Sponsored gas

A delegated agent can settle without holding SUI for gas. The gateway can sponsor gas after the agent signs a Sui personal message that proves it holds the registered delegated key. Sponsorship authenticates gas only, not settlement. Settlement still requires a valid on-chain pay and a verified payment proof.

When you need it

The SDK payer prefers agent gas when configured, otherwise sponsored gas when a sponsor client is configured.

Personal-message challenge

BYO delegated keys must not use unbound sponsor paths. The protocol is a personal-message challenge (signPersonalMessage / IntentScope PersonalMessage) before the gateway attaches gas:

1. Challenge. Agent requests a single-use nonce bound to the registered delegate address and the target grant/pool (POST /api/sponsor/personal-message/challenge).
2. Signed payload. The agent signs a domain-separated personal message with the delegated key. Domain separator: suipay:sponsor-personal-message:v1 (not a settlement digest).
3. Bindings. The payload covers nonce, expiry, delegate, pool id, grant id, network, package id, request id (for example the payment/challenge id), and a SHA-256 of the pre-sponsor transaction kind (not the post-sponsor executable digest the sponsor builds later).
4. Sponsor. Agent calls POST /api/sponsor with the kind bytes plus the personal-message fields. The gateway verifies signature, address derivation, unconsumed nonce, grant registration, and that the kind is a permitted spend_account::settle_policy_payment (or refundable spend) for that grant.
5. Execute. Agent signs the sponsored transaction digest; gateway or client submits. Nonce is consumed so the same challenge cannot authorize another kind.

What the challenge does not do

• It does not authorize delivery of a paid resource by itself.
• It does not bypass grant policy, budgets, or pay checks.
• A valid personal message without a valid on-chain payment does not settle.

Quotas and safety

Sponsorship is rate- and quota-limited per signer, separately from token budget. Failed, aborted, and ambiguous transactions may still count against gas quota. Treat sponsorship as part of the blast radius of a leaked delegated key: an attacker can burn gas up to the remaining quota as well as spend within grant caps.

MCP OAuth

OAuth-session delegates use the platform's existing sponsor path for that connection. BYO keys always use the personal-message challenge above when requesting sponsored gas.