Cost and Budget

Delta agents operate within explicit budget ceilings. Every task declares a budget at send() time, and the engine enforces it structurally: agents cannot exceed what the task allows.

Cost model

Cost is a multi-axis vector that tracks resource consumption across several dimensions:

type Cost = {
  tokens: number;
  durationMs: number;
  memory?: number;
  latency?: number;
  money?: Money;
  content?: ContentCost;
};

type Money = {
  value: number;
  currency: string; // ISO 4217, e.g. "USD", "EUR", "NGN"
};

type ContentCost = {
  count: number;
  bytes: number;
  unitType?: "tokens" | "pages" | "images" | "bytes";
  itemSize?: number;
};

• tokens: model API token consumption. Always tracked, always enforced.
• durationMs: wall-clock execution time. Always tracked, always enforced.
• memory: memory retrieved or stored during execution. Optional axis.
• latency: time spent waiting on external operations. Optional axis.
• money: financial cost as an explicit value and currency pair. Optional axis. A bare number would assume a single currency; the explicit pair means governance math never silently mixes regions.
• content: attachment or content resource consumption. Populated but not yet enforced by any budget axis.

Budget enforcement is per-axis. An axis that is not declared in the budget is unlimited on that axis.

Setting a budget

Budgets are set per task at delta.send():

const result = await delta.send({
  goal: "Process order ORD-42",
  agentName: "support-agent",
  budget: {
    tokens: 5000,
    durationMs: 60_000,
  },
});

The default budget is { tokens: 10_000, durationMs: 300_000 } when none is specified.

Budget enforcement

The engine checks budget before every action execution. If the remaining budget is insufficient to cover the action's estimated or observed cost, the action is blocked. The task transitions to failed status with budget exhaustion as the reason.

Budget enforcement operates at every governance gateway check, alongside schema validation, prerequisite checking, risk assessment, and approval gates. The sequence is deterministic: budget is checked before any action executes, not after.

Anticipated cost

Actions and workflows may declare an estimatedCost: the developer's expectation of what the operation should consume.

const lookupCustomer = delta.action({
  name: "lookup-customer",
  estimatedCost: { tokens: 500, durationMs: 2000 },
  // ...
});

Anticipated cost seeds the engine's cost estimator with a prior, so the engine starts from a calibrated expectation instead of a cold one. The engine continuously refines its estimate from observed behavior and may adjust when actual consumption diverges from the estimate.

Cost in delegation

When a parent delegates work to a subtask, it reserves a portion of its own budget for the child. The subtask receives a scoped budget and cannot exceed it. Any remaining budget at the child's completion is refunded to the parent. This prevents a runaway subtask from consuming the entire parent budget.

Budget in tool execution

Tools may declare an optional budget for cost tracking. Unlike action budgets, tool budgets are purely advisory for cost awareness. When a tool's budget is exceeded, the engine blocks further calls and returns a humanized message.

Observing costs

The task state snapshot carries the full spent cost at any point. Call delta.inspect(taskId) to read the current budget state, including what has been spent and what remains.