What is x402?

x402 is a payment protocol that enables payments over HTTP; it was introduced in May 2025, with an updated version 2 of the spec released in December 2025.

When a client makes an HTTP request, the server may respond with HTTP 402 (Payment Required), and a PAYMENT-REQUIRED header. The header encodes a payload like this:

{
  "x402Version": 2,
  "error": "Purchase 12 credits for $0.04",
  "resource": {
    "url": "https://askjune.ai/app/chat",
    "description": "Purchase usage credits on June AI",
    "mimeType": "application/json"
  },
  "accepts": [
    {
      "scheme": "exact",
      "network": "eip155:8453",
      "amount": "40000",
      "asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
      "payTo": "0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045",
      "maxTimeoutSeconds": 60,
      "extra": {
        "name": "USD Coin",
        "version": "2"
      }
    }
  ]
}

This lets the server tell the client what the request costs and which payment methods it accepts. In the example above, the server will only accept a payment of 0.04 USDC on Base.

The client can then retry the request, but with a PAYMENT-SIGNATURE header attached, which encodes a payment payload that matches the server's requirements, and must be signed.

The server verifies that the payment payload matches its requirements, then uses an x402 facilitator to validate and settle the transaction. If the payment succeeds, the server fulfills the client's request.

While the protocol is complex under the hood, we have implemented it to feel completely invisible to the user.

How June uses x402

When you run out of credits on June, you have a few options:

1. Upgrade to a higher tier: Our Pro and Max plans have higher credit limits that refresh every day, and they provide the best value for using our platform.
2. Pay for this request: Make a small one-off payment to buy enough credits to complete this request; this is great for when you need "just one more prompt" to finish the task you were working on.
3. Buy a credit pack: If you need more credits but you don't want to upgrade your plan (or you're already on the highest tier), you can buy a bundle of credits in one purchase. Unlike the credits that are free as part of your June plan, and refresh every 5 hours, these credits never expire. We also offer discounted pricing on larger bundles, so the more credits you buy, the better the value.

If you choose (2) or (3) to buy more credits, you can pay with x402. Either tap the "Pay $x for this request" button, or navigate to the credit top-up page.

Once you've made your selection, your browser wallet will pop up, asking you to sign a transaction.

After you sign, the browser will encode the signed transaction into the x402 PAYMENT-SIGNATURE header as described above, and send the request to June. Your credits will be topped up, and you'll be able to continue using the platform.

We're launching with support for USDC on Base, but will expand support to other blockchains soon.

Why x402?

x402 keeps the entire payment flow simple, both for our developers, and for the user.

For users, it's a fast, in-context checkout: pay with the wallet you already use, without leaving the page, with a single click to sign.

For our team, we can add our x402 payment handling to any API endpoint, allowing us to charge per request where we know exactly how much that request will cost. All of the crypto-specific verification/validation, transaction broadcasting, and waiting for requests to finalise, we can delegate to the x402 facilitator, which allows us to stay focused on improving June.

These new options will allow our users to get more out of June, and we think this payment experience is better than ever. We're excited for you to try it out, and let us know what you think!

Finally, this lays the groundwork for a simple, crypto-native, payments API; easy for humans to use today, and a great fit for AI agents when we open up our APIs in the near future.