# VertexAICallbackHandler

> **Class** in `langchain_google_vertexai`

📖 [View in docs](https://reference.langchain.com/python/langchain-google-vertexai/callbacks/VertexAICallbackHandler)

Callback Handler that tracks VertexAI info.

## Signature

```python
VertexAICallbackHandler(
    self,
)
```

## Extends

- `BaseCallbackHandler`

## Constructors

```python
__init__(
    self,
) -> None
```


## Properties

- `prompt_tokens`
- `prompt_characters`
- `completion_tokens`
- `completion_characters`
- `successful_requests`
- `total_tokens`
- `cached_tokens`
- `always_verbose`

## Methods

- [`on_llm_start()`](https://reference.langchain.com/python/langchain-google-vertexai/callbacks/VertexAICallbackHandler/on_llm_start)
- [`on_llm_new_token()`](https://reference.langchain.com/python/langchain-google-vertexai/callbacks/VertexAICallbackHandler/on_llm_new_token)
- [`on_llm_end()`](https://reference.langchain.com/python/langchain-google-vertexai/callbacks/VertexAICallbackHandler/on_llm_end)

---

[View source on GitHub](https://github.com/langchain-ai/langchain-google/blob/982e4015b249de8b9ba1e787746d8cc1f6d6b790/libs/vertexai/langchain_google_vertexai/callbacks.py#L10)