add_usage

Example:

from langchain_core.messages.ai import add_usage

left = UsageMetadata(
    input_tokens=5,
    output_tokens=0,
    total_tokens=5,
    input_token_details=InputTokenDetails(cache_read=3),
)
right = UsageMetadata(
    input_tokens=0,
    output_tokens=10,
    total_tokens=10,
    output_token_details=OutputTokenDetails(reasoning=4),
)

add_usage(left, right)

results in

UsageMetadata(
    input_tokens=5,
    output_tokens=10,
    total_tokens=15,
    input_token_details=InputTokenDetails(cache_read=3),
    output_token_details=OutputTokenDetails(reasoning=4),
)

Args: left: The first UsageMetadata object. right: The second UsageMetadata object.