Some time around October 15 system messages and variable data sent over the create chat endpoint have become completely ignored or at best very unreliable between turns in a conversation. Very easy to re-produce with just 2 messages. The system message remains in the chat messages history yet is ignored completely. Likewise the liquid js variables which may inject that data into the main prompt are also ignored. Create a new chat:

{
  "assistantId": "92ff7248-0468-423e-a2b5-9e549bb45d3f",
  "input": [
    {
      "role": "system",
      "content": "You are in a chat session with a user named Bob"
    },
    {
      "role": "user",
      "content": "Hi, I need help!"
    }
  ],
  "assistantOverrides": {
    "variableValues": {
      "firstName": "Bob",
      "lastName": "McTester"
    }
  },
  "stream": false
}

Then create a follow up chat:

{
  "assistantId": "92ff7248-0468-423e-a2b5-9e549bb45d3f",
  "previousChatId": "a5bd1686-b98f-41e9-a447-0c9f40c35058",
  "input": "First, please confirm that you know my first name?",
  "stream": false
}

Response:

...    "output": [
        {
            "role": "assistant",
            "content": "Your first name is Angela. Is that correct?"
        }
    ],

This worked reliably for thousands of chats over the last month and is now un-usable. I see no updates in your changelog since September.

To ensure system messages and variable data are recognized in follow-up chats, always include them in each request—even when using

previousChatId

. Here’s an example of a follow-up request:

json
{
  "assistantId": "92ff7248-0468-423e-a2b5-9e549bb45d3f",
  "previousChatId": "a5bd1686-b98f-41e9-a447-0c9f40c35058",
  "input": [
    { "role": "system", "content": "You are in a chat session with a user named Bob" },
    { "role": "user", "content": "First, please confirm that you know my first name?" }
  ],
  "assistantOverrides": {
    "variableValues": {
      "firstName": "Bob",
      "lastName": "McTester"
    }
  },
  "stream": false
}

This should restore the expected context between turns. For more, see the [Vapi chat API reference](https://docs.vapi.ai/api-reference/chats/create?explorer=true). Source: - [Vapi API Reference: Create Chat](https://docs.vapi.ai/api-reference/chats/create?explorer=true)

although that would make sense unfortunately does not work either

{
  "id": "ba755229-e26f-455f-a516-187675c5537d",
  "orgId": "11111111111111111111111111111",
  "previousChatId": "ec183bb7-040e-416c-adcc-9793664c8a9d",
  "assistantId": "92ff7248-0468-423e-a2b5-9e549bb45d3f",
  "input": [
    {
      "role": "system",
      "content": "You are in a chat session with a user named Bob"
    },
    {
      "role": "user",
      "content": "First, can you please confirm my first name?"
    }
  ],
  "output": [
    {
      "role": "assistant",
      "content": "Sure! Your first name is listed as Alex. Can you please confirm if that's correct?"
    }
  ],
  "messages": [
    {
      "role": "system",
      "content": "You are in a chat session with a user named Bob"
    },
    {
      "role": "user",
      "content": "Hi, I need help!"
    },
    {
      "role": "assistant",
      "content": "Hi! I'd be more than happy to help you. Let's get started with your interview. What's your first name, so I can greet you properly?"
    }
  ]
}