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Preflight Stack / Temporary File Relay
x402 service · 0.005–0.02 USDC per relay

Temporary file handoff for agents and remote systems.

When one agent has an artifact another needs but they do not share storage, Temporary File Relay creates a paid capability URL for a passive file. The link works for seven days and supports files up to 250 MiB.

Open API docs →View Agentic Market listing
POST /v1/file-slot
{
  "filename": "research-report.pdf",
  "content_type": "application/pdf",
  "size_bytes": 12582912
}
Pricing and limits

Pay once for a bounded, seven-day handoff.

Pricing is based on the exact declared file size. Payments use native USDC on Base through x402.

1 byte–25 MiB

0.005 USDC for reports, images, structured outputs, and compact archives.

>25–250 MiB

0.02 USDC for larger datasets, media, and bundled artifacts.

Seven-day link

Published capability URLs expire automatically after exactly seven days.

How a handoff works

Payment, upload, verification, then publication.

The stages stay separate so a settled payment is never mistaken for a completed upload.

01

Declare

Send the filename, approved content type, and exact byte size.

02

Pay

The API returns HTTP 402 when payment is required; Coinbase x402 infrastructure verifies and settles native USDC on Base.

03

Upload

The Relay issues an opaque slot and a short-lived signed upload URL for a private Cloudflare R2 object.

04

Complete

Call the completion route. The service verifies exact size and content type before publishing the capability URL.

Good fits

Passive artifacts that need to cross systems.

  • Agent-to-agent file transfer
  • Generated reports, images, archives, and data exports
  • Cross-tool handoff without shared cloud credentials
  • Temporary workflow outputs needed for seven days or less
Not a good fit

Keep sensitive and durable data elsewhere.

  • Passwords, private keys, secrets, or personal records
  • Regulated or otherwise sensitive data
  • Active executable web content
  • Permanent storage or backup
  • Files over 250 MiB
Capability URL boundary: anyone who possesses a completed file URL can download the artifact until it expires. Opaque, unguessable URLs reduce accidental discovery; they do not make this private file sharing. Each artifact also has a 2,000-read lifetime ceiling plus client and artifact rate limits.
Why completion is separate

Publish only what actually reached storage.

Payment creates the right to upload; it does not prove an upload succeeded. Completion verifies the stored object's exact declared size and content type before returning a public capability URL.