client Option

The client option provides a simple way to override which LLM client a function uses at runtime. It’s a shorthand for creating a ClientRegistry and calling set_primary().

Quick Start

from baml_client import b
# Use shorthand provider/model syntax
result = await b.ExtractResume("...", baml_options={"client": "openai/gpt-4o-mini"})
# Use OpenRouter for open-source models
result = await b.ExtractResume("...", baml_options={"client": "openrouter/meta-llama/llama-3.1-70b-instruct"})
# Or reference a client defined in your .baml files
result = await b.ExtractResume("...", baml_options={"client": "MyCustomClient"})
# Use with_options to set for multiple calls
my_b = b.with_options(client="openai/gpt-4o-mini")
result1 = await my_b.ExtractResume("...")
result2 = await my_b.ExtractInvoice("...")

When to Use

Use the client option when you want to:

• Quickly switch between different LLM providers or models
• A/B test different models
• Use different clients for different environments (dev vs prod)
• Override the default client defined in your .baml files

Precedence

If you provide both client and client_registry, the client option takes precedence:

from baml_py import ClientRegistry
cr = ClientRegistry()
cr.set_primary("ModelA")
# "ModelB" will be used, not "ModelA"
result = await b.ExtractResume("...", baml_options={
    "client": "ModelB",
    "client_registry": cr
})

Valid Client Names

The client value can be:

1. Shorthand provider/model syntax - Use provider/model format for quick access:

   • "openai/gpt-4o-mini" - OpenAI models
   • "anthropic/claude-sonnet-4-20250514" - Anthropic models
   • "openrouter/meta-llama/llama-3.1-70b-instruct" - OpenRouter models
   • "google-ai/gemini-3.5-flash" - Google AI models

2. Client defined in .baml files - Reference by name (e.g., "MyCustomClient")

If the client name is not found, you’ll get a runtime error when the function is called.

Comparison with ClientRegistry

Use client for simple overrides. Use ClientRegistry when you need to add new clients or customize client options at runtime.

Related Topics

• ClientRegistry - For advanced client configuration
• with_options - Set default options for a client