Cross-Chain APIGuides

Streaming Quotes

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The Cross-Chain API supports streaming of swap quotes using Server-Sent Events (SSE). Quotes are delivered progressively as they’re discovered, so users can act on them immediately.

Why Streaming?

  • ⚡ Faster first quote — get actionable quotes faster
  • 🔄 Progressive discovery — quotes stream in as they’re found, no blocking waits
  • 🛠️ Immediately executable — every quote includes full transaction details
  • 🎯 Better UX — show users the first good option instead of making them wait

Endpoint

GET /cross-chain/quotes/stream

Streams cross-chain swap quotes as SSE events. Each quote is delivered as a standalone event with everything needed for execution.

Same params as /cross-chain/quotes, except:

  • No sortQuotesBy — quotes stream in discovery order always
  • The maxNumQuotes defaults to 5 for the streaming endpoint (vs. 3 for the non-streaming /quotes endpoint). The stream closes after delivering this many quotes or reaching the timeout, whichever comes first.

After calling the endpoint with proper parameters, you will get back Server-Sent Events with the following message types:

Quote Found

data: {
    "event": {
      "type": "quote",
      "data": {
        "quote": { /* full quote object */ },
        "allowanceTarget": "0x000..."
      }
    },
    "zid": "0xbed7b45844099af94219ba8c"
}

Stream Done

data: {
    "event": {
      "type": "result",
      "data": {
         "liquidityAvailable": true
      }
    },
    "zid": "0xbed7b45844099af94219ba8c"
}

Error (if stream fails)

data: {
    "event": {
      "type": "error",
      "data": {
        "message": "Stream failed due to server error",
        "code": "STREAM_ERROR"
      }
    }
}

Timeout

The stream has a 30-second server-side timeout. If no quotes are found within this window, a result event with liquidityAvailable: false is sent and the stream closes.

This timeout is not configurable. If you’re getting timeouts:

  • Remove excludedBridges or broaden includedBridges
  • Increase slippageBps
  • Try a more liquid token pair

Reconnection

SSE connections may be dropped by network intermediaries (proxies, load balancers). If the connection closes without a result or error event:

  • The stream is not resumable, just open a new connection with the same parameters
  • Each new connection generates a new zid
  • Add a 1–2 second delay between reconnection attempts

Client Example

const quoteParams = new URLSearchParams({
    originChain: '8453', // Base mainnet
    destinationChain: '42161', // Arbitrum mainnet
    sellToken: '0x4200000000000000000000000000000000000006', // WETH on Base
    buyToken: '0xaf88d065e77c8cc2239327c5edb3a432268e5831', // USDC on Arbitrum
    sellAmount: '1000000000000000000', // Amount of sellToken in base units
    originAddress: '$USER_TAKER_ADDRESS', // Address that will make the trade
});
const headers = {
    '0x-api-key': '[api-key]', // Get your live API key from the 0x Dashboard (https://dashboard.0x.org/apps)
};
const resp = await fetch('https://api.0x.org/cross-chain/quotes/stream?' + quoteParams.toString(), { headers });
const reader = resp.body.getReader();
const decoder = new TextDecoder();
while (true) {
  const { value, done } = await reader.read();
  if (done) break;
  const chunk = decoder.decode(value, { stream: true });
  chunk.split("\n").forEach(line => {
    if (line.startsWith("data:")) {
      const parsed = JSON.parse(line.slice(5).trim());
      console.log("SSE event:", parsed);
    }
  });
}

You can find a full streaming example with NextJS in 0x-examples.