> Version notice: This site documents BAML v0, the legacy DSL. BAML v1 is a separate, fully featured programming language in public beta. If the user intends to use BAML v1, ignore this site's content and use the BAML v1 documentation instead. If the intended version is unclear, clarify it before using this page.
> For clean Markdown of any page, append .md to the page URL. For the complete documentation index, see https://docs.boundaryml.com/llms.txt. For MCP access, connect to https://docs.boundaryml.com/_mcp/server.

# Switching LLMs

BAML Supports getting structured output from **all** major providers as well as all OpenAI-API compatible open-source models. See [LLM Providers Reference](/ref/llm-client-providers/open-ai) for how to set each one up.

> **Tip**
>
> BAML can help you get structured output from **any Open-Source model**, with better performance than other techniques, even when it's not officially supported via a Tool-Use API (like o1-preview) or fine-tuned for it! [Read more about how BAML does this](https://www.boundaryml.com/blog/schema-aligned-parsing).

### Using `client "<provider>/<model>"`

Using `openai/model-name` or `anthropic/model-name` will assume you have the ANTHROPIC\_API\_KEY or OPENAI\_API\_KEY environment variables set.

**`BAML`**

```rust BAML
function MakeHaiku(topic: string) -> string {
  client "openai-responses/gpt-5-mini" // or anthropic/claude-sonnet-4-20250514
  prompt #"
    Write a haiku about {{ topic }}.
  "#
}
```

### Using a named client

> **Note**
>
> Use this if you are using open-source models or need customization

The longer form uses a named client, and supports adding any parameters supported by the provider or changing the temperature, top\_p, etc.

**`BAML`**

```rust BAML
client<llm> MyClient {
  provider "openai"
  options {
    model "gpt-5-mini"
    api_key env.OPENAI_API_KEY
    // other params like temperature, top_p, etc.
    temperature 0.0
    base_url "https://my-custom-endpoint.com/v1"
    // add headers
    headers {
      "anthropic-beta" "prompt-caching-2024-07-31"
    }
  }

}

function MakeHaiku(topic: string) -> string {
  client MyClient
  prompt #"
    Write a haiku about {{ topic }}.
  "#
}
```

Consult the [provider documentation](/ref/llm-client-providers/open-ai) for a list of supported providers
and models, the default options, and setting [retry policies](/ref/llm-client-strategies/retry-policy).

> **Tip**
>
> If you want to specify which client to use at runtime, in your Python/TS/Ruby code,
> you can use the [client registry](/ref/baml_client/client-registry) to do so.
>
> This can come in handy if you're trying to, say, send 10% of your requests to a
> different model.