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Conversation flow replaces multi-prompt agents

Retell is retiring multi-prompt agents. From 12/15/2026 you can’t create a new multi-prompt agent, and from 02/01/2027 you can’t edit one. After that, Retell converts the remaining multi-prompt agents to conversation flow agents. Single prompt and conversation flow agents aren’t affected. Migrate your multi-prompt agents well ahead of these dates. While the multi-prompt agent still handles your calls, you have time to test its replacement, move phone numbers and code to it, and fix anything that behaves differently, with no deadline forcing changes onto live calls. A multi-prompt agent splits a call into LLM states and moves between them through tool calls. Conversation flow covers the same design: each state becomes a subagent node with its own prompt and tools. Conversation flow also has node types that multi-prompt agents never had, such as logic split and code nodes. An agent is a multi-prompt agent when its response engine is a Retell LLM with at least one entry in states. A Retell LLM without states, or with states: [], is a single prompt LLM and isn’t affected. Affected APIs: Use instead: a conversation flow agent, or a single prompt agent if one prompt can cover the whole call. Single prompt vs. conversation flow helps you choose. What’s changing on 12/15/2026:
  1. The dashboard stops offering Multi-Prompt Agent (Legacy) when you create an agent, and you can no longer duplicate or import a multi-prompt agent.
  2. The API rejects any request that would create a new multi-prompt agent:
    • Create Retell LLM with a non-empty states array.
    • Update Retell LLM that adds states to a Retell LLM that has none.
    • Create Agent or Create Chat Agent with a response_engine that points to a multi-prompt Retell LLM, and Update Agent or Update Chat Agent that switches an agent to one.
  3. Existing multi-prompt agents keep running. Until 02/01/2027 you can still edit them, create versions, and publish them.
What’s changing on 02/01/2027:
  1. You can no longer edit multi-prompt agents. Update Retell LLM requests on a multi-prompt LLM fail, and you can’t change a multi-prompt agent’s prompts, states, or tools on the dashboard.
  2. Existing multi-prompt agents keep handling calls.
After 02/01/2027: Retell converts the remaining multi-prompt agents to conversation flow agents. A converted agent’s response engine is a conversation flow, so code that reads or updates its Retell LLM has to use the conversation flow APIs, such as Update Conversation Flow, instead. A conversation flow moves between nodes with transition conditions, not the tool calls that move a multi-prompt agent between states, so a converted agent can behave differently on the same call. Migrating yourself lets you test that behavior before your callers hear it.
The conversion changes your agents but not your code. If your code creates multi-prompt agents, change it before 12/15/2026. If your code calls Update Retell LLM on a multi-prompt agent, for example to change prompts before each campaign, those calls fail from 02/01/2027. Start these code changes now, so you can test them before the date that breaks the old code.
Migration:
  1. Find your multi-prompt agents. On the dashboard, the Agents list shows Multi-Prompt as the agent type. Through the API, call Get Retell LLM for each agent whose response_engine.type is retell-llm, and check whether states has entries.
  2. Decide whether the agent needs a conversation flow. If one prompt can describe the whole call, a single prompt agent is less work to maintain. Otherwise, convert it to a conversation flow.
  3. To convert on the dashboard, open the agent, click More options (⋯) at the top of the agent page, and choose Convert to Conversational Flow. Conductor builds a new conversation flow agent from the multi-prompt agent and lists anything it couldn’t map. Review that list before you go on.
  4. If your edges pass values between states through parameters, collect those values with an extract dynamic variable node.
  5. Test the new agent with simulation testing or the LLM playground.
  6. Move your traffic. A dashboard conversion creates a new agent with a new agent ID, so assign it to your phone numbers and update any code, batch calls, or transfer settings that use the old agent ID.
  7. Update code that creates or edits multi-prompt agents. Build a conversation flow with Create Conversation Flow using the field mapping below.
Effective dates: From 12/15/2026, neither the dashboard nor the API creates new multi-prompt agents. From 02/01/2027 you can’t edit them, though they keep handling calls. After that, Retell converts the remaining ones to conversation flow agents.