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Recommended ReadingBefore diving into this content, it might be helpful to read the following:
Many LLM applications have a chatbot-like interface in which the user and the LLM application engage in a multi-turn conversation. In order to track these conversations, you can use the Threads feature in LangSmith.

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Group traces into threads

A Thread is a sequence of traces representing a single conversation. Each response is represented as its own trace, but these traces are linked together by being part of the same thread. To associate traces together, you need to pass in a special metadata key where the value is the unique identifier for that thread. The key value is the unique identifier for that conversation. The key name should be one of:
  • session_id
  • thread_id
  • conversation_id.
The value can be any string you want, but we recommend using UUIDs, such as f47ac10b-58cc-4372-a567-0e02b2c3d479.

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Code example

This example demonstrates how to log and retrieve conversation history from LangSmith to maintain long-running chats. You can add metadata to your traces in LangSmith in a variety of ways, this code will show how to do so dynamically, but read the previously linked guide to learn about all the ways you can add thread identifier metadata to your traces. 
import openai
from langsmith import traceable
from langsmith import Client
import langsmith as ls
from langsmith.wrappers import wrap_openai

client = wrap_openai(openai.Client())
langsmith_client = Client()

# Config used for this example
langsmith_project = "project-with-threads"

session_id = "thread-id-1"

langsmith_extra={"project_name": langsmith_project, "metadata":{"session_id": session_id}}

# gets a history of all LLM calls in the thread to construct conversation history
def get_thread_history(thread_id: str, project_name: str):
    # Filter runs by the specific thread and project
    filter_string = f'and(in(metadata_key, ["session_id","conversation_id","thread_id"]), eq(metadata_value, "{thread_id}"))'
    # Only grab the LLM runs
    runs = [r for r in langsmith_client.list_runs(project_name=project_name, filter=filter_string, run_type="llm")]

    # Sort by start time to get the most recent interaction
    runs = sorted(runs, key=lambda run: run.start_time, reverse=True)
    # The current state of the conversation
    return runs[0].inputs['messages'] + [runs[0].outputs['choices'][0]['message']]

# if an existing conversation is continued, this function looks up the current run's metadata to get the session_id, calls get_thread_history, and appends the new user question before making a call to the chat model
@traceable(name="Chat Bot")
def chat_pipeline(question: str, get_chat_history: bool = False):
    # Whether to continue an existing thread or start a new one
    if get_chat_history:
        run_tree = ls.get_current_run_tree()
        messages = get_thread_history(run_tree.extra["metadata"]["session_id"],run_tree.session_name) + [{"role": "user", "content": question}]
    else:
        messages = [{"role": "user", "content": question}]

    # Invoke the model
    chat_completion = client.chat.completions.create(
        model="gpt-4o-mini", messages=messages
    )
    return chat_completion.choices[0].message.content

# Start the conversation
chat_pipeline("Hi, my name is Bob", langsmith_extra=langsmith_extra)
After waiting a few seconds, you can make the following calls to continue the conversation. By passing getChatHistory: true, you can continue the conversation from where it left off. This means that the LLM will receive the entire message history and respond to it, instead of just responding to the latest message. 
# Continue the conversation (WAIT A FEW SECONDS BEFORE RUNNING THIS SO THE FIRST TRACE CAN BE INGESTED)
chat_pipeline("What is my name?", get_chat_history=True, langsmith_extra=langsmith_extra)

# Keep the conversation going (WAIT A FEW SECONDS BEFORE RUNNING THIS SO THE PREVIOUS TRACE CAN BE INGESTED)
chat_pipeline("What was the first message I sent you", get_chat_history=True, langsmith_extra=langsmith_extra)

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View threads

You can view threads by clicking on the Threads tab in any project details page. You will then see a list of all threads, sorted by the most recent activity. Thread Tab You can then click into a particular thread. This will open the history for a particular thread. If your threads are formatted as chat messages, you will a chatbot-like UI where you can see a history of inputs and outputs. Conversation You can open up the trace or annotate the trace in a side panel by clicking on Annotate and Open trace, respectively.