anthropic: stream token usage (#20180)

open to other ideas
<img width="1181" alt="Screenshot 2024-04-08 at 5 34 08 PM"
src="https://github.com/langchain-ai/langchain/assets/22008038/03eb11c4-5eb5-43e3-9109-a13f76098fa4">

---------

Co-authored-by: Chester Curme <chester.curme@gmail.com>

libs/partners/anthropic/langchain_anthropic/chat_models.py

@@ -43,6 +43,7 @@ from langchain_core.messages import (
     ToolCall,
     ToolMessage,
 )
+from langchain_core.messages.ai import UsageMetadata
 from langchain_core.outputs import ChatGeneration, ChatGenerationChunk, ChatResult
 from langchain_core.pydantic_v1 import BaseModel, Field, SecretStr, root_validator
 from langchain_core.runnables import (
@@ -653,14 +654,20 @@ class ChatAnthropic(BaseChatModel):
                 message_chunk = AIMessageChunk(
                     content=message.content,
                     tool_call_chunks=tool_call_chunks,  # type: ignore[arg-type]
+                    usage_metadata=message.usage_metadata,
                 )
                 yield ChatGenerationChunk(message=message_chunk)
             else:
                 yield cast(ChatGenerationChunk, result.generations[0])
             return
+        full_generation_info: dict = {}
         with self._client.messages.stream(**params) as stream:
             for text in stream.text_stream:
-                chunk = ChatGenerationChunk(message=AIMessageChunk(content=text))
+                chunk, full_generation_info = _make_chat_generation_chunk(
+                    text,
+                    stream.current_message_snapshot.model_dump(),
+                    full_generation_info,
+                )
                 if run_manager:
                     run_manager.on_llm_new_token(text, chunk=chunk)
                 yield chunk
@@ -692,14 +699,20 @@ class ChatAnthropic(BaseChatModel):
                 message_chunk = AIMessageChunk(
                     content=message.content,
                     tool_call_chunks=tool_call_chunks,  # type: ignore[arg-type]
+                    usage_metadata=message.usage_metadata,
                 )
                 yield ChatGenerationChunk(message=message_chunk)
             else:
                 yield cast(ChatGenerationChunk, result.generations[0])
             return
+        full_generation_info: dict = {}
         async with self._async_client.messages.stream(**params) as stream:
             async for text in stream.text_stream:
-                chunk = ChatGenerationChunk(message=AIMessageChunk(content=text))
+                chunk, full_generation_info = _make_chat_generation_chunk(
+                    text,
+                    stream.current_message_snapshot.model_dump(),
+                    full_generation_info,
+                )
                 if run_manager:
                     await run_manager.on_llm_new_token(text, chunk=chunk)
                 yield chunk
@@ -1064,6 +1077,59 @@ def _lc_tool_calls_to_anthropic_tool_use_blocks(
     return blocks
 
 
+def _make_chat_generation_chunk(
+    text: str, message_dump: dict, full_generation_info: dict
+) -> Tuple[ChatGenerationChunk, dict]:
+    """Collect metadata and make ChatGenerationChunk.
+
+    Args:
+        text: text of the message chunk
+        message_dump: dict with metadata of the message chunk
+        full_generation_info: dict collecting metadata for full stream
+
+    Returns:
+        Tuple with ChatGenerationChunk and updated full_generation_info
+    """
+    generation_info = {}
+    usage_metadata: Optional[UsageMetadata] = None
+    for k, v in message_dump.items():
+        if k in ("content", "role", "type") or (
+            k in full_generation_info and k not in ("usage", "stop_reason")
+        ):
+            continue
+        elif k == "usage":
+            input_tokens = v.get("input_tokens", 0)
+            output_tokens = v.get("output_tokens", 0)
+            if "usage" not in full_generation_info:
+                full_generation_info[k] = v
+                usage_metadata = UsageMetadata(
+                    input_tokens=input_tokens,
+                    output_tokens=output_tokens,
+                    total_tokens=input_tokens + output_tokens,
+                )
+            else:
+                seen_input_tokens = full_generation_info[k].get("input_tokens", 0)
+                # Anthropic returns the same input token count for each message in a
+                # stream. To avoid double counting, we only count the input tokens
+                # once. After that, we set the input tokens to zero.
+                new_input_tokens = 0 if seen_input_tokens else input_tokens
+                usage_metadata = UsageMetadata(
+                    input_tokens=new_input_tokens,
+                    output_tokens=output_tokens,
+                    total_tokens=new_input_tokens + output_tokens,
+                )
+        else:
+            full_generation_info[k] = v
+            generation_info[k] = v
+    return (
+        ChatGenerationChunk(
+            message=AIMessageChunk(content=text, usage_metadata=usage_metadata),
+            generation_info=generation_info,
+        ),
+        full_generation_info,
+    )
+
+
 @deprecated(since="0.1.0", removal="0.3.0", alternative="ChatAnthropic")
 class ChatAnthropicMessages(ChatAnthropic):
     pass