Reasoning Messages

"""Reasoning agent: emits AG-UI REASONING_MESSAGE_* events.Shared by reasoning-default (CopilotKit's built-in reasoning slot) andreasoning-custom (a custom amber ReasoningBlock).Why a reasoning model plus the Responses API: the OpenAI Responses API streams`response.reasoning_summary_text.delta` items only for native reasoning models(gpt-5, o3, o4-mini and friends). The Strands bridge translates those intoAG-UI REASONING_MESSAGE_* events with `role: "reasoning"`, which the frontendrenders through the `reasoningMessage` slot. gpt-4o emits no reasoning items, sothe showcase's default chat-completions model would never light the slot up.`summary: "detailed"` rather than `"auto"` is deliberate: with `"auto"` themodel decides, and it frequently skips the summary entirely, which leaves thereasoning slot unmounted. Override the model with `OPENAI_REASONING_MODEL`.Mirrors `langgraph-python/src/agents/reasoning_agent.py`."""from __future__ import annotationsimport osfrom strands import Agentfrom ag_ui_strands import StrandsAgentSYSTEM_PROMPT = (    "You are a helpful assistant. For each user question, first think "    "step-by-step about the approach, then give a concise answer.")DEFAULT_REASONING_MODEL = "gpt-5.4"def reasoning_model_id() -> str:    """Resolve the reasoning model at call time.    Read here rather than at module scope: the agent server imports this module    before it calls `load_dotenv()`, so a module-level read would always miss an    `OPENAI_REASONING_MODEL` set in `.env`.    """    return os.environ.get("OPENAI_REASONING_MODEL", DEFAULT_REASONING_MODEL)def build_reasoning_model():    """Construct the Responses-API model that streams reasoning summaries.    `OpenAIResponsesModel` is imported here rather than at module scope so the    dependency shows up where it is used; it needs openai>=2, which the pinned    requirements provide. The agent server builds these agents at import time,    so an older install still fails the whole server, not just these demos.    """    from strands.models.openai_responses import OpenAIResponsesModel    api_key = os.getenv("OPENAI_API_KEY", "")    if not api_key:        raise RuntimeError("OPENAI_API_KEY must be set for the strands showcase agent")    return OpenAIResponsesModel(        client_args={"api_key": api_key},        model_id=reasoning_model_id(),        params={"reasoning": {"effort": "medium", "summary": "detailed"}},    )def build_reasoning_agent() -> StrandsAgent:    """Construct the tool-free StrandsAgent backing both reasoning demos."""    strands_agent = Agent(        model=build_reasoning_model(),        system_prompt=SYSTEM_PROMPT,        tools=[],    )    return StrandsAgent(        agent=strands_agent,        name="reasoning",        description="Strands agent that streams reasoning summaries alongside its answer",    )

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

const AGENT_ID = "reasoning-default";export default function ReasoningDefaultDemo() {  return (    <CopilotKit runtimeUrl="/api/copilotkit" agent={AGENT_ID}>      <div className="flex justify-center items-center h-screen w-full">        <div className="h-full w-full max-w-4xl">          <Chat />        </div>      </div>    </CopilotKit>  );}function Chat() {  useReasoningDefaultSuggestions();  return <CopilotChat agentId={AGENT_ID} 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: emits AG-UI REASONING_MESSAGE_* events.Shared by reasoning-default (CopilotKit's built-in reasoning slot) andreasoning-custom (a custom amber ReasoningBlock).Why a reasoning model plus the Responses API: the OpenAI Responses API streams`response.reasoning_summary_text.delta` items only for native reasoning models(gpt-5, o3, o4-mini and friends). The Strands bridge translates those intoAG-UI REASONING_MESSAGE_* events with `role: "reasoning"`, which the frontendrenders through the `reasoningMessage` slot. gpt-4o emits no reasoning items, sothe showcase's default chat-completions model would never light the slot up.`summary: "detailed"` rather than `"auto"` is deliberate: with `"auto"` themodel decides, and it frequently skips the summary entirely, which leaves thereasoning slot unmounted. Override the model with `OPENAI_REASONING_MODEL`.Mirrors `langgraph-python/src/agents/reasoning_agent.py`."""from __future__ import annotationsimport osfrom strands import Agentfrom ag_ui_strands import StrandsAgentSYSTEM_PROMPT = (    "You are a helpful assistant. For each user question, first think "    "step-by-step about the approach, then give a concise answer.")DEFAULT_REASONING_MODEL = "gpt-5.4"def reasoning_model_id() -> str:    """Resolve the reasoning model at call time.    Read here rather than at module scope: the agent server imports this module    before it calls `load_dotenv()`, so a module-level read would always miss an    `OPENAI_REASONING_MODEL` set in `.env`.    """    return os.environ.get("OPENAI_REASONING_MODEL", DEFAULT_REASONING_MODEL)def build_reasoning_model():    """Construct the Responses-API model that streams reasoning summaries.    `OpenAIResponsesModel` is imported here rather than at module scope so the    dependency shows up where it is used; it needs openai>=2, which the pinned    requirements provide. The agent server builds these agents at import time,    so an older install still fails the whole server, not just these demos.    """    from strands.models.openai_responses import OpenAIResponsesModel    api_key = os.getenv("OPENAI_API_KEY", "")    if not api_key:        raise RuntimeError("OPENAI_API_KEY must be set for the strands showcase agent")    return OpenAIResponsesModel(        client_args={"api_key": api_key},        model_id=reasoning_model_id(),        params={"reasoning": {"effort": "medium", "summary": "detailed"}},    )def build_reasoning_agent() -> StrandsAgent:    """Construct the tool-free StrandsAgent backing both reasoning demos."""    strands_agent = Agent(        model=build_reasoning_model(),        system_prompt=SYSTEM_PROMPT,        tools=[],    )    return StrandsAgent(        agent=strands_agent,        name="reasoning",        description="Strands agent that streams reasoning summaries alongside its answer",    )

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

const AGENT_ID = "reasoning-custom";export default function ReasoningCustomDemo() {  return (    <CopilotKit runtimeUrl="/api/copilotkit" agent={AGENT_ID}>      <div className="flex justify-center items-center h-screen w-full">        <div className="h-full w-full max-w-4xl">          <Chat />        </div>      </div>    </CopilotKit>  );}function Chat() {  useReasoningCustomSuggestions();  return (    <CopilotChat      agentId={AGENT_ID}      className="h-full rounded-2xl"      messageView={{        reasoningMessage:          ReasoningBlock as unknown 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