add an Anthropic Token Usage callback

[Kevin-McIsaac]

Checked

• I searched existing ideas and did not find a similar one
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Feature request

Enable access to the token count and usage cost for Anthropic LLM by adding a call back handler to langchain_community.callbacks.

Motivation

Track usage costs for Claude 3

Proposal (If applicable)

The existing OpenAI callback (openai_callback) returns the token count, but not the cost, when used with Claude. The cost is not returned because the Anthropic model names are not in the unit cost dict.

The simplest solution would be to create a new callback for Anthropic based on the OpenAI callback and add a different cost table.

from langchain_anthropic import ChatAnthropic
from langchain_community.callbacks.manager import get_openai_callback

llm = ChatAnthropic(model="claude-3-haiku-20240307", temperature=0, stream_usage=True,)

with get_openai_callback() as cb:
    result = llm.invoke("hello, what is your name.")
    print(cb)

# Tokens Used: 29
# 	Prompt Tokens: 14
# 	Completion Tokens: 15
# Successful Requests: 1
# Total Cost (USD): $0.0