docs(vertex.md): add thinking/reasoning content for gemini models to docs

docs/my-website/docs/providers/vertex.md

@@ -542,6 +542,154 @@ print(resp)
 ```
 
 
+### **Thinking / `reasoning_content`**
+
+LiteLLM translates OpenAI's `reasoning_effort` to Gemini's `thinking` parameter. [Code](https://github.com/BerriAI/litellm/blob/620664921902d7a9bfb29897a7b27c1a7ef4ddfb/litellm/llms/vertex_ai/gemini/vertex_and_google_ai_studio_gemini.py#L362)
+
+**Mapping**
+
+| reasoning_effort | thinking |
+| ---------------- | -------- |
+| "low"            | "budget_tokens": 1024 |
+| "medium"         | "budget_tokens": 2048 |
+| "high"           | "budget_tokens": 4096 |
+
+<Tabs>
+<TabItem value="sdk" label="SDK">
+
+```python
+from litellm import completion
+
+# !gcloud auth application-default login - run this to add vertex credentials to your env
+
+resp = completion(
+    model="vertex_ai/gemini-2.5-flash-preview-04-17",
+    messages=[{"role": "user", "content": "What is the capital of France?"}],
+    reasoning_effort="low",
+    vertex_project="project-id",
+    vertex_location="us-central1"
+)
+
+```
+
+</TabItem>
+
+<TabItem value="proxy" label="PROXY">
+
+1. Setup config.yaml
+
+```yaml
+- model_name: gemini-2.5-flash
+  litellm_params:
+    model: vertex_ai/gemini-2.5-flash-preview-04-17
+    vertex_credentials: {"project_id": "project-id", "location": "us-central1", "project_key": "project-key"}
+    vertex_project: "project-id"
+    vertex_location: "us-central1"
+```
+
+2. Start proxy
+
+```bash
+litellm --config /path/to/config.yaml
+```
+
+3. Test it! 
+
+```bash
+curl http://0.0.0.0:4000/v1/chat/completions \
+  -H "Content-Type: application/json" \
+  -H "Authorization: Bearer <YOUR-LITELLM-KEY>" \
+  -d '{
+    "model": "gemini-2.5-flash",
+    "messages": [{"role": "user", "content": "What is the capital of France?"}],
+    "reasoning_effort": "low"
+  }'
+```
+
+</TabItem>
+</Tabs>
+
+
+**Expected Response**
+
+```python
+ModelResponse(
+    id='chatcmpl-c542d76d-f675-4e87-8e5f-05855f5d0f5e',
+    created=1740470510,
+    model='claude-3-7-sonnet-20250219',
+    object='chat.completion',
+    system_fingerprint=None,
+    choices=[
+        Choices(
+            finish_reason='stop',
+            index=0,
+            message=Message(
+                content="The capital of France is Paris.",
+                role='assistant',
+                tool_calls=None,
+                function_call=None,
+                reasoning_content='The capital of France is Paris. This is a very straightforward factual question.'
+            ),
+        )
+    ],
+    usage=Usage(
+        completion_tokens=68,
+        prompt_tokens=42,
+        total_tokens=110,
+        completion_tokens_details=None,
+        prompt_tokens_details=PromptTokensDetailsWrapper(
+            audio_tokens=None,
+            cached_tokens=0,
+            text_tokens=None,
+            image_tokens=None
+        ),
+        cache_creation_input_tokens=0,
+        cache_read_input_tokens=0
+    )
+)
+```
+
+#### Pass `thinking` to Gemini models
+
+You can also pass the `thinking` parameter to Gemini models.
+
+This is translated to Gemini's [`thinkingConfig` parameter](https://ai.google.dev/gemini-api/docs/thinking#set-budget).
+
+<Tabs>
+<TabItem value="sdk" label="SDK">
+
+```python
+from litellm import completion
+
+# !gcloud auth application-default login - run this to add vertex credentials to your env
+
+response = litellm.completion(
+  model="vertex_ai/gemini-2.5-flash-preview-04-17",
+  messages=[{"role": "user", "content": "What is the capital of France?"}],
+  thinking={"type": "enabled", "budget_tokens": 1024},
+  vertex_project="project-id",
+  vertex_location="us-central1"
+)
+```
+
+</TabItem>
+<TabItem value="proxy" label="PROXY">
+
+```bash
+curl http://0.0.0.0:4000/v1/chat/completions \
+  -H "Content-Type: application/json" \
+  -H "Authorization: Bearer $LITELLM_KEY" \
+  -d '{
+    "model": "vertex_ai/gemini-2.5-flash-preview-04-17",
+    "messages": [{"role": "user", "content": "What is the capital of France?"}],
+    "thinking": {"type": "enabled", "budget_tokens": 1024}
+  }'
+```
+
+</TabItem>
+</Tabs>
+
+
 ### **Context Caching**
 
 Use Vertex AI context caching is supported by calling provider api directly. (Unified Endpoint support comin soon.).

docs/my-website/release_notes/v1.67.0-stable/index.md

@@ -41,7 +41,7 @@ hide_table_of_contents: false
     1. New mapped bedrock regions - [PR](https://github.com/BerriAI/litellm/pull/9430)
 - **VertexAI / Google AI Studio**
     1. Gemini - Response format - Retain schema field ordering for google gemini and vertex by specifying propertyOrdering - [Get Started](../../docs/providers/vertex#json-schema), [PR](https://github.com/BerriAI/litellm/pull/9828)
-    2. Gemini-2.5-flash - return reasoning content [ADD DOCS HERE], [PR](https://github.com/BerriAI/litellm/pull/10125)
+    2. Gemini-2.5-flash - return reasoning content [Google AI Studio](../../docs/providers/gemini#usage---thinking--reasoning_content), [Vertex AI](../../docs/providers/vertex#thinking--reasoning_content)
     3. Gemini-2.5-flash - pricing + model information [PR](https://github.com/BerriAI/litellm/pull/10125)
     4. Passthrough - new `/vertex_ai/discovery` route - enables calling AgentBuilder API routes [ADD DOCS HERE], [PR](https://github.com/BerriAI/litellm/pull/10084)
 - **Fireworks AI**