Smart contract wallets for payment agents

Smart contract wallets — account abstraction on Ethereum and similar patterns on other chains — provide a technical foundation for agent-initiated payments that plain externally-owned accounts don't. The pattern is worth understanding independent of the specific chain.

Written December 2025 from an implementation review.

What account abstraction adds

• Session keys. A key with limited authority (specific merchants, capped amounts, expiry) issued to an agent. The main account key doesn't move.
• Custom authorisation logic. The wallet contract can enforce arbitrary conditions on transactions — velocity limits, merchant allowlists, step-up requirements.
• Batching. Multiple actions can be authorised together as a single transaction.
• Gas abstraction. The wallet can pay gas in the token being spent, or gas can be sponsored by a third party.

What the mandate model looks like

A smart contract wallet supporting agent payments would encode a mandate as an authorisation:

• Authorise session key K
• To spend up to $X per transaction
• Cumulative up to $Y per period
• At merchants matching pattern P
• Until expiry E
• With step-up required above threshold T

The authorisation is on-chain, verifiable, and revocable at any time.

What still needs work

• Cross-chain mandate portability. A mandate on one chain doesn't automatically apply on another. Some proposals address this; none are widely adopted.
• Human review of authorisation. The user issuing the mandate needs to understand what they're signing. Current UX for this is poor.
• Off-chain integration. The mandate is on-chain; the agent's decisions are off-chain. Reconciling the two audit trails is nontrivial.

Smart contract wallets are the strongest technical foundation for agent payments that currently exists. The integration questions are substantial, but the primitives are in place.