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 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. </Tip>

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.

rust

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</Note> The longer form uses a named client, and supports adding any parameters supported by the provider or changing the temperature, top_p, etc.

rust

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 for a list of supported providers and models, the default options, and setting retry policies.

<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. </Tip>

Using client "<provider>/<model>"

Using a named client

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