNull();
+  }
+
+  @Test
+  public void testTraceCallLlm_withThinkingLevel_recordsValueSentToProvider() {
+    Span span = tracer.spanBuilder("test-thinking-level").startSpan();
+    try (Scope scope = span.makeCurrent()) {
+      LlmRequest llmRequest =
+          LlmRequest.builder()
+              .model("gemini-pro")
+              .contents(ImmutableList.of(Content.fromParts(Part.fromText("hello"))))
+              .config(
+                  GenerateContentConfig.builder()
+                      .thinkingConfig(ThinkingConfig.builder().thinkingLevel("low").build())
+                      .build())
+              .build();
+      Tracing.traceCallLlm(
+          span,
+          buildInvocationContext(),
+          "event-1",
+          llmRequest,
+          LlmResponse.builder().build(),
+          null);
+    } finally {
+      span.end();
+    }
+    List<SpanData> spans = openTelemetryRule.getSpans();
+    assertThat(spans).hasSize(1);
+    Attributes attrs = spans.get(0).getAttributes();
+    assertThat(attrs.get(AttributeKey.stringKey("gen_ai.request.reasoning.level")))
+        .isEqualTo("low");
+    assertThat(attrs.get(AttributeKey.longKey("gen_ai.usage.experimental.reasoning_tokens_limit")))
+        .isNull();
+  }
+
   @Test
   public void testTraceSendData() {
     Span span = tracer.spanBuilder("test").startSpan();