From 4b33bfed412446ca2eea3502ffb2f8d9f67e8464 Mon Sep 17 00:00:00 2001
From: Ritika shrestha <87307821+ritsth@users.noreply.github.com>
Date: Mon, 29 Jun 2026 13:07:48 -0700
Subject: [PATCH] fix(vertex_ai): do not advertise logprobs for gemini 3+
 models

Gemini 3+ does not support logprobs on Vertex AI, but get_supported_openai_params
listed logprobs/top_logprobs unconditionally, so the params were forwarded and
Vertex returned an opaque 400. Gate them behind _is_gemini_3_or_newer, matching
the existing penalty-parameter handling, so logprobs is dropped (or cleanly
rejected) for gemini 3+ while gemini 2.x keeps it.

Fixes #31600
---
 .../vertex_and_google_ai_studio_gemini.py       |  6 ++++--
 .../test_vertex_and_google_ai_studio_gemini.py  | 17 +++++++++++++++++
 2 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/litellm/llms/vertex_ai/gemini/vertex_and_google_ai_studio_gemini.py b/litellm/llms/vertex_ai/gemini/vertex_and_google_ai_studio_gemini.py
index 678877c0721..58096f6bd83 100644
--- a/litellm/llms/vertex_ai/gemini/vertex_and_google_ai_studio_gemini.py
+++ b/litellm/llms/vertex_ai/gemini/vertex_and_google_ai_studio_gemini.py
@@ -325,8 +325,6 @@ class VertexGeminiConfig(VertexAIBaseConfig, BaseConfig):
             "stop",
             "extra_headers",
             "seed",
-            "logprobs",
-            "top_logprobs",
             "modalities",
             "audio",
             "parallel_tool_calls",
@@ -339,6 +337,10 @@ class VertexGeminiConfig(VertexAIBaseConfig, BaseConfig):
         if self._supports_penalty_parameters(model):
             supported_params.extend(["frequency_penalty", "presence_penalty"])
 
+        # Gemini 3+ models do not support logprobs on Vertex AI
+        if not VertexGeminiConfig._is_gemini_3_or_newer(model):
+            supported_params.extend(["logprobs", "top_logprobs"])
+
         if supports_reasoning(model):
             supported_params.append("reasoning_effort")
             supported_params.append("thinking")
diff --git a/tests/test_litellm/llms/vertex_ai/gemini/test_vertex_and_google_ai_studio_gemini.py b/tests/test_litellm/llms/vertex_ai/gemini/test_vertex_and_google_ai_studio_gemini.py
index 20e7aec377b..b6bc50dd305 100644
--- a/tests/test_litellm/llms/vertex_ai/gemini/test_vertex_and_google_ai_studio_gemini.py
+++ b/tests/test_litellm/llms/vertex_ai/gemini/test_vertex_and_google_ai_studio_gemini.py
@@ -5210,3 +5210,20 @@ class TestModelResponseIteratorCleanup:
 
         mock_iterator.aclose.assert_awaited_once()
         mock_response.aclose.assert_awaited_once()
+
+
+@pytest.mark.parametrize(
+    "model, expect_logprobs",
+    [
+        ("gemini-2.5-flash", True),
+        ("gemini-2.5-pro", True),
+        ("gemini-3.5-flash", False),
+        ("gemini-3-pro-preview", False),
+        ("gemini-3.1-flash", False),
+    ],
+)
+def test_logprobs_not_advertised_for_gemini_3(model, expect_logprobs):
+    """Gemini 3+ does not support logprobs on Vertex AI (#31600)."""
+    params = VertexGeminiConfig().get_supported_openai_params(model)
+    assert ("logprobs" in params) is expect_logprobs
+    assert ("top_logprobs" in params) is expect_logprobs