Working with Items - OpenRouter SDK

The Items Paradigm

callModel is built on OpenRouter’s Responses API which uses an items-based model rather than the messages-based model used by OpenAI Chat or Vercel AI SDK. The key insight: items are emitted multiple times with the same ID but progressively updated content. You replace the entire item by ID rather than accumulating stream chunks.

Messages vs Items

Traditional (OpenAI Chat, Vercel AI)	callModel (Items-native)
Stream chunks, accumulate text	Stream items, replace by ID
Single message type	Multiple item types
Reconstruct content at end	Each emission is complete
Manual state management	Natural React state updates

Item Types

getItemsStream() yields these item types:

Type	Description
`message`	Assistant text responses
`function_call`	Tool invocations with arguments
`reasoning`	Model thinking (extended thinking)
`web_search_call`	Web search operations
`file_search_call`	File search operations
`image_generation_call`	Image generation operations
`function_call_output`	Results from executed tools

How Streaming Works

Each iteration yields a complete item with the same ID but updated content:

// Iteration 1
{
  id: "msg_123",
  type: "message",
  content: [{ type: "output_text", text: "Hello" }]
}

// Iteration 2
{
  id: "msg_123",
  type: "message",
  content: [{ type: "output_text", text: "Hello world" }]
}

// Iteration 3
{
  id: "msg_123",
  type: "message",
  content: [{ type: "output_text", text: "Hello world!" }]
}

The same pattern applies to function calls:

// Iteration 1
{ type: "function_call", callId: "call_456", arguments: "{\"q" }

// Iteration 2
{
  type: "function_call",
  callId: "call_456",
  arguments: "{\"query\": \"weather"
}

// Iteration 3
{
  type: "function_call",
  callId: "call_456",
  arguments: "{\"query\": \"weather in Paris\"}"
}

React Integration

The items paradigm eliminates manual chunk accumulation. Use a Map keyed by item ID and let React’s reconciliation handle updates:

import { useState } from 'react';
import type { StreamableOutputItem } from '@openrouter/agent';
import { OpenRouter } from '@openrouter/agent';

const client = new OpenRouter({ apiKey: process.env.OPENROUTER_API_KEY });

function Chat() {
  const [items, setItems] = useState<Map<string, StreamableOutputItem>>(
    new Map()
  );

  async function handleSubmit(input: string) {
    const result = client.callModel({
      model: 'anthropic/claude-sonnet-4',
      input,
    });

    for await (const item of result.getItemsStream()) {
      // Replace the entire item by ID - React re-renders automatically
      setItems((prev) => new Map(prev).set(item.id, item));
    }
  }

  return (
    <div>
      <form onSubmit={(e) => { e.preventDefault(); handleSubmit(input); }}>
        {/* input field */}
      </form>
      <div>
        {[...items.values()].map((item) => (
          <ItemRenderer key={item.id} item={item} />
        ))}
      </div>
    </div>
  );
}

function ItemRenderer({ item }: { item: StreamableOutputItem }) {
  switch (item.type) {
    case 'message':
      return <MessageItem message={item} />;
    case 'function_call':
      return <ToolCallItem call={item} />;
    case 'reasoning':
      return <ReasoningItem reasoning={item} />;
    default:
      return null;
  }
}

Benefits

No chunk accumulation - Each item emission is complete
Natural React updates - Setting state triggers re-render automatically
Concurrent item handling - Function calls and messages stream in parallel
Works with React 18+ - Compatible with concurrent features and Suspense
Type-safe - Full TypeScript inference for all item types

Comparison with Chunk Accumulation

Traditional streaming requires manual accumulation:

// Traditional approach - manual accumulation
const [text, setText] = useState('');

for await (const chunk of result.getTextStream()) {
  setText((prev) => prev + chunk); // Must accumulate manually
}

With items, each emission replaces the previous:

// Items approach - replace by ID
for await (const item of result.getItemsStream()) {
  setItems((prev) => new Map(prev).set(item.id, item)); // Complete replacement
}

The items approach is especially powerful when the model produces multiple outputs simultaneously (e.g., thinking + tool calls + text).

Migrating from getNewMessagesStream()

getNewMessagesStream() is deprecated in favor of getItemsStream(). The migration is straightforward:

// Before (deprecated)
for await (const message of result.getNewMessagesStream()) {
  if (message.type === 'message') {
    console.log(message.content);
  }
}

// After
for await (const item of result.getItemsStream()) {
  if (item.type === 'message') {
    console.log(item.content);
  }
}

The key difference: getItemsStream() includes all item types (reasoning, function calls, etc.), not just messages.

Next Steps

Streaming - All streaming methods including getItemsStream()
Tools - Creating typed tools with Zod schemas

​The Items Paradigm

​Messages vs Items

​Item Types

​How Streaming Works

​React Integration

​Benefits

​Comparison with Chunk Accumulation

​Migrating from getNewMessagesStream()

​Next Steps