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A “rail” is the standard a paid service uses to ask for and accept payment. SAULT supports the common HTTP 402 rails, and more over time. Your agent never has to know which one a service uses — it calls the URL, SAULT handles the rest.

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What SAULT supports today

RailChains
x402Base, Solana
MPPTempo, Solana
Both work the same way from your side: the service asks for payment, SAULT pays from the vault within the agent’s limits, and your agent gets the result with a receipt.

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When a service supports more than one

SAULT prefers the chain where your vault has the most available balance. You can pin a preference per agent if you need predictable routing.

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New rails later

The agent’s contract — call a URL, get a result — doesn’t change when SAULT adds a rail. Existing agents pick up new rails automatically.