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Fixed Allowances (AI Budgets)

BLUF: A fixed delegation is a hard, cumulative spending budget: "this counterparty may pull up to X total, ever, optionally until time T." It never refills. That makes it the natural primitive for giving an AI agent a wallet it cannot drain — the failure mode is bounded by construction, not by prompt discipline.

The pattern: agent gets a budget, not a key

The worst way to fund an autonomous agent is to hand it a private key to a funded wallet — every bug, prompt injection, or hallucinated "payment" has the full balance as its blast radius. The fixed-delegation pattern inverts this:

  1. The operator (human or treasury) keeps custody of the funds.
  2. The operator creates a fixed delegation toward the agent's spending counterparty: cumulative cap, optional expiry.
  3. The agent's payments are executed as pulls against the delegation. The program — not the agent's judgment — enforces the ceiling.
  4. When the budget is spent or the expiry passes, spending stops. Period. No prompt can negotiate with an on-chain cap.

This is the same shape as a card-style pre-authorization: a bounded envelope, opened once, drawn down until empty.

Standards context: MPP

Agentic-payment flows are being standardized in the MPP spec (github.com/tempoxyz/mpp-specs — PR #270), which covers this kind of agent-budget delegation. If you're building agent payments, track that spec alongside this program — the fixed delegation is a natural settlement primitive underneath it.

Semantics, precisely

Property Behavior
Cap Cumulative — the total ever pullable. Each pull subtracts; nothing refills.
Expiry Optional. After it passes, remaining budget is unspendable.
No periods Unlike recurring delegations, there's no rollover and no per-period counter — just a depleting total.
Revocation revokeDelegation, signed by the delegator, effective immediately — remaining budget dies with it.
Top-up There is no in-place increase; issue a new delegation when the budget runs dry. Treat that as a feature — refilling is a deliberate human act, an approval checkpoint.

Setup mirrors the recurring flow (ADR-001 direct-delegation set): initSubscriptionAuthority once per delegator, then createFixedDelegation; pulls go through transferFixed; the kill switch is revokeDelegation.

Worked example: research agent with a $50 budget

An operator wants an agent to buy API credits and datasets, up to $50 total, this month only:

  • Cap: 50_000_000 base units (for a 6-decimal stable mint — base units, always).
  • Expiry: end of month.
  • Agent purchases $12, $3, $20 → ✓ ✓ ✓ (35 spent). Attempts $20 more → ✗ rejected — would exceed the cumulative $50. The agent can still spend $15, nothing more.
  • Month ends → any remainder is dead. Operator reviews the spend log (every pull emitted an event) and decides, consciously, whether next month's delegation should exist and at what size.

Why this beats the alternatives

  • vs. funding the agent's own wallet: a compromised or confused agent can lose at most the remaining cap — and the operator can revokeDelegation the moment something looks wrong, instantly stranding the budget.
  • vs. a recurring delegation: recurring refills every period whether or not you reviewed anything. Fixed makes every refill a human decision. For autonomous spenders, defaulting to fixed is the conservative choice; graduate to recurring only when the spend pattern is boring and audited.
  • vs. token-level approve(amount): a plain SPL approval is a single delegate slot with no expiry semantics, no event trail designed for billing reconciliation, and it collides with any other delegation use of that account. The program multiplexes many delegations through one authority and enforces expiry and revocation uniformly.

What the cap does not protect

The cap bounds how much leaves the wallet — not whether each purchase was wise. An agent can still spend its whole budget on garbage. Pair the on-chain ceiling with off-chain review of the event stream, and keep budgets small enough that "all of it, wasted" is an acceptable worst case.

Recap: fixed delegation = depleting cumulative cap + optional expiry + instant revocation. Give agents budgets, not keys; make refills deliberate; let the program — not the model — hold the line.

Sources for every claim on this page: About → Sources.