diff --git a/instrumentation-genai/opentelemetry-instrumentation-openai-v2/CHANGELOG.md b/instrumentation-genai/opentelemetry-instrumentation-openai-v2/CHANGELOG.md
index 9da6770271..0a7aebb9b2 100644
--- a/instrumentation-genai/opentelemetry-instrumentation-openai-v2/CHANGELOG.md
+++ b/instrumentation-genai/opentelemetry-instrumentation-openai-v2/CHANGELOG.md
@@ -7,6 +7,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## Unreleased
 
+- Fix service tier attribute names: use `GEN_AI_OPENAI_REQUEST_SERVICE_TIER` for request
+  attributes and `GEN_AI_OPENAI_RESPONSE_SERVICE_TIER` for response attributes.
+  ([#3920](https://github.com/open-telemetry/opentelemetry-python-contrib/issues/3920))
 - Added support for OpenAI embeddings instrumentation
   ([#3461](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/3461))
 - Record prompt and completion events regardless of span sampling decision.
diff --git a/instrumentation-genai/opentelemetry-instrumentation-openai-v2/src/opentelemetry/instrumentation/openai_v2/patch.py b/instrumentation-genai/opentelemetry-instrumentation-openai-v2/src/opentelemetry/instrumentation/openai_v2/patch.py
index 4d4b4871a4..b51a8aa83c 100644
--- a/instrumentation-genai/opentelemetry-instrumentation-openai-v2/src/opentelemetry/instrumentation/openai_v2/patch.py
+++ b/instrumentation-genai/opentelemetry-instrumentation-openai-v2/src/opentelemetry/instrumentation/openai_v2/patch.py
@@ -370,7 +370,7 @@ def _set_response_attributes(
     if getattr(result, "service_tier", None):
         set_span_attribute(
             span,
-            GenAIAttributes.GEN_AI_OPENAI_REQUEST_SERVICE_TIER,
+            GenAIAttributes.GEN_AI_OPENAI_RESPONSE_SERVICE_TIER,
             result.service_tier,
         )
 
diff --git a/instrumentation-genai/opentelemetry-instrumentation-openai-v2/src/opentelemetry/instrumentation/openai_v2/utils.py b/instrumentation-genai/opentelemetry-instrumentation-openai-v2/src/opentelemetry/instrumentation/openai_v2/utils.py
index 739e6e9207..a96649b796 100644
--- a/instrumentation-genai/opentelemetry-instrumentation-openai-v2/src/opentelemetry/instrumentation/openai_v2/utils.py
+++ b/instrumentation-genai/opentelemetry-instrumentation-openai-v2/src/opentelemetry/instrumentation/openai_v2/utils.py
@@ -230,8 +230,13 @@ def get_llm_request_attributes(
                     GenAIAttributes.GEN_AI_OPENAI_REQUEST_RESPONSE_FORMAT
                 ] = response_format
 
+        # service_tier can be passed directly or in extra_body (in SDK 1.26.0 it's via extra_body)
         service_tier = kwargs.get("service_tier")
-        attributes[GenAIAttributes.GEN_AI_OPENAI_RESPONSE_SERVICE_TIER] = (
+        if service_tier is None:
+            extra_body = kwargs.get("extra_body")
+            if isinstance(extra_body, Mapping):
+                service_tier = extra_body.get("service_tier")
+        attributes[GenAIAttributes.GEN_AI_OPENAI_REQUEST_SERVICE_TIER] = (
             service_tier if service_tier != "auto" else None
         )
 
diff --git a/instrumentation-genai/opentelemetry-instrumentation-openai-v2/tests/test_async_chat_completions.py b/instrumentation-genai/opentelemetry-instrumentation-openai-v2/tests/test_async_chat_completions.py
index f618267e6b..59594c028b 100644
--- a/instrumentation-genai/opentelemetry-instrumentation-openai-v2/tests/test_async_chat_completions.py
+++ b/instrumentation-genai/opentelemetry-instrumentation-openai-v2/tests/test_async_chat_completions.py
@@ -183,6 +183,8 @@ async def test_async_chat_completion_extra_params(
         response.model,
         response.usage.prompt_tokens,
         response.usage.completion_tokens,
+        request_service_tier="default",
+        response_service_tier=getattr(response, "service_tier", None),
     )
     assert (
         spans[0].attributes[GenAIAttributes.GEN_AI_OPENAI_REQUEST_SEED] == 42
diff --git a/instrumentation-genai/opentelemetry-instrumentation-openai-v2/tests/test_chat_completions.py b/instrumentation-genai/opentelemetry-instrumentation-openai-v2/tests/test_chat_completions.py
index 471d70fcdb..00a3c7c88c 100644
--- a/instrumentation-genai/opentelemetry-instrumentation-openai-v2/tests/test_chat_completions.py
+++ b/instrumentation-genai/opentelemetry-instrumentation-openai-v2/tests/test_chat_completions.py
@@ -221,6 +221,8 @@ def test_chat_completion_extra_params(
         response.model,
         response.usage.prompt_tokens,
         response.usage.completion_tokens,
+        request_service_tier="default",
+        response_service_tier=getattr(response, "service_tier", None),
     )
     assert (
         spans[0].attributes[GenAIAttributes.GEN_AI_OPENAI_REQUEST_SEED] == 42
diff --git a/instrumentation-genai/opentelemetry-instrumentation-openai-v2/tests/test_utils.py b/instrumentation-genai/opentelemetry-instrumentation-openai-v2/tests/test_utils.py
index eb66eb7c7a..d4d64c4027 100644
--- a/instrumentation-genai/opentelemetry-instrumentation-openai-v2/tests/test_utils.py
+++ b/instrumentation-genai/opentelemetry-instrumentation-openai-v2/tests/test_utils.py
@@ -25,6 +25,14 @@
 )
 
 
+def _assert_optional_attribute(span, attribute_name, expected_value):
+    """Helper to assert optional span attributes."""
+    if expected_value is not None:
+        assert expected_value == span.attributes[attribute_name]
+    else:
+        assert attribute_name not in span.attributes
+
+
 def assert_all_attributes(
     span: ReadableSpan,
     request_model: str,
@@ -35,6 +43,8 @@ def assert_all_attributes(
     operation_name: str = "chat",
     server_address: str = "api.openai.com",
     server_port: int = 443,
+    request_service_tier: Optional[str] = None,
+    response_service_tier: Optional[str] = None,
 ):
     assert span.name == f"{operation_name} {request_model}"
     assert (
@@ -49,44 +59,35 @@ def assert_all_attributes(
         request_model == span.attributes[GenAIAttributes.GEN_AI_REQUEST_MODEL]
     )
 
-    if response_model:
-        assert (
-            response_model
-            == span.attributes[GenAIAttributes.GEN_AI_RESPONSE_MODEL]
-        )
-    else:
-        assert GenAIAttributes.GEN_AI_RESPONSE_MODEL not in span.attributes
-
-    if response_id:
-        assert (
-            response_id == span.attributes[GenAIAttributes.GEN_AI_RESPONSE_ID]
-        )
-    else:
-        assert GenAIAttributes.GEN_AI_RESPONSE_ID not in span.attributes
-
-    if input_tokens:
-        assert (
-            input_tokens
-            == span.attributes[GenAIAttributes.GEN_AI_USAGE_INPUT_TOKENS]
-        )
-    else:
-        assert GenAIAttributes.GEN_AI_USAGE_INPUT_TOKENS not in span.attributes
-
-    if output_tokens:
-        assert (
-            output_tokens
-            == span.attributes[GenAIAttributes.GEN_AI_USAGE_OUTPUT_TOKENS]
-        )
-    else:
-        assert (
-            GenAIAttributes.GEN_AI_USAGE_OUTPUT_TOKENS not in span.attributes
-        )
+    _assert_optional_attribute(
+        span, GenAIAttributes.GEN_AI_RESPONSE_MODEL, response_model
+    )
+    _assert_optional_attribute(
+        span, GenAIAttributes.GEN_AI_RESPONSE_ID, response_id
+    )
+    _assert_optional_attribute(
+        span, GenAIAttributes.GEN_AI_USAGE_INPUT_TOKENS, input_tokens
+    )
+    _assert_optional_attribute(
+        span, GenAIAttributes.GEN_AI_USAGE_OUTPUT_TOKENS, output_tokens
+    )
 
     assert server_address == span.attributes[ServerAttributes.SERVER_ADDRESS]
 
     if server_port != 443 and server_port > 0:
         assert server_port == span.attributes[ServerAttributes.SERVER_PORT]
 
+    _assert_optional_attribute(
+        span,
+        GenAIAttributes.GEN_AI_OPENAI_REQUEST_SERVICE_TIER,
+        request_service_tier,
+    )
+    _assert_optional_attribute(
+        span,
+        GenAIAttributes.GEN_AI_OPENAI_RESPONSE_SERVICE_TIER,
+        response_service_tier,
+    )
+
 
 def assert_log_parent(log, span):
     """Assert that the log record has the correct parent span context"""