Budget

Cap what a single run may spend in money, tokens, or working time.

Overview

A budget sets ceilings on a run. When a ceiling is crossed the run stops with a message naming the exact limit that tripped, and the TUI tracks consumption live while the run is still going.

Every limit is optional and an unset limit is unlimited, so you can cap money, tokens, time, or any combination. Declare no budget at all and runs are unbudgeted, which is the default.

There are two ways to declare one, and they compose:

A run-wide budget

agents:
  root:
    model: openai/gpt-4o-mini
    description: An agent on a short leash.
    instruction: You are a helpful assistant.

budget:
  max_cost: 0.50
  max_tokens: 100000
  max_time: 10m

Named budgets

Define budgets by name under the top-level budgets key, then have each agent opt in by listing names in its own budgets field. The fields are the same three.

budgets:
  shell-work:
    max_cost: 0.03
    max_tokens: 8000
  research:
    max_time: 1m

agents:
  root:
    model: openai/gpt-4o-mini
    description: Does shell work.
    instruction: You are a helpful assistant.
    budgets: [shell-work]
  researcher:
    model: openai/gpt-4o-mini
    description: Answers questions.
    instruction: You answer questions concisely.
    budgets: [shell-work, research]

An agent may list several budgets; all of them apply, and the first to be exhausted stops the run. A run-wide budget applies on top of any named budget, so the ceiling that binds is whichever runs out first.

Referencing a budget name that isn't defined is a config error, caught at parse time rather than silently leaving the agent uncapped.

A name is one shared pot

When several agents reference the same budget name they draw from the same ceiling — not a copy each. Above, root and researcher share shell-work: together they cannot spend more than $0.03.

This is deliberate, and it is the whole reason budgets are worth having. If each agent received its own allowance, a run could spend max_cost × N simply by fanning out to N sub-agents, and the ceiling would mean nothing for exactly the workloads that most need one.

Give agents distinct budget names when you want independent pots.

The same applies to the run-wide budget: every sub-session inside a run (transferred tasks, sub-agents, skills) spends from that one wallet.

Scope: a budget spans the session

Spend accumulates for the life of the session, across every message you send — it does not reset each time you hit enter. A max_cost: 0.50 you could re-spend on every message would not be a ceiling at all.

Starting a new session starts a fresh budget. It is a per-session ceiling, not a lifetime quota across sessions.

What stops a run

Crossing any limit — run-wide or named — stops the run and produces:

• an assistant message in the transcript naming the limit and the amounts,
• a budget_exceeded event carrying budget, limit, used, max, config_path and, under stop_message, the assistant stop message itself (agent name, role, content and timestamp only),
• a notification hook at warning level,
• a stream end reason of budget_exceeded, so a stopped run is distinguishable from a completed one in telemetry.

The message names the exact YAML path to raise, so there is no ambiguity about which of several budgets tripped:

Execution stopped after reaching the configured budgets.shell-work.max_cost
limit (used $0.0312 of $0.0300).

Unlike max_iterations, a budget stop is terminal — there is no prompt offering to continue. A budget is a ceiling you set deliberately, so raising it means editing the config rather than answering a dialog.

Budget stops in evaluation output

When a budgeted agent is exercised with docker agent eval, a budget stop is recorded as a structured termination. It is not an error, and it is distinct from an ordinary stream stop: the run output JSON exposes it as an optional eval_result.termination object on the affected session.

"eval_result": {
  "passed": true,
  "termination": {
    "reason": "budget_exceeded",
    "budget": "run",
    "limit": "max_cost",
    "used": "$0.0312",
    "max": "$0.0300",
    "config_path": "budget.max_cost",
    "message": "Execution stopped after reaching the configured budget.max_cost limit (used $0.0312 of $0.0300)."
  }
}

• reason is always budget_exceeded. The other fields are optional and are copied from the runtime's budget_exceeded event through an allow-list: only budget, limit, used, max, config_path, and message are ever taken, each sanitized (invalid UTF-8 and control characters stripped, bounded length) and omitted when missing or unusable.
• The stored session (SQLite database and sessions JSON) keeps the stop marker at its chronological position, followed exactly once by the assistant stop message rebuilt from the event's embedded stop_message (again only agent name, role, content, and timestamp are taken, sanitized the same way). When the event carries no usable stop_message, the marker stands alone; nothing is invented from termination.message.
• The termination is informational: it does not change passed, failures, or error. A run that completed normally or failed with an error simply has no termination field, and older outputs written before the field existed load unchanged.

Tracking spend in the TUI

The sidebar's Token Usage panel lists every active budget by name, with consumption against each ceiling it declares:

run        $0.12/$0.50 · 12.3K/100.0K · 2m14s/10m
shell-work $0.09/$0.10 · 4.3K/20.0K

Only the ceilings you configured appear. Each reading is colored by the sidebar's shared gauge bands — the same ones a context gauge uses as it nears compaction — so a budget turns amber well before its ceiling and red just short of it, and a run about to be stopped is visible before it stops.

For a per-agent view of who spent what, set Sidebar info mode to Detailed in /settings → Appearance: the Agents section then reports each agent's cost alongside its effort and context. The budget line deliberately does not repeat that breakdown — the same numbers twice would crowd the sidebar's narrowest column. The per-agent split is still carried on the budget_usage event for programmatic consumers, and /cost has a By Agent section.

Limits and caveats

Unpriced models do not count towards max_cost

Only responses the runtime can price count towards max_cost. A model with no pricing data — an unknown model ID, or a custom endpoint such as a local or private deployment — contributes nothing, because there is no honest number to add.

Such a run emits a warning and the TUI marks the reading (unpriced spend), rather than silently reading low because the spend is invisible. To make a custom endpoint count, price it explicitly with a model-level cost block:

models:
  local:
    provider: openai
    model: my-model
    base_url: http://localhost:8000/v1
    cost:
      input: 0.15
      output: 0.60

agents:
  root:
    model: local
    description: A locally-served agent with real cost accounting.
    instruction: You are a helpful assistant.

budget:
  max_cost: 0.50

Limits are checked at turn boundaries

A run is checked between turns, so it can overshoot by at most the turn already in flight. max_time in particular will not interrupt a model call or tool that has already started; the run stops at the first boundary after the limit is reached.

This is the same granularity max_iterations has, and it keeps the ceiling out of the streaming hot path. Set limits with a little headroom rather than at the exact number you cannot exceed.

max_tokens here is not the model's max_tokens

The max_tokens in a budget is a cumulative count of input+output tokens across the whole run. It is unrelated to the provider- or model-level max_tokens, which caps the output of a single response.

It is also not the session's context length: compaction resets that, while the budget keeps counting.

Examples

Cap money only, and let the run take as long as it needs:

agents:
  root:
    model: openai/gpt-4o
    description: A cost-capped agent.
    instruction: You are a helpful assistant.

budget:
  max_cost: 5.00

Cap working time for an unattended job:

agents:
  root:
    model: openai/gpt-4o-mini
    description: A time-boxed agent.
    instruction: You are a helpful assistant.
    toolsets:
      - type: shell

budget:
  max_time: 15m

See examples/budget.yaml for a runnable configuration.