The agent economy is growing a set of its own payment standards. x402, ACP, AP2/UCP and MPP are the names most often cited, each addressing a different part of the picture — from machine-to-machine payments to checkout, mandates and card-based flows. For developers, the practical question is not which one wins, but where each one sits and what remains unsolved beneath them. This is a map, not a scorecard.

Different layers, different jobs

These protocols are not all trying to do the same thing. Read broadly, they cover:

  • machine payments, where software pays software directly;
  • checkout, where an agent completes a purchase;
  • mandates, where the authority to pay is expressed;
  • card-based flows, where agent tokens ride on existing card rails.

Each defines part of the interaction. None of them, on its own, settles value between institutions.

Where they meet the real world

Whatever the protocol, an operation eventually has to clear. Today that means correspondent banking, local instant schemes, card networks, stablecoin networks or a hub of participating institutions. The protocol shapes the instruction; the settlement layer decides how and where the money actually moves. That is why a settlement layer sits beneath the protocols rather than competing with them.

What a settlement layer adds

Beneath the standards, the useful functions are consistent:

  • netting of offsetting flows, so only the remainder leaves;
  • instant internal settlement between participants;
  • internal FX;
  • routing by cost, settlement time, reliability and regulatory fit.

Protocols define how agents ask. A settlement layer decides how the answer is delivered. That division of labour is deliberate: standardisation at the edges, efficiency in the middle. An agent developer can adopt whichever protocol suits the use case and still reach the same settlement machinery beneath, without building a connection to every rail and institution by hand.

In short

  • The agent protocols address different layers, not one race.
  • Checkout, mandates, card flows and machine payments each sit elsewhere.
  • All of them still need settlement beneath them.
  • Netting, internal FX and routing are the settlement functions that matter.

See how protocols connect to rails in the developer documentation.