Skip to main content

/v1/messages

Use LiteLLM to call all your LLM APIs in the Anthropic v1/messages format.

Overview​

FeatureSupportedNotes
Cost Tracking✅Works with all supported models
Logging✅Works across all integrations
End-user Tracking✅
Streaming✅
Fallbacks✅Works between supported models
Loadbalancing✅Works between supported models
Guardrails✅Applies to input and output text (non-streaming only)
Supported ProvidersAll LiteLLM supported providersopenai, anthropic, bedrock, vertex_ai, gemini, azure, azure_ai, etc.

Usage​

LiteLLM Python SDK​

Non-streaming example​

Anthropic Example using LiteLLM Python SDK
import litellm
response = await litellm.anthropic.messages.acreate(
    messages=[{"role": "user", "content": "Hello, can you tell me a short joke?"}],
    api_key=api_key,
    model="anthropic/claude-3-haiku-20240307",
    max_tokens=100,
)

Streaming example​

Anthropic Streaming Example using LiteLLM Python SDK
import litellm
response = await litellm.anthropic.messages.acreate(
    messages=[{"role": "user", "content": "Hello, can you tell me a short joke?"}],
    api_key=api_key,
    model="anthropic/claude-3-haiku-20240307",
    max_tokens=100,
    stream=True,
)
async for chunk in response:
    print(chunk)

Example response:

{
  "content": [
    {
      "text": "Hi! this is a very short joke",
      "type": "text"
    }
  ],
  "id": "msg_013Zva2CMHLNnXjNJJKqJ2EF",
  "model": "claude-3-7-sonnet-20250219",
  "role": "assistant",
  "stop_reason": "end_turn",
  "stop_sequence": null,
  "type": "message",
  "usage": {
    "input_tokens": 2095,
    "output_tokens": 503,
    "cache_creation_input_tokens": 2095,
    "cache_read_input_tokens": 0
  }
}

LiteLLM Proxy Server​

  1. Setup config.yaml
model_list:
    - model_name: anthropic-claude
      litellm_params:
        model: claude-3-7-sonnet-latest
        api_key: os.environ/ANTHROPIC_API_KEY
  1. Start proxy
litellm --config /path/to/config.yaml
  1. Test it!
Anthropic Example using LiteLLM Proxy Server
import anthropic

# point anthropic sdk to litellm proxy 
client = anthropic.Anthropic(
    base_url="http://0.0.0.0:4000",
    api_key="sk-1234",
)

response = client.messages.create(
    messages=[{"role": "user", "content": "Hello, can you tell me a short joke?"}],
    model="anthropic-claude",
    max_tokens=100,
)

Request Format​

Request body will be in the Anthropic messages API format. litellm follows the Anthropic messages specification for this endpoint.

Example request body​

{
  "model": "claude-3-7-sonnet-20250219",
  "max_tokens": 1024,
  "messages": [
    {
      "role": "user",
      "content": "Hello, world"
    }
  ]
}

Required Fields​

  • model (string):
    The model identifier (e.g., "claude-3-7-sonnet-20250219").
  • max_tokens (integer):
    The maximum number of tokens to generate before stopping.
    Note: The model may stop before reaching this limit; value must be greater than 1.
  • messages (array of objects):
    An ordered list of conversational turns.
    Each message object must include:
    • role (enum: "user" or "assistant"):
      Specifies the speaker of the message.
    • content (string or array of content blocks):
      The text or content blocks (e.g., an array containing objects with a type such as "text") that form the message.
      Example equivalence: 
      {"role": "user", "content": "Hello, Claude"}
      is equivalent to: 
      {"role": "user", "content": [{"type": "text", "text": "Hello, Claude"}]}

Optional Fields​

  • metadata (object):
    Contains additional metadata about the request (e.g., user_id as an opaque identifier).
  • stop_sequences (array of strings):
    Custom sequences that, when encountered in the generated text, cause the model to stop.
  • stream (boolean):
    Indicates whether to stream the response using server-sent events.
  • system (string or array):
    A system prompt providing context or specific instructions to the model.
  • temperature (number):
    Controls randomness in the model's responses. Valid range: 0 < temperature < 1.
  • thinking (object):
    Configuration for enabling extended thinking. If enabled, it includes:
    • budget_tokens (integer):
      Minimum of 1024 tokens (and less than max_tokens).
    • type (enum):
      E.g., "enabled".
  • tool_choice (object):
    Instructs how the model should utilize any provided tools.
  • tools (array of objects):
    Definitions for tools available to the model. Each tool includes:
    • name (string):
      The tool's name.
    • description (string):
      A detailed description of the tool.
    • input_schema (object):
      A JSON schema describing the expected input format for the tool.
  • top_k (integer):
    Limits sampling to the top K options.
  • top_p (number):
    Enables nucleus sampling with a cumulative probability cutoff. Valid range: 0 < top_p < 1.

Response Format​

Responses will be in the Anthropic messages API format.

Example Response​

{
  "content": [
    {
      "text": "Hi! My name is Claude.",
      "type": "text"
    }
  ],
  "id": "msg_013Zva2CMHLNnXjNJJKqJ2EF",
  "model": "claude-3-7-sonnet-20250219",
  "role": "assistant",
  "stop_reason": "end_turn",
  "stop_sequence": null,
  "type": "message",
  "usage": {
    "input_tokens": 2095,
    "output_tokens": 503,
    "cache_creation_input_tokens": 2095,
    "cache_read_input_tokens": 0
  }
}

Response fields​

  • content (array of objects):
    Contains the generated content blocks from the model. Each block includes:

    • type (string):
      Indicates the type of content (e.g., "text", "tool_use", "thinking", or "redacted_thinking").
    • text (string):
      The generated text from the model.
      Note: Maximum length is 5,000,000 characters.
    • citations (array of objects or null):
      Optional field providing citation details. Each citation includes:
      • cited_text (string):
        The excerpt being cited.
      • document_index (integer):
        An index referencing the cited document.
      • document_title (string or null):
        The title of the cited document.
      • start_char_index (integer):
        The starting character index for the citation.
      • end_char_index (integer):
        The ending character index for the citation.
      • type (string):
        Typically "char_location".

  • id (string):
    A unique identifier for the response message.
    Note: The format and length of IDs may change over time.

  • model (string):
    Specifies the model that generated the response.

  • role (string):
    Indicates the role of the generated message. For responses, this is always "assistant".

  • stop_reason (string):
    Explains why the model stopped generating text. Possible values include:

    • "end_turn": The model reached a natural stopping point.
    • "max_tokens": The generation stopped because the maximum token limit was reached.
    • "stop_sequence": A custom stop sequence was encountered.
    • "tool_use": The model invoked one or more tools.

  • stop_sequence (string or null):
    Contains the specific stop sequence that caused the generation to halt, if applicable; otherwise, it is null.

  • type (string):
    Denotes the type of response object, which is always "message".

  • usage (object):
    Provides details on token usage for billing and rate limiting. This includes:

    • input_tokens (integer):
      Total number of input tokens processed.
    • output_tokens (integer):
      Total number of output tokens generated.
    • cache_creation_input_tokens (integer or null):
      Number of tokens used to create a cache entry.
    • cache_read_input_tokens (integer or null):
      Number of tokens read from the cache.