Reasoning Messages

Customize how reasoning (thinking) tokens from models like o1, o3, and o4-mini are displayed.

"""Reasoning agent for LlamaIndex.Shared by `agentic-chat-reasoning` (custom amber ReasoningBlock slot) and`reasoning-default-render` (CopilotKit's built-in reasoning slot). The agentis built on the same shared `get_ag_ui_workflow_router` used by the rest ofthe package. The system prompt asks the model to think step-by-step beforeanswering, so the LLM produces reasoning-style prose that the chat UI canrender.Note: `llama-index-protocols-ag-ui` streams chat deltas as assistant text. Ifthe underlying OpenAI model emits reasoning tokens via the responses API,they will surface as REASONING_MESSAGE_* events; otherwise the reasoningshows up as the first part of the assistant message. Either way the frontend`CopilotChatReasoningMessage` slot composes with the flow — no custom backendplumbing is needed for the happy path."""from __future__ import annotationsimport osfrom llama_index.llms.openai import OpenAIfrom llama_index.protocols.ag_ui.router import get_ag_ui_workflow_routerSYSTEM_PROMPT = (    "You are a helpful assistant. For each user question, first think "    "step-by-step about the approach, then give a concise answer. Keep "    "responses brief -- 1 to 3 sentences max.")_openai_kwargs = {}if os.environ.get("OPENAI_BASE_URL"):    _openai_kwargs["api_base"] = os.environ["OPENAI_BASE_URL"]reasoning_router = get_ag_ui_workflow_router(    llm=OpenAI(model="gpt-4.1", **_openai_kwargs),    frontend_tools=[],    backend_tools=[],    system_prompt=SYSTEM_PROMPT,    initial_state={},)

Some models (like OpenAI's o1, o3, and o4-mini) emit reasoning tokens: internal "thinking" traces that show the model's chain-of-thought before it produces a final answer. CopilotKit surfaces these tokens automatically with a collapsible Reasoning Message card.

Default Behavior#

When reasoning events arrive from the agent, CopilotKit renders them inside a built-in card that:

Shows a "Thinking…" label with a pulsating indicator while the model is reasoning.
Expands automatically so you can follow the model's thought process in real-time.
Collapses and switches to "Thought for X seconds" once reasoning finishes.
Renders the reasoning content as Markdown.
Includes a chevron toggle so users can re-expand and review the reasoning at any time.

No extra configuration is needed; if your model emits reasoning tokens, the card appears automatically.

The only requirement is connecting your agent to CopilotKit; no extra props or configuration needed:

page.tsx

          <CopilotChat            agentId="reasoning-default-render"            className="h-full rounded-2xl"          />

Customizing the Reasoning Message#

The reasoning message is composed of three sub-components that can each be replaced independently via slot props:

Sub-component	Slot prop	Description
`Header`	`header`	The clickable bar with the brain icon, label, and chevron
`Content`	`contentView`	The reasoning text area (Markdown)
`Toggle`	`toggle`	The expand/collapse animation wrapper

You pass custom sub-components through the messageView prop on CopilotChat, CopilotPopup, or CopilotSidebar:

<CopilotChat
  messageView={{
    reasoningMessage: {
      header: CustomHeader,
      contentView: CustomContent,
    },
  }}
/>

Custom Header#

Replace the header to change the icon, label text, or styling. The header receives these props:

Prop	Type	Description
`isOpen`	`boolean`	Whether the content panel is currently expanded
`label`	`string`	`"Thinking…"` while streaming, `"Thought for X seconds"` after
`hasContent`	`boolean`	Whether any reasoning text has been received
`isStreaming`	`boolean`	Whether reasoning is actively streaming
`onClick`	`() => void`	Toggle handler (only present when `hasContent` is `true`)

import { CopilotChat } from "@copilotkit/react-core/v2";
import "@copilotkit/react-core/v2/styles.css";

function CustomHeader({
  isOpen,
  label,
  hasContent,
  isStreaming,
  ...props
}: React.ButtonHTMLAttributes<HTMLButtonElement> & {
  isOpen?: boolean;
  label?: string;
  hasContent?: boolean;
  isStreaming?: boolean;
}) {
  return (
    <button
      className="flex w-full items-center gap-2 px-3 py-2 text-sm font-medium"
      {...props}
    >
      {isStreaming ? "🧠" : "💡"}
      <span>{label}</span>
      {hasContent && (
        <span className="ml-auto text-xs">{isOpen ? "Hide" : "Show"}</span>
      )}
    </button>
  );
}

<CopilotChat
  messageView={{
    reasoningMessage: { header: CustomHeader },
  }}
/>

Custom Content#

Replace the content area to change how reasoning text is displayed:

Prop	Type	Description
`isStreaming`	`boolean`	Whether reasoning tokens are still arriving
`hasContent`	`boolean`	Whether any reasoning text has been received
`children`	`string`	The raw reasoning text

function CustomContent({
  isStreaming,
  hasContent,
  children,
  ...props
}: React.HTMLAttributes<HTMLDivElement> & {
  isStreaming?: boolean;
  hasContent?: boolean;
}) {
  if (!hasContent && !isStreaming) return null;

  return (
    <div className="px-4 pb-3 text-sm text-gray-500 font-mono" {...props}>
      {children}
      {isStreaming && <span className="animate-pulse ml-1">▊</span>}
    </div>
  );
}

<CopilotChat
  messageView={{
    reasoningMessage: { contentView: CustomContent },
  }}
/>

Fully Custom Reasoning Message#

For complete control over the entire reasoning card, pass a component instead of slot props. Your component receives the same top-level props as the built-in one:

Prop	Type	Description
`message`	`ReasoningMessage`	The reasoning message object (`.content` holds the text)
`messages`	`Message[]`	All messages in the conversation
`isRunning`	`boolean`	Whether the agent is currently running

"""Reasoning agent for LlamaIndex.Shared by `agentic-chat-reasoning` (custom amber ReasoningBlock slot) and`reasoning-default-render` (CopilotKit's built-in reasoning slot). The agentis built on the same shared `get_ag_ui_workflow_router` used by the rest ofthe package. The system prompt asks the model to think step-by-step beforeanswering, so the LLM produces reasoning-style prose that the chat UI canrender.Note: `llama-index-protocols-ag-ui` streams chat deltas as assistant text. Ifthe underlying OpenAI model emits reasoning tokens via the responses API,they will surface as REASONING_MESSAGE_* events; otherwise the reasoningshows up as the first part of the assistant message. Either way the frontend`CopilotChatReasoningMessage` slot composes with the flow — no custom backendplumbing is needed for the happy path."""from __future__ import annotationsimport osfrom llama_index.llms.openai import OpenAIfrom llama_index.protocols.ag_ui.router import get_ag_ui_workflow_routerSYSTEM_PROMPT = (    "You are a helpful assistant. For each user question, first think "    "step-by-step about the approach, then give a concise answer. Keep "    "responses brief -- 1 to 3 sentences max.")_openai_kwargs = {}if os.environ.get("OPENAI_BASE_URL"):    _openai_kwargs["api_base"] = os.environ["OPENAI_BASE_URL"]reasoning_router = get_ag_ui_workflow_router(    llm=OpenAI(model="gpt-4.1", **_openai_kwargs),    frontend_tools=[],    backend_tools=[],    system_prompt=SYSTEM_PROMPT,    initial_state={},)

The ReasoningBlock used above renders the reasoning as an amber-tagged inline banner, intentionally louder than the default card so the thinking chain is the focal UI of the demo. Swap in your own component to match your product's tone:

page.tsx

import React from "react";import {  CopilotChat,  CopilotChatReasoningMessage,} from "@copilotkit/react-core/v2";import { CopilotKit } from "@copilotkit/react-core";import { ReasoningBlock } from "./reasoning-block";// Outer layer — provider + layout chrome.export default function AgenticChatReasoningDemo() {  return (    <CopilotKit runtimeUrl="/api/copilotkit" agent="agentic-chat-reasoning">      <div className="flex justify-center items-center h-screen w-full">        <div className="h-full w-full max-w-4xl">          <Chat />        </div>      </div>    </CopilotKit>  );}// Inner — wires a custom `reasoningMessage` slot that makes the thinking// chain visually prominent, then renders the chat.function Chat() {  return (    <CopilotChat      agentId="agentic-chat-reasoning"      className="h-full rounded-2xl"      messageView={{        reasoningMessage: ReasoningBlock as typeof CopilotChatReasoningMessage,      }}    />  );}

Render-Prop Children#

The built-in CopilotChatReasoningMessage also supports a render-prop pattern for cases where you want to rearrange the built-in sub-components without reimplementing them:

import {
  CopilotChatReasoningMessage,
} from "@copilotkit/react-core/v2";
import { CopilotChat } from "@copilotkit/react-core/v2";
import "@copilotkit/react-core/v2/styles.css";

function MyReasoningLayout(props: React.ComponentProps<typeof CopilotChatReasoningMessage>) {
  return (
    <CopilotChatReasoningMessage {...props}>
      {({ header, toggle }) => (
        <div className="rounded-lg border bg-yellow-50 my-2">
          {header}
          {toggle}
        </div>
      )}
    </CopilotChatReasoningMessage>
  );
}

<CopilotChat
  messageView={{
    reasoningMessage: MyReasoningLayout,
  }}
/>

The render-prop callback receives:

Property	Description
`header`	Pre-rendered header element
`contentView`	Pre-rendered content element
`toggle`	Pre-rendered expand/collapse wrapper (contains `contentView`)
`message`	The reasoning message object
`messages`	All messages
`isRunning`	Whether the agent is running