diff --git a/genai_otel_conformance/specs.py b/genai_otel_conformance/specs.py
index 6e0e9d2b..1dc6ad42 100644
--- a/genai_otel_conformance/specs.py
+++ b/genai_otel_conformance/specs.py
@@ -64,6 +64,7 @@ def attrs_for_requirement_level(self, level: RequirementLevel) -> tuple[str, ...
     "gen_ai.usage.cache_read.input_tokens",
     "gen_ai.usage.input_tokens",
     "gen_ai.usage.output_tokens",
+    "gen_ai.usage.reasoning.output_tokens",
 ]
 _INFERENCE_OPT_IN = [
     "gen_ai.input.messages",
diff --git a/tests/dotnet/azure-openai/Program.cs b/tests/dotnet/azure-openai/Program.cs
index d6987cb1..6dc8ce4c 100644
--- a/tests/dotnet/azure-openai/Program.cs
+++ b/tests/dotnet/azure-openai/Program.cs
@@ -167,6 +167,8 @@ static async Task RunPrototype()
             {
                 activity?.SetTag("gen_ai.usage.input_tokens", completion.Usage.InputTokenCount);
                 activity?.SetTag("gen_ai.usage.output_tokens", completion.Usage.OutputTokenCount);
+                if (completion.Usage.OutputTokenDetails?.ReasoningTokenCount > 0)
+                    activity?.SetTag("gen_ai.usage.reasoning.output_tokens", completion.Usage.OutputTokenDetails.ReasoningTokenCount);
             }
 
             var content = completion.Content[0].Text;
@@ -191,6 +193,7 @@ static async Task RunPrototype()
                 ["gen_ai.response.finish_reasons"] = new[] { completion.FinishReason.ToString() },
                 ["gen_ai.usage.input_tokens"] = completion.Usage?.InputTokenCount,
                 ["gen_ai.usage.output_tokens"] = completion.Usage?.OutputTokenCount,
+                ["gen_ai.usage.reasoning.output_tokens"] = completion.Usage?.OutputTokenDetails?.ReasoningTokenCount > 0 ? completion.Usage.OutputTokenDetails.ReasoningTokenCount : null,
                 ["gen_ai.input.messages"] = inputMessagesJson,
                 ["gen_ai.output.messages"] = outputMessagesJson,
                 ["server.address"] = endpoint.Host,
@@ -228,6 +231,8 @@ static async Task RunPrototype()
                 {
                     activity?.SetTag("gen_ai.usage.input_tokens", update.Usage.InputTokenCount);
                     activity?.SetTag("gen_ai.usage.output_tokens", update.Usage.OutputTokenCount);
+                    if (update.Usage.OutputTokenDetails?.ReasoningTokenCount > 0)
+                        activity?.SetTag("gen_ai.usage.reasoning.output_tokens", update.Usage.OutputTokenDetails.ReasoningTokenCount);
                 }
             }
 
@@ -301,6 +306,8 @@ static async Task RunPrototype()
             {
                 activity?.SetTag("gen_ai.usage.input_tokens", completion.Usage.InputTokenCount);
                 activity?.SetTag("gen_ai.usage.output_tokens", completion.Usage.OutputTokenCount);
+                if (completion.Usage.OutputTokenDetails?.ReasoningTokenCount > 0)
+                    activity?.SetTag("gen_ai.usage.reasoning.output_tokens", completion.Usage.OutputTokenDetails.ReasoningTokenCount);
             }
 
             if (completion.ToolCalls.Count > 0)
diff --git a/tests/dotnet/azure-openai/data-prototype.json b/tests/dotnet/azure-openai/data-prototype.json
index 8e5e0c03..ee8863e3 100644
--- a/tests/dotnet/azure-openai/data-prototype.json
+++ b/tests/dotnet/azure-openai/data-prototype.json
@@ -10,6 +10,7 @@
       "gen_ai.tool.definitions",
       "gen_ai.usage.input_tokens",
       "gen_ai.usage.output_tokens",
+      "gen_ai.usage.reasoning.output_tokens",
       "server.address",
       "server.port"
     ]
diff --git a/tests/dotnet/extensions-ai/Program.cs b/tests/dotnet/extensions-ai/Program.cs
index 6e5b030d..19290f94 100644
--- a/tests/dotnet/extensions-ai/Program.cs
+++ b/tests/dotnet/extensions-ai/Program.cs
@@ -166,6 +166,8 @@ static async Task RunPrototype()
             {
                 activity?.SetTag("gen_ai.usage.input_tokens", completion.Usage.InputTokenCount);
                 activity?.SetTag("gen_ai.usage.output_tokens", completion.Usage.OutputTokenCount);
+                if (completion.Usage.OutputTokenDetails?.ReasoningTokenCount > 0)
+                    activity?.SetTag("gen_ai.usage.reasoning.output_tokens", completion.Usage.OutputTokenDetails.ReasoningTokenCount);
             }
 
             var content = completion.Content[0].Text;
@@ -190,6 +192,7 @@ static async Task RunPrototype()
                 ["gen_ai.response.finish_reasons"] = new[] { completion.FinishReason.ToString() },
                 ["gen_ai.usage.input_tokens"] = completion.Usage?.InputTokenCount,
                 ["gen_ai.usage.output_tokens"] = completion.Usage?.OutputTokenCount,
+                ["gen_ai.usage.reasoning.output_tokens"] = completion.Usage?.OutputTokenDetails?.ReasoningTokenCount > 0 ? completion.Usage.OutputTokenDetails.ReasoningTokenCount : null,
                 ["gen_ai.input.messages"] = inputMessagesJson,
                 ["gen_ai.output.messages"] = outputMessagesJson,
                 ["server.address"] = endpoint.Host,
@@ -227,6 +230,8 @@ static async Task RunPrototype()
                 {
                     activity?.SetTag("gen_ai.usage.input_tokens", update.Usage.InputTokenCount);
                     activity?.SetTag("gen_ai.usage.output_tokens", update.Usage.OutputTokenCount);
+                    if (update.Usage.OutputTokenDetails?.ReasoningTokenCount > 0)
+                        activity?.SetTag("gen_ai.usage.reasoning.output_tokens", update.Usage.OutputTokenDetails.ReasoningTokenCount);
                 }
             }
 
@@ -300,6 +305,8 @@ static async Task RunPrototype()
             {
                 activity?.SetTag("gen_ai.usage.input_tokens", completion.Usage.InputTokenCount);
                 activity?.SetTag("gen_ai.usage.output_tokens", completion.Usage.OutputTokenCount);
+                if (completion.Usage.OutputTokenDetails?.ReasoningTokenCount > 0)
+                    activity?.SetTag("gen_ai.usage.reasoning.output_tokens", completion.Usage.OutputTokenDetails.ReasoningTokenCount);
             }
 
             if (completion.ToolCalls.Count > 0)
diff --git a/tests/dotnet/extensions-ai/data-prototype.json b/tests/dotnet/extensions-ai/data-prototype.json
index 8e5e0c03..ee8863e3 100644
--- a/tests/dotnet/extensions-ai/data-prototype.json
+++ b/tests/dotnet/extensions-ai/data-prototype.json
@@ -10,6 +10,7 @@
       "gen_ai.tool.definitions",
       "gen_ai.usage.input_tokens",
       "gen_ai.usage.output_tokens",
+      "gen_ai.usage.reasoning.output_tokens",
       "server.address",
       "server.port"
     ]
diff --git a/tests/dotnet/semantic-kernel/Program.cs b/tests/dotnet/semantic-kernel/Program.cs
index 7b938777..2a1d1881 100644
--- a/tests/dotnet/semantic-kernel/Program.cs
+++ b/tests/dotnet/semantic-kernel/Program.cs
@@ -193,6 +193,7 @@ static async Task RunPrototype()
             string finishReason = null;
             int? inputTokens = null;
             int? outputTokens = null;
+            int? reasoningTokens = null;
             if (metadata != null)
             {
                 if (metadata.TryGetValue("Id", out var id) && id != null)
@@ -213,6 +214,11 @@ static async Task RunPrototype()
                     outputTokens = usage.OutputTokenCount;
                     activity?.SetTag("gen_ai.usage.input_tokens", inputTokens);
                     activity?.SetTag("gen_ai.usage.output_tokens", outputTokens);
+                    if (usage.OutputTokenDetails?.ReasoningTokenCount > 0)
+                    {
+                        reasoningTokens = usage.OutputTokenDetails.ReasoningTokenCount;
+                        activity?.SetTag("gen_ai.usage.reasoning.output_tokens", reasoningTokens);
+                    }
                 }
             }
 
@@ -236,6 +242,7 @@ static async Task RunPrototype()
                 ["gen_ai.response.finish_reasons"] = finishReason != null ? new[] { finishReason } : null,
                 ["gen_ai.usage.input_tokens"] = inputTokens,
                 ["gen_ai.usage.output_tokens"] = outputTokens,
+                ["gen_ai.usage.reasoning.output_tokens"] = reasoningTokens,
                 ["gen_ai.input.messages"] = inputMessagesJson,
                 ["gen_ai.output.messages"] = outputMessagesJson,
                 ["server.address"] = endpoint.Host,
@@ -279,6 +286,8 @@ static async Task RunPrototype()
                     {
                         activity?.SetTag("gen_ai.usage.input_tokens", usage.InputTokenCount);
                         activity?.SetTag("gen_ai.usage.output_tokens", usage.OutputTokenCount);
+                        if (usage.OutputTokenDetails?.ReasoningTokenCount > 0)
+                            activity?.SetTag("gen_ai.usage.reasoning.output_tokens", usage.OutputTokenDetails.ReasoningTokenCount);
                     }
                 }
             }
@@ -347,6 +356,8 @@ static async Task RunPrototype()
                 {
                     activity?.SetTag("gen_ai.usage.input_tokens", usage.InputTokenCount);
                     activity?.SetTag("gen_ai.usage.output_tokens", usage.OutputTokenCount);
+                    if (usage.OutputTokenDetails?.ReasoningTokenCount > 0)
+                        activity?.SetTag("gen_ai.usage.reasoning.output_tokens", usage.OutputTokenDetails.ReasoningTokenCount);
                 }
             }
 
diff --git a/tests/dotnet/semantic-kernel/data-prototype.json b/tests/dotnet/semantic-kernel/data-prototype.json
index a26e5d2f..f42e38ac 100644
--- a/tests/dotnet/semantic-kernel/data-prototype.json
+++ b/tests/dotnet/semantic-kernel/data-prototype.json
@@ -10,6 +10,7 @@
       "gen_ai.tool.definitions",
       "gen_ai.usage.input_tokens",
       "gen_ai.usage.output_tokens",
+      "gen_ai.usage.reasoning.output_tokens",
       "server.address",
       "server.port"
     ],
diff --git a/tests/java/openai/data-prototype.json b/tests/java/openai/data-prototype.json
index fe4767e5..0c2b2515 100644
--- a/tests/java/openai/data-prototype.json
+++ b/tests/java/openai/data-prototype.json
@@ -9,7 +9,8 @@
       "gen_ai.response.model",
       "gen_ai.tool.definitions",
       "gen_ai.usage.input_tokens",
-      "gen_ai.usage.output_tokens"
+      "gen_ai.usage.output_tokens",
+      "gen_ai.usage.reasoning.output_tokens"
     ],
     "embeddings": [
       "gen_ai.operation.name",
diff --git a/tests/java/openai/src/main/java/com/example/openaitest/OpenAiPrototypeTest.java b/tests/java/openai/src/main/java/com/example/openaitest/OpenAiPrototypeTest.java
index 80184029..3c452831 100644
--- a/tests/java/openai/src/main/java/com/example/openaitest/OpenAiPrototypeTest.java
+++ b/tests/java/openai/src/main/java/com/example/openaitest/OpenAiPrototypeTest.java
@@ -89,6 +89,10 @@ static void runChat(OpenAIClient client) {
             completion.usage().ifPresent(usage -> {
                 span.setAttribute(longKey("gen_ai.usage.input_tokens"), usage.promptTokens());
                 span.setAttribute(longKey("gen_ai.usage.output_tokens"), usage.completionTokens());
+                usage.completionTokensDetails().ifPresent(details -> {
+                    details.reasoningTokens().filter(r -> r > 0).ifPresent(reasoning ->
+                        span.setAttribute(longKey("gen_ai.usage.reasoning.output_tokens"), reasoning));
+                });
             });
 
             String content = choice.message().content().orElse("");
@@ -132,6 +136,10 @@ static void runChat(OpenAIClient client) {
                 logBuilder
                     .setAttribute(longKey("gen_ai.usage.input_tokens"), usage.promptTokens())
                     .setAttribute(longKey("gen_ai.usage.output_tokens"), usage.completionTokens());
+                usage.completionTokensDetails().ifPresent(details -> {
+                    details.reasoningTokens().filter(r -> r > 0).ifPresent(reasoning ->
+                        logBuilder.setAttribute(longKey("gen_ai.usage.reasoning.output_tokens"), reasoning));
+                });
             });
             logBuilder.emit();
 
@@ -173,6 +181,10 @@ static void runChatStreaming(OpenAIClient client) {
                     chunk.usage().ifPresent(usage -> {
                         span.setAttribute(longKey("gen_ai.usage.input_tokens"), usage.promptTokens());
                         span.setAttribute(longKey("gen_ai.usage.output_tokens"), usage.completionTokens());
+                        usage.completionTokensDetails().ifPresent(details -> {
+                            details.reasoningTokens().filter(r -> r > 0).ifPresent(reasoning ->
+                                span.setAttribute(longKey("gen_ai.usage.reasoning.output_tokens"), reasoning));
+                        });
                     });
                 });
             } catch (Exception e) {
@@ -238,6 +250,10 @@ static void runChatToolCall(OpenAIClient client) {
             completion.usage().ifPresent(usage -> {
                 span.setAttribute(longKey("gen_ai.usage.input_tokens"), usage.promptTokens());
                 span.setAttribute(longKey("gen_ai.usage.output_tokens"), usage.completionTokens());
+                usage.completionTokensDetails().ifPresent(details -> {
+                    details.reasoningTokens().filter(r -> r > 0).ifPresent(reasoning ->
+                        span.setAttribute(longKey("gen_ai.usage.reasoning.output_tokens"), reasoning));
+                });
             });
 
             List<ChatCompletionMessageToolCall> toolCalls =
diff --git a/tests/js/azure-openai/data-prototype.json b/tests/js/azure-openai/data-prototype.json
index 2ecfb5a3..bbabc72e 100644
--- a/tests/js/azure-openai/data-prototype.json
+++ b/tests/js/azure-openai/data-prototype.json
@@ -10,6 +10,7 @@
       "gen_ai.tool.definitions",
       "gen_ai.usage.input_tokens",
       "gen_ai.usage.output_tokens",
+      "gen_ai.usage.reasoning.output_tokens",
       "server.address",
       "server.port"
     ],
diff --git a/tests/js/azure-openai/test_prototype.ts b/tests/js/azure-openai/test_prototype.ts
index 507d4daf..75fd46f9 100644
--- a/tests/js/azure-openai/test_prototype.ts
+++ b/tests/js/azure-openai/test_prototype.ts
@@ -47,6 +47,9 @@ async function main() {
     if (resp.usage) {
       span.setAttribute("gen_ai.usage.input_tokens", resp.usage.prompt_tokens);
       span.setAttribute("gen_ai.usage.output_tokens", resp.usage.completion_tokens);
+      if (resp.usage.completion_tokens_details?.reasoning_tokens) {
+        span.setAttribute("gen_ai.usage.reasoning.output_tokens", resp.usage.completion_tokens_details.reasoning_tokens);
+      }
     }
 
     // Emit inference operation details event
@@ -62,6 +65,7 @@ async function main() {
         "gen_ai.response.finish_reasons": resp.choices.map(c => c.finish_reason),
         "gen_ai.usage.input_tokens": resp.usage?.prompt_tokens,
         "gen_ai.usage.output_tokens": resp.usage?.completion_tokens,
+        "gen_ai.usage.reasoning.output_tokens": resp.usage?.completion_tokens_details?.reasoning_tokens || undefined,
         "gen_ai.input.messages": JSON.stringify(
           messages.map(m => ({ role: m.role, parts: [{ type: "text", content: m.content }] }))
         ),
@@ -105,6 +109,7 @@ async function main() {
     let finishReason = "";
     let inputTokens = 0;
     let outputTokens = 0;
+    let reasoningTokens: number | undefined;
     for await (const chunk of stream) {
       if (chunk.choices[0]?.delta?.content) {
         text += chunk.choices[0].delta.content;
@@ -117,6 +122,9 @@ async function main() {
       if (chunk.usage) {
         inputTokens = chunk.usage.prompt_tokens;
         outputTokens = chunk.usage.completion_tokens;
+        if (chunk.usage.completion_tokens_details?.reasoning_tokens) {
+          reasoningTokens = chunk.usage.completion_tokens_details.reasoning_tokens;
+        }
       }
     }
     span.setAttribute("gen_ai.response.model", model);
@@ -126,6 +134,7 @@ async function main() {
     }
     if (inputTokens) span.setAttribute("gen_ai.usage.input_tokens", inputTokens);
     if (outputTokens) span.setAttribute("gen_ai.usage.output_tokens", outputTokens);
+    if (reasoningTokens) span.setAttribute("gen_ai.usage.reasoning.output_tokens", reasoningTokens);
     console.log(`    -> ${text.slice(0, 60)}`);
     span.end();
   });
@@ -168,6 +177,9 @@ async function main() {
     if (resp.usage) {
       span.setAttribute("gen_ai.usage.input_tokens", resp.usage.prompt_tokens);
       span.setAttribute("gen_ai.usage.output_tokens", resp.usage.completion_tokens);
+      if (resp.usage.completion_tokens_details?.reasoning_tokens) {
+        span.setAttribute("gen_ai.usage.reasoning.output_tokens", resp.usage.completion_tokens_details.reasoning_tokens);
+      }
     }
     const toolCall = resp.choices[0].message.tool_calls?.[0];
     if (toolCall?.type === "function") {
diff --git a/tests/js/openai/data-prototype.json b/tests/js/openai/data-prototype.json
index 2ecfb5a3..bbabc72e 100644
--- a/tests/js/openai/data-prototype.json
+++ b/tests/js/openai/data-prototype.json
@@ -10,6 +10,7 @@
       "gen_ai.tool.definitions",
       "gen_ai.usage.input_tokens",
       "gen_ai.usage.output_tokens",
+      "gen_ai.usage.reasoning.output_tokens",
       "server.address",
       "server.port"
     ],
diff --git a/tests/js/openai/test_prototype.ts b/tests/js/openai/test_prototype.ts
index ebc21e2f..d9de7d69 100644
--- a/tests/js/openai/test_prototype.ts
+++ b/tests/js/openai/test_prototype.ts
@@ -43,6 +43,9 @@ async function main() {
     if (resp.usage) {
       span.setAttribute("gen_ai.usage.input_tokens", resp.usage.prompt_tokens);
       span.setAttribute("gen_ai.usage.output_tokens", resp.usage.completion_tokens);
+      if (resp.usage.completion_tokens_details?.reasoning_tokens) {
+        span.setAttribute("gen_ai.usage.reasoning.output_tokens", resp.usage.completion_tokens_details.reasoning_tokens);
+      }
     }
 
     // Emit inference operation details event
@@ -58,6 +61,7 @@ async function main() {
         "gen_ai.response.finish_reasons": resp.choices.map(c => c.finish_reason),
         "gen_ai.usage.input_tokens": resp.usage?.prompt_tokens,
         "gen_ai.usage.output_tokens": resp.usage?.completion_tokens,
+        "gen_ai.usage.reasoning.output_tokens": resp.usage?.completion_tokens_details?.reasoning_tokens || undefined,
         "gen_ai.input.messages": JSON.stringify(
           messages.map(m => ({ role: m.role, parts: [{ type: "text", content: m.content }] }))
         ),
@@ -101,6 +105,7 @@ async function main() {
     let finishReason = "";
     let inputTokens = 0;
     let outputTokens = 0;
+    let reasoningTokens: number | undefined;
     for await (const chunk of stream) {
       if (chunk.choices[0]?.delta?.content) {
         text += chunk.choices[0].delta.content;
@@ -113,6 +118,9 @@ async function main() {
       if (chunk.usage) {
         inputTokens = chunk.usage.prompt_tokens;
         outputTokens = chunk.usage.completion_tokens;
+        if (chunk.usage.completion_tokens_details?.reasoning_tokens) {
+          reasoningTokens = chunk.usage.completion_tokens_details.reasoning_tokens;
+        }
       }
     }
     span.setAttribute("gen_ai.response.model", model);
@@ -122,6 +130,7 @@ async function main() {
     }
     if (inputTokens) span.setAttribute("gen_ai.usage.input_tokens", inputTokens);
     if (outputTokens) span.setAttribute("gen_ai.usage.output_tokens", outputTokens);
+    if (reasoningTokens) span.setAttribute("gen_ai.usage.reasoning.output_tokens", reasoningTokens);
     console.log(`    -> ${text.slice(0, 60)}`);
     span.end();
   });
@@ -164,6 +173,9 @@ async function main() {
     if (resp.usage) {
       span.setAttribute("gen_ai.usage.input_tokens", resp.usage.prompt_tokens);
       span.setAttribute("gen_ai.usage.output_tokens", resp.usage.completion_tokens);
+      if (resp.usage.completion_tokens_details?.reasoning_tokens) {
+        span.setAttribute("gen_ai.usage.reasoning.output_tokens", resp.usage.completion_tokens_details.reasoning_tokens);
+      }
     }
     const toolCall = resp.choices[0].message.tool_calls?.[0];
     if (toolCall?.type === "function") {
diff --git a/tests/js/vertexai/data-prototype.json b/tests/js/vertexai/data-prototype.json
index fbc2c8ff..1f6ebe52 100644
--- a/tests/js/vertexai/data-prototype.json
+++ b/tests/js/vertexai/data-prototype.json
@@ -8,7 +8,8 @@
       "gen_ai.response.model",
       "gen_ai.tool.definitions",
       "gen_ai.usage.input_tokens",
-      "gen_ai.usage.output_tokens"
+      "gen_ai.usage.output_tokens",
+      "gen_ai.usage.reasoning.output_tokens"
     ]
   },
   "events": {
diff --git a/tests/js/vertexai/test_prototype.ts b/tests/js/vertexai/test_prototype.ts
index d3eaccc5..8a79f8cd 100644
--- a/tests/js/vertexai/test_prototype.ts
+++ b/tests/js/vertexai/test_prototype.ts
@@ -82,6 +82,9 @@ async function main() {
       if (resp.usageMetadata.candidatesTokenCount) {
         span.setAttribute("gen_ai.usage.output_tokens", resp.usageMetadata.candidatesTokenCount);
       }
+      if ((resp.usageMetadata as any).thoughtsTokenCount) {
+        span.setAttribute("gen_ai.usage.reasoning.output_tokens", (resp.usageMetadata as any).thoughtsTokenCount);
+      }
     }
     const text = candidate?.content?.parts?.[0]?.text ?? "";
 
@@ -97,6 +100,7 @@ async function main() {
         "gen_ai.response.finish_reasons": candidate?.finishReason ? [candidate.finishReason] : undefined,
         "gen_ai.usage.input_tokens": resp.usageMetadata?.promptTokenCount,
         "gen_ai.usage.output_tokens": resp.usageMetadata?.candidatesTokenCount,
+        "gen_ai.usage.reasoning.output_tokens": (resp.usageMetadata as any)?.thoughtsTokenCount || undefined,
         "gen_ai.input.messages": JSON.stringify([
           { role: "user", parts: [{ type: "text", content: userMessage }] }
         ]),
@@ -187,6 +191,9 @@ async function main() {
       if (aggregated.usageMetadata.candidatesTokenCount) {
         span.setAttribute("gen_ai.usage.output_tokens", aggregated.usageMetadata.candidatesTokenCount);
       }
+      if ((aggregated.usageMetadata as any).thoughtsTokenCount) {
+        span.setAttribute("gen_ai.usage.reasoning.output_tokens", (aggregated.usageMetadata as any).thoughtsTokenCount);
+      }
     }
     console.log(`    -> ${text.slice(0, 60)}`);
     span.end();
diff --git a/tests/mock-server/mock_server/server.py b/tests/mock-server/mock_server/server.py
index 57447546..849b9d19 100644
--- a/tests/mock-server/mock_server/server.py
+++ b/tests/mock-server/mock_server/server.py
@@ -36,6 +36,9 @@
         "prompt_tokens": 25,
         "completion_tokens": 12,
         "total_tokens": 37,
+        "completion_tokens_details": {
+            "reasoning_tokens": 5,
+        },
     },
 }
 
@@ -68,6 +71,9 @@
         "prompt_tokens": 50,
         "completion_tokens": 20,
         "total_tokens": 70,
+        "completion_tokens_details": {
+            "reasoning_tokens": 8,
+        },
     },
 }
 
@@ -217,6 +223,9 @@ def _stream_openai_chat(body):
                 "prompt_tokens": 25,
                 "completion_tokens": 6,
                 "total_tokens": 31,
+                "completion_tokens_details": {
+                    "reasoning_tokens": 2,
+                },
             },
         }
     )
@@ -430,6 +439,7 @@ def anthropic_messages():
         "promptTokenCount": 25,
         "candidatesTokenCount": 12,
         "totalTokenCount": 37,
+        "thoughtsTokenCount": 5,
     },
     "modelVersion": "gemini-2.0-flash",
 }
@@ -461,6 +471,7 @@ def _stream_google_genai():
             "promptTokenCount": 25,
             "candidatesTokenCount": 6,
             "totalTokenCount": 31,
+            "thoughtsTokenCount": 2,
         },
     }
     yield json.dumps(final) + "\n"
@@ -515,6 +526,7 @@ def _google_genai_stream_chunks():
             "promptTokenCount": 25,
             "candidatesTokenCount": 6,
             "totalTokenCount": 31,
+            "thoughtsTokenCount": 2,
         },
     })
     return chunks
diff --git a/tests/python/azure-openai/data-prototype.json b/tests/python/azure-openai/data-prototype.json
index 69447190..7ab5f31f 100644
--- a/tests/python/azure-openai/data-prototype.json
+++ b/tests/python/azure-openai/data-prototype.json
@@ -10,6 +10,7 @@
       "gen_ai.tool.definitions",
       "gen_ai.usage.input_tokens",
       "gen_ai.usage.output_tokens",
+      "gen_ai.usage.reasoning.output_tokens",
       "server.address",
       "server.port"
     ],
diff --git a/tests/python/azure-openai/test_prototype.py b/tests/python/azure-openai/test_prototype.py
index 9882a95f..e160f0a7 100644
--- a/tests/python/azure-openai/test_prototype.py
+++ b/tests/python/azure-openai/test_prototype.py
@@ -38,6 +38,9 @@ def run_chat_prototype(client):
         if resp.usage:
             span.set_attribute("gen_ai.usage.input_tokens", resp.usage.prompt_tokens)
             span.set_attribute("gen_ai.usage.output_tokens", resp.usage.completion_tokens)
+            if hasattr(resp.usage, "completion_tokens_details") and resp.usage.completion_tokens_details:
+                if getattr(resp.usage.completion_tokens_details, "reasoning_tokens", None):
+                    span.set_attribute("gen_ai.usage.reasoning.output_tokens", resp.usage.completion_tokens_details.reasoning_tokens)
 
         # Emit inference operation details event
         event_attrs = {
@@ -62,6 +65,9 @@ def run_chat_prototype(client):
         if resp.usage:
             event_attrs["gen_ai.usage.input_tokens"] = resp.usage.prompt_tokens
             event_attrs["gen_ai.usage.output_tokens"] = resp.usage.completion_tokens
+            if hasattr(resp.usage, "completion_tokens_details") and resp.usage.completion_tokens_details:
+                if getattr(resp.usage.completion_tokens_details, "reasoning_tokens", None):
+                    event_attrs["gen_ai.usage.reasoning.output_tokens"] = resp.usage.completion_tokens_details.reasoning_tokens
         if endpoint.hostname:
             event_attrs["server.address"] = endpoint.hostname
         if endpoint.port is not None:
@@ -100,6 +106,7 @@ def run_chat_streaming_prototype(client):
         finish_reasons = []
         input_tokens = None
         output_tokens = None
+        reasoning_tokens = None
         for chunk in stream:
             model = model or getattr(chunk, "model", None)
             response_id = response_id or getattr(chunk, "id", None)
@@ -110,6 +117,9 @@ def run_chat_streaming_prototype(client):
             if chunk.usage:
                 input_tokens = chunk.usage.prompt_tokens
                 output_tokens = chunk.usage.completion_tokens
+                if hasattr(chunk.usage, "completion_tokens_details") and chunk.usage.completion_tokens_details:
+                    if getattr(chunk.usage.completion_tokens_details, "reasoning_tokens", None):
+                        reasoning_tokens = chunk.usage.completion_tokens_details.reasoning_tokens
         if model:
             span.set_attribute("gen_ai.response.model", model)
         if response_id:
@@ -120,6 +130,8 @@ def run_chat_streaming_prototype(client):
             span.set_attribute("gen_ai.usage.input_tokens", input_tokens)
         if output_tokens is not None:
             span.set_attribute("gen_ai.usage.output_tokens", output_tokens)
+        if reasoning_tokens:
+            span.set_attribute("gen_ai.usage.reasoning.output_tokens", reasoning_tokens)
         print(f"    -> {text[:60]}")
 
 
@@ -163,6 +175,9 @@ def run_chat_tool_call_prototype(client):
         if resp.usage:
             span.set_attribute("gen_ai.usage.input_tokens", resp.usage.prompt_tokens)
             span.set_attribute("gen_ai.usage.output_tokens", resp.usage.completion_tokens)
+            if hasattr(resp.usage, "completion_tokens_details") and resp.usage.completion_tokens_details:
+                if getattr(resp.usage.completion_tokens_details, "reasoning_tokens", None):
+                    span.set_attribute("gen_ai.usage.reasoning.output_tokens", resp.usage.completion_tokens_details.reasoning_tokens)
         choice = resp.choices[0]
         if choice.message.tool_calls:
             print(f"    -> tool_call: {choice.message.tool_calls[0].function.name}")
diff --git a/tests/python/google-adk/data-prototype.json b/tests/python/google-adk/data-prototype.json
index 9e6b8431..9b64cf0a 100644
--- a/tests/python/google-adk/data-prototype.json
+++ b/tests/python/google-adk/data-prototype.json
@@ -8,7 +8,8 @@
       "gen_ai.response.finish_reasons",
       "gen_ai.tool.definitions",
       "gen_ai.usage.input_tokens",
-      "gen_ai.usage.output_tokens"
+      "gen_ai.usage.output_tokens",
+      "gen_ai.usage.reasoning.output_tokens"
     ]
   }
 }
diff --git a/tests/python/google-adk/test_prototype.py b/tests/python/google-adk/test_prototype.py
index 3b2e02d4..4f837be3 100644
--- a/tests/python/google-adk/test_prototype.py
+++ b/tests/python/google-adk/test_prototype.py
@@ -147,13 +147,17 @@ async def _run():
                     if usage_metadata is not None:
                         prompt_token_count = getattr(usage_metadata, "prompt_token_count", None)
                         candidate_token_count = getattr(usage_metadata, "candidates_token_count", None)
+                        thoughts_token_count = getattr(usage_metadata, "thoughts_token_count", None)
                         if isinstance(usage_metadata, dict):
                             prompt_token_count = usage_metadata.get("prompt_token_count")
                             candidate_token_count = usage_metadata.get("candidates_token_count")
+                            thoughts_token_count = usage_metadata.get("thoughts_token_count")
                         if prompt_token_count is not None:
                             span.set_attribute("gen_ai.usage.input_tokens", prompt_token_count)
                         if candidate_token_count is not None:
                             span.set_attribute("gen_ai.usage.output_tokens", candidate_token_count)
+                        if thoughts_token_count:
+                            span.set_attribute("gen_ai.usage.reasoning.output_tokens", thoughts_token_count)
                     if finish_reason is not None:
                         span.set_attribute(
                             "gen_ai.response.finish_reasons",
diff --git a/tests/python/google-genai/data-prototype.json b/tests/python/google-genai/data-prototype.json
index 9a34ebb5..7c20574b 100644
--- a/tests/python/google-genai/data-prototype.json
+++ b/tests/python/google-genai/data-prototype.json
@@ -8,7 +8,8 @@
       "gen_ai.response.model",
       "gen_ai.tool.definitions",
       "gen_ai.usage.input_tokens",
-      "gen_ai.usage.output_tokens"
+      "gen_ai.usage.output_tokens",
+      "gen_ai.usage.reasoning.output_tokens"
     ],
     "embeddings": [
       "gen_ai.operation.name",
diff --git a/tests/python/google-genai/test_prototype.py b/tests/python/google-genai/test_prototype.py
index 1b1deda3..75dfb168 100644
--- a/tests/python/google-genai/test_prototype.py
+++ b/tests/python/google-genai/test_prototype.py
@@ -48,6 +48,8 @@ def run_chat():
                 span.set_attribute("gen_ai.usage.input_tokens", response.usage_metadata.prompt_token_count)
             if hasattr(response.usage_metadata, "candidates_token_count") and response.usage_metadata.candidates_token_count:
                 span.set_attribute("gen_ai.usage.output_tokens", response.usage_metadata.candidates_token_count)
+            if hasattr(response.usage_metadata, "thoughts_token_count") and response.usage_metadata.thoughts_token_count:
+                span.set_attribute("gen_ai.usage.reasoning.output_tokens", response.usage_metadata.thoughts_token_count)
 
         # Emit inference operation details event
         event_attrs = {
@@ -73,6 +75,8 @@ def run_chat():
                 event_attrs["gen_ai.usage.input_tokens"] = response.usage_metadata.prompt_token_count
             if hasattr(response.usage_metadata, "candidates_token_count") and response.usage_metadata.candidates_token_count:
                 event_attrs["gen_ai.usage.output_tokens"] = response.usage_metadata.candidates_token_count
+            if hasattr(response.usage_metadata, "thoughts_token_count") and response.usage_metadata.thoughts_token_count:
+                event_attrs["gen_ai.usage.reasoning.output_tokens"] = response.usage_metadata.thoughts_token_count
         get_logger_provider().get_logger("gen_ai.prototype").emit(
             event_name="gen_ai.client.inference.operation.details",
             body="Inference operation details",
@@ -187,6 +191,8 @@ def run_chat_streaming():
                 span.set_attribute("gen_ai.usage.input_tokens", last_chunk.usage_metadata.prompt_token_count)
             if hasattr(last_chunk.usage_metadata, "candidates_token_count") and last_chunk.usage_metadata.candidates_token_count:
                 span.set_attribute("gen_ai.usage.output_tokens", last_chunk.usage_metadata.candidates_token_count)
+            if hasattr(last_chunk.usage_metadata, "thoughts_token_count") and last_chunk.usage_metadata.thoughts_token_count:
+                span.set_attribute("gen_ai.usage.reasoning.output_tokens", last_chunk.usage_metadata.thoughts_token_count)
         print(f"    -> {text[:60]}")
 
 
diff --git a/tests/python/openai/data-prototype.json b/tests/python/openai/data-prototype.json
index 69447190..7ab5f31f 100644
--- a/tests/python/openai/data-prototype.json
+++ b/tests/python/openai/data-prototype.json
@@ -10,6 +10,7 @@
       "gen_ai.tool.definitions",
       "gen_ai.usage.input_tokens",
       "gen_ai.usage.output_tokens",
+      "gen_ai.usage.reasoning.output_tokens",
       "server.address",
       "server.port"
     ],
diff --git a/tests/python/openai/test_prototype.py b/tests/python/openai/test_prototype.py
index e7be94b5..4b3be295 100644
--- a/tests/python/openai/test_prototype.py
+++ b/tests/python/openai/test_prototype.py
@@ -38,6 +38,9 @@ def run_chat_prototype(client):
         if resp.usage:
             span.set_attribute("gen_ai.usage.input_tokens", resp.usage.prompt_tokens)
             span.set_attribute("gen_ai.usage.output_tokens", resp.usage.completion_tokens)
+            if hasattr(resp.usage, "completion_tokens_details") and resp.usage.completion_tokens_details:
+                if getattr(resp.usage.completion_tokens_details, "reasoning_tokens", None):
+                    span.set_attribute("gen_ai.usage.reasoning.output_tokens", resp.usage.completion_tokens_details.reasoning_tokens)
 
         # Emit inference operation details event
         event_attrs = {
@@ -62,6 +65,9 @@ def run_chat_prototype(client):
         if resp.usage:
             event_attrs["gen_ai.usage.input_tokens"] = resp.usage.prompt_tokens
             event_attrs["gen_ai.usage.output_tokens"] = resp.usage.completion_tokens
+            if hasattr(resp.usage, "completion_tokens_details") and resp.usage.completion_tokens_details:
+                if getattr(resp.usage.completion_tokens_details, "reasoning_tokens", None):
+                    event_attrs["gen_ai.usage.reasoning.output_tokens"] = resp.usage.completion_tokens_details.reasoning_tokens
         if endpoint.hostname:
             event_attrs["server.address"] = endpoint.hostname
         if endpoint.port is not None:
@@ -100,6 +106,7 @@ def run_chat_streaming_prototype(client):
         finish_reasons = []
         input_tokens = None
         output_tokens = None
+        reasoning_tokens = None
         for chunk in stream:
             model = model or getattr(chunk, "model", None)
             response_id = response_id or getattr(chunk, "id", None)
@@ -110,6 +117,9 @@ def run_chat_streaming_prototype(client):
             if chunk.usage:
                 input_tokens = chunk.usage.prompt_tokens
                 output_tokens = chunk.usage.completion_tokens
+                if hasattr(chunk.usage, "completion_tokens_details") and chunk.usage.completion_tokens_details:
+                    if getattr(chunk.usage.completion_tokens_details, "reasoning_tokens", None):
+                        reasoning_tokens = chunk.usage.completion_tokens_details.reasoning_tokens
         if model:
             span.set_attribute("gen_ai.response.model", model)
         if response_id:
@@ -120,6 +130,8 @@ def run_chat_streaming_prototype(client):
             span.set_attribute("gen_ai.usage.input_tokens", input_tokens)
         if output_tokens is not None:
             span.set_attribute("gen_ai.usage.output_tokens", output_tokens)
+        if reasoning_tokens:
+            span.set_attribute("gen_ai.usage.reasoning.output_tokens", reasoning_tokens)
         print(f"    -> {text[:60]}")
 
 
@@ -163,6 +175,9 @@ def run_chat_tool_call_prototype(client):
         if resp.usage:
             span.set_attribute("gen_ai.usage.input_tokens", resp.usage.prompt_tokens)
             span.set_attribute("gen_ai.usage.output_tokens", resp.usage.completion_tokens)
+            if hasattr(resp.usage, "completion_tokens_details") and resp.usage.completion_tokens_details:
+                if getattr(resp.usage.completion_tokens_details, "reasoning_tokens", None):
+                    span.set_attribute("gen_ai.usage.reasoning.output_tokens", resp.usage.completion_tokens_details.reasoning_tokens)
         choice = resp.choices[0]
         if choice.message.tool_calls:
             print(f"    -> tool_call: {choice.message.tool_calls[0].function.name}")
diff --git a/tests/python/vertexai/data-prototype.json b/tests/python/vertexai/data-prototype.json
index fbc2c8ff..1f6ebe52 100644
--- a/tests/python/vertexai/data-prototype.json
+++ b/tests/python/vertexai/data-prototype.json
@@ -8,7 +8,8 @@
       "gen_ai.response.model",
       "gen_ai.tool.definitions",
       "gen_ai.usage.input_tokens",
-      "gen_ai.usage.output_tokens"
+      "gen_ai.usage.output_tokens",
+      "gen_ai.usage.reasoning.output_tokens"
     ]
   },
   "events": {
diff --git a/tests/python/vertexai/test_prototype.py b/tests/python/vertexai/test_prototype.py
index 47cbd8e6..25faa64b 100644
--- a/tests/python/vertexai/test_prototype.py
+++ b/tests/python/vertexai/test_prototype.py
@@ -80,6 +80,8 @@ def run_chat():
                 span.set_attribute("gen_ai.usage.input_tokens", response.usage_metadata.prompt_token_count)
             if response.usage_metadata.candidates_token_count:
                 span.set_attribute("gen_ai.usage.output_tokens", response.usage_metadata.candidates_token_count)
+            if hasattr(response.usage_metadata, "thoughts_token_count") and response.usage_metadata.thoughts_token_count:
+                span.set_attribute("gen_ai.usage.reasoning.output_tokens", response.usage_metadata.thoughts_token_count)
 
         # Emit inference operation details event
         event_attrs = {
@@ -104,6 +106,8 @@ def run_chat():
                 event_attrs["gen_ai.usage.input_tokens"] = response.usage_metadata.prompt_token_count
             if response.usage_metadata.candidates_token_count:
                 event_attrs["gen_ai.usage.output_tokens"] = response.usage_metadata.candidates_token_count
+            if hasattr(response.usage_metadata, "thoughts_token_count") and response.usage_metadata.thoughts_token_count:
+                event_attrs["gen_ai.usage.reasoning.output_tokens"] = response.usage_metadata.thoughts_token_count
         get_logger_provider().get_logger("gen_ai.prototype").emit(
             event_name="gen_ai.client.inference.operation.details",
             body="Inference operation details",
@@ -207,6 +211,8 @@ def run_chat_streaming():
                 span.set_attribute("gen_ai.usage.input_tokens", last_chunk.usage_metadata.prompt_token_count)
             if last_chunk.usage_metadata.candidates_token_count:
                 span.set_attribute("gen_ai.usage.output_tokens", last_chunk.usage_metadata.candidates_token_count)
+            if hasattr(last_chunk.usage_metadata, "thoughts_token_count") and last_chunk.usage_metadata.thoughts_token_count:
+                span.set_attribute("gen_ai.usage.reasoning.output_tokens", last_chunk.usage_metadata.thoughts_token_count)
         print(f"    -> {text[:60]}")