Streaming Quotes

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

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

Stream Done

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

Error (if stream fails)

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

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

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

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