# tensorplay.nn.attention.activate_flash_attention_impl

Source: https://www.tensorplay.cn/docs/generated/tensorplay.nn.attention.activate_flash_attention_impl.html

```python
tensorplay.nn.attention.activate_flash_attention_impl(impl: str | Literal['FA3', 'FA4']) → None
```

Activate into the dispatcher a previously registered flash attention impl.

> **Note**
>
> Backend providers should NOT automatically activate their implementation on import. Users should explicitly opt-in by calling this function or via environment variables to ensure multiple provider libraries can coexist.

Parameters:

impl – Implementation identifier to activate. See
[list_flash_attention_impls()](/docs/generated/tensorplay.nn.attention.list_flash_attention_impls.html#tensorplay.nn.attention.list_flash_attention_impls) for available
implementations.
If the backend’s [register_flash_attention_impl()](/docs/generated/tensorplay.nn.attention.register_flash_attention_impl.html#tensorplay.nn.attention.register_flash_attention_impl) callable
returns a FlashAttentionHandle, the registry keeps that
handle alive for the lifetime of the process (until explicit
uninstall support exists).

Example

```
>>> activate_flash_attention_impl("FA4")
```