Reasoning

What is this?

Some models (OpenAI's o1, o3, and o4-mini, Anthropic's thinking variants) emit reasoning tokens — internal chain-of-thought traces that explain how the model is working toward its answer. CopilotKit surfaces these as first-class messages: when a REASONING_MESSAGE_* event arrives from the agent, the chat renders it inline so the user can follow the agent's thinking.

Reasoning isn't a custom-renderer plumb-in — it's a dedicated message type on the chat view. You can either accept the built-in rendering or override the reasoningMessage slot with your own component.

When should I use this?

Expose reasoning in the UI when you want to:

• Give users real-time insight into the agent's thought process
• Show progress on long or multi-step problems
• Debug prompt behavior during development
• Brand the reasoning card to match the rest of your product

Default reasoning rendering (zero-config)

Out of the box, reasoning events render inside CopilotKit's built-in CopilotChatReasoningMessage card:

• A "Thinking…" label with a pulsing indicator while the model reasons.
• Auto-expanded content so users can follow the chain of thought live.
• Collapses to "Thought for X seconds" once reasoning finishes, with a chevron to re-expand.
• Reasoning text rendered as Markdown.

No configuration is needed — if your model emits reasoning tokens, the card appears automatically:

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

Custom reasoning rendering

For full control over the reasoning card, pass a component to the reasoningMessage slot on messageView. Your component receives the ReasoningMessage object (.content holds the streaming text), the full messages list, and isRunning — enough to decide whether this block is still streaming and whether it's the active trailing message:

  return (
    <CopilotChat
      agentId="agentic-chat-reasoning"
      className="h-full rounded-2xl"
      messageView={{
        reasoningMessage: ReasoningBlock as typeof CopilotChatReasoningMessage,
      }}
    />
  );

The showcase's ReasoningBlock (imported 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.

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