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Metering

Off-chain usage tracking by the server.

Metering is how the server tracks what the client has consumed. All metering happens off-chain — no transactions during consumption. The accumulated usage is then settled periodically in a single on-chain transaction.

Metering modes

ModeUnitDescription
per-callFixed per invocationEach API call costs a fixed amount
per-secondPer second of connectionFor streaming or long-lived connections
per-bytePer byte transferredFor data-heavy endpoints
per-computePer compute unitFor variable-cost operations (inference, rendering)
customServer-definedServer publishes a custom metering function

How it works

  1. Client sends a request with AMP-Channel, AMP-Seq, AMP-Sig headers.
  2. Server validates credentials (channel exists, signature valid, seq monotonic).
  3. Server serves the request.
  4. Server increments the local metering counter.
  5. No on-chain transaction occurs.

The server maintains a ChannelUsage record per channel:

interface ChannelUsage {
  callCount: number
  bytesConsumed: number
  secondsConsumed: number
  totalAmount: number      // rate * usage
  seqStart: number
  seqEnd: number
  periodStart: number      // unix timestamp
}

Metering proofs

When the server settles, it produces a MeteringProof:

{
  "channel": "<channel_pda_base58>",
  "amount": 4500000,
  "callCount": 4500,
  "periodStart": 1711234567,
  "periodEnd": 1711238167,
  "seqStart": 1001,
  "seqEnd": 5500,
  "serverSignature": "<ed25519_signature>"
}

The signature covers: SHA256(channel || amount || callCount || periodStart || periodEnd || seqStart || seqEnd).

Pricing configuration

Servers declare pricing in their manifest:

{
  "pricing": {
    "default": {
      "mode": "per-call",
      "rate": "1000",
      "token": "EPjFWdd5AufqSSqeM2qN1xzybapC8G4wEGGkZwyTDt1v",
      "minDeposit": "1000000",
      "settleInterval": 3600
    },
    "routes": {
      "/v1/inference": { "mode": "per-call", "rate": "10000" },
      "/v1/stream": { "mode": "per-second", "rate": "1000" }
    }
  }
}

All monetary values are in the token's smallest unit. USDC has 6 decimals: "1000" = $0.001.

Next steps