agent-control-evaluator-budget 8.1.2

Budget evaluator for agent-control -- cumulative LLM cost and token tracking

agent-control-evaluator-budget

Budget evaluator for agent-control that tracks cumulative LLM token and cost usage per scope and time window.

Install

pip install "agent-control-evaluators[budget]"

Fallback direct wheel install:

pip install agent-control-evaluator-budget

For local development:

uv pip install -e evaluators/contrib/budget

Quickstart

from agent_control_evaluator_budget.budget import (
    BudgetEvaluatorConfig,
    BudgetLimitRule,
    ModelPricing,
)

config = BudgetEvaluatorConfig(
    budget_id="support-daily",
    limits=[
        BudgetLimitRule(
            scope={"agent": "support"},
            group_by="user_id",
            window_seconds=86_400,
            limit=500,
            limit_unit="usd_cents",
        ),
        BudgetLimitRule(
            scope={"agent": "support"},
            group_by="user_id",
            window_seconds=86_400,
            limit=50_000,
            limit_unit="tokens",
        ),
    ],
    pricing={
        "gpt-4.1-mini": ModelPricing(input_per_1k=0.04, output_per_1k=0.16),
    },
    model_path="model",
    metadata_paths={
        "agent": "metadata.agent",
        "user_id": "metadata.user_id",
    },
    unknown_model_behavior="block",
)

The evaluator reads token usage from standard fields such as usage.input_tokens and usage.output_tokens. Configure token_path only when your event shape uses a custom location.

Scope and group_by

Each BudgetLimitRule has a static scope and an optional group_by field.

scope filters which events a rule applies to. A rule with scope={"agent": "support"} only applies when extracted metadata contains agent="support". An empty scope is global.

group_by creates independent buckets per extracted metadata value. The common per-user pattern is:

BudgetLimitRule(
    scope={"agent": "support"},
    group_by="user_id",
    window_seconds=86_400,
    limit=500,
    limit_unit="usd_cents",
)

With metadata_paths={"user_id": "metadata.user_id"}, each user gets a separate daily budget inside the support scope.

Budget pools

budget_id identifies the accumulated budget pool.

Evaluators with the same budget_id share accumulated spend and token totals across all evaluator instances. Each evaluator still evaluates using its own configured rules -- the shared state is the bucket (the rolling sum), not the rule set. Evaluators with different budget_id values are fully isolated.

Use stable names such as support-daily, billing-global, or tenant-acme-monthly. Avoid generating a new budget_id per request unless each request should have an isolated budget.

Pricing

ModelPricing stores cost rates in cents per 1K tokens:

ModelPricing(input_per_1k=0.04, output_per_1k=0.16)

input_per_1k is applied to input tokens. output_per_1k is applied to output tokens.

Pricing and model_path are required when any rule uses limit_unit="usd_cents". Token-only rules can omit both. If an event uses a model that is not in the pricing table and a cost rule exists, unknown_model_behavior="block" fails closed. Use "warn" to log a warning and treat the cost as 0.

Dual Ceiling Pattern

Use two evaluators when cost and token ceilings need independent control records or different budget_id pools:

cost_config = BudgetEvaluatorConfig(
    budget_id="support-cost-daily",
    limits=[
        BudgetLimitRule(
            scope={"agent": "support"},
            group_by="user_id",
            window_seconds=86_400,
            limit=500,
            limit_unit="usd_cents",
        )
    ],
    pricing={
        "gpt-4.1-mini": ModelPricing(input_per_1k=0.04, output_per_1k=0.16),
    },
    model_path="model",
    metadata_paths={"agent": "metadata.agent", "user_id": "metadata.user_id"},
)

token_config = BudgetEvaluatorConfig(
    budget_id="support-token-daily",
    limits=[
        BudgetLimitRule(
            scope={"agent": "support"},
            group_by="user_id",
            window_seconds=86_400,
            limit=50_000,
            limit_unit="tokens",
        )
    ],
    metadata_paths={"agent": "metadata.agent", "user_id": "metadata.user_id"},
)

This pattern lets cost and token budgets reset, alert, and roll out independently. A single evaluator can also contain both rules when one shared pool and one control result are sufficient.

Limitations

InMemoryBudgetStore is single-process only. State is lost on restart and is not shared across workers or pods.

Use a distributed store for production deployments that run multiple processes, multiple workers, or multiple pods.