Reasoning Messages

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:

<Snippet cell="reasoning-default-render" region="default-reasoning-zero-config" title="frontend/src/app/page.tsx — default reasoning" />

Customizing the Reasoning Message

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

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:

import { CopilotChat } from "@copilotkit/react-core/v2";
import "@copilotkit/react-ui/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:

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:

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:

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-ui";
import { CopilotChat } from "@copilotkit/react-core/v2";
import "@copilotkit/react-ui/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: