get_usage_metadata_callback

Example:

from langchain.chat_models import init_chat_model
from langchain_core.callbacks import get_usage_metadata_callback

llm_1 = init_chat_model(model="openai:gpt-4o-mini")
llm_2 = init_chat_model(model="anthropic:claude-haiku-4-5-20251001")

with get_usage_metadata_callback() as cb:
    llm_1.invoke("Hello")
    llm_2.invoke("Hello")
    print(cb.usage_metadata)

{
    "gpt-4o-mini-2024-07-18": {
        "input_tokens": 8,
        "output_tokens": 10,
        "total_tokens": 18,
        "input_token_details": {"audio": 0, "cache_read": 0},
        "output_token_details": {"audio": 0, "reasoning": 0},
    },
    "claude-haiku-4-5-20251001": {
        "input_tokens": 8,
        "output_tokens": 21,
        "total_tokens": 29,
        "input_token_details": {"cache_read": 0, "cache_creation": 0},
    },
}