Dynamic prompts with @dynamic_prompt and runtime context

TL;DR: v1 replaced callable prompts with the @dynamicprompt middleware decorator. Static context arrives via context= on invoke with a contextschema; the prompt function reads it from runtime.context.

The fix

Dynamic prompts

from dataclasses import dataclass
from langchain.agents import create_agent
from langchain.agents.middleware import dynamic_prompt, ModelRequest

@dataclass
class Context:
    user_role: str = "user"

@dynamic_prompt
def my_prompt(request: ModelRequest) -> str:
    base = "You are a helpful assistant."
    if request.runtime.context.user_role == "expert":
        return base + " Provide detailed technical responses."
    return base + " Explain concepts simply and avoid jargon."

agent = create_agent(
    model="gpt-5.5",
    tools=tools,
    middleware=[my_prompt],
    context_schema=Context,
)

agent.invoke(
    {"messages": [{"role": "user", "content": "Explain async programming"}]},
    context=Context(user_role="expert"),
)

Rules

• Do not pass a function as system_prompt. The v1 API takes a string there; dynamic behavior lives in middleware.
• context_schema types the context; context= on invoke/stream supplies it. This replaces stuffing values into config["configurable"].
• Keep the prompt function pure and fast: it runs before every model call. Expensive lookups belong in before_agent middleware or in tools.

When to use this

• This covers exactly what the title says: Dynamic prompts with @dynamic_prompt and runtime context.
• You are setting this up for the first time, or auditing an existing setup.
• You want the key gotchas in one place before you start.

When not to use this

• You are doing a different workflow with Dynamic; these steps are specific to the title above.
• You need the full reference docs; this is the short path, not the manual.

Compatibility

• Mentions 5.5 in the original; behavior may differ on much older or newer releases.

Workflow grounded in the official v1 migration guide (dynamic prompts), verified 2026-09-26. Migration: https://docs.langchain.com/oss/python/migrate/langchain-v1