where should I initialize the langfuse client which i need t LiveKit Community #ask-ai

where should I initialize the langfuse client whic...

numerous-receptionist-14192

12/18/2025, 2:02 PM

where should I initialize the langfuse client which i need to get my agent's system prompt? example code:

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server = AgentServer()

def prewarm(proc: JobProcess):
    ...

server.setup_fnc = prewarm

class MyAgent(Agent):
    def __init__(self) -> None:
        prompt = langfuse_client.get_prompt(PROMPT_NAME, fallback=PROMPT_FALLBACK).compile()
        super().__init__(instructions=prompt)

    async def on_enter(self) -> None:
        await self.session.say(text="Hello")

@server.rtc_session(agent_name=AGENT_NAME)
async def entrypoint(ctx: JobContext) -> None:
    # Connect to the LiveKit room, subscribing only to audio
    await ctx.connect(auto_subscribe=AutoSubscribe.AUDIO_ONLY)

    session: AgentSession = AgentSession(
        stt=...,
        llm=...,
        tts=...,
        vad=...,
    )

    await session.start(room=ctx.room, agent=MyAgent())

if __name__ == "__main__":
    cli.run_app(server)

tall-airline-16756

12/18/2025, 2:03 PM

Thanks for reaching out, Karl. I'm an AI assistant and I'm here to help. Give me a moment while I research this topic.

tall-airline-16756

12/18/2025, 2:03 PM

You're asking where to initialize the Langfuse client so

MyAgent.__init__

can call

langfuse_client.get_prompt(...)

. Initialize Langfuse inside the

@server.rtc_session

entrypoint, after connecting (

await ctx.connect(...)

) and before creating the

AgentSession

or instantiating

MyAgent

. Minimal example change:

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@server.rtc_session(agent_name=AGENT_NAME)
async def entrypoint(ctx: JobContext) -> None:
    await ctx.connect(auto_subscribe=AutoSubscribe.AUDIO_ONLY)

    # Initialize Langfuse here so it's available when MyAgent() runs
    langfuse_client = setup_langfuse()  # your Langfuse init function / config

    session: AgentSession = AgentSession(
        stt=...,
        llm=...,
        tts=...,
        vad=...,
    )

    await session.start(room=ctx.room, agent=MyAgent())

MyAgent

needs the client instance directly, pass it into the agent instead of relying on a global:

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class MyAgent(Agent):
    def __init__(self, lf_client):
        prompt = lf_client.get_prompt(PROMPT_NAME, fallback=PROMPT_FALLBACK).compile()
        super().__init__(instructions=prompt)

# then:
await session.start(room=ctx.room, agent=MyAgent(langfuse_client))

Would you like an example

setup_langfuse()

snippet for your environment or guidance on making

langfuse_client

safe for tests? Sources: Observability data hooks | LiveKit docs

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