Cost & budget

LogicGrid calculates a USD cost estimate for every LLM call and accumulates it across an entire run. You can read the total off the trace, alert on a threshold via BudgetWarningEvent, or hard-stop the run with MaxBudgetUsd.

How cost is computed

Each LlmClient knows the rate card for its provider (see PricingTable). After every LLM response, the framework multiplies prompt-token and completion-token counts by the per-token rates and emits a CostEstimate:

public sealed class CostEstimate
{
    public decimal InputCostUsd  { get; }
    public decimal OutputCostUsd { get; }
    public decimal TotalCostUsd => InputCostUsd + OutputCostUsd;
    public string  Currency => "USD";
    public static CostEstimate Zero { get; }
    public static CostEstimate operator +(CostEstimate a, CostEstimate b);
}

Ollama and other unpriced/local providers return CostEstimate.Zero — the field is always present, you just see $0.0000.

Reading total cost from the trace

var ctx = new AgentContext().WithTracing(out var trace);
await admin.RunAsync(input);

Console.WriteLine($"Cost: ${trace.TotalCost.TotalCostUsd:0.0000}");
Console.WriteLine($"  in:  ${trace.TotalCost.InputCostUsd:0.0000}");
Console.WriteLine($"  out: ${trace.TotalCost.OutputCostUsd:0.0000}");

Capping spend with `MaxBudgetUsd`

Set the cap on the admin's AdminOptions. The admin checks spend after every agent completes and stops the run with BudgetExceededException once it crosses the limit.

var admin = new GroupChatAdmin<string, string>(
    "Editorial", llm, agents,
    options: new AdminOptions
    {
        MaxBudgetUsd = 0.50m,                  // hard cap
        BudgetWarningThreshold = 0.75f,        // warn at 75 %
    });

try
{
    var output = await admin.RunAsync("…");
}
catch (BudgetExceededException ex)
{
    Console.WriteLine($"Run stopped: {ex.Message}");
}

ReflexionAdmin carries the same fields on its ReflexionOptions.

Budget events

BudgetWarningEvent and BudgetExceededEvent fire on the bus before the exception is thrown. Subscribe to them for alerting:

ctx.EventBus!.Subscribe<BudgetWarningEvent>(e =>
    myAlerts.Notify($"run {e.RunId} at {e.PercentUsed:P0} of budget"));

ctx.EventBus!.Subscribe<BudgetExceededEvent>(e =>
    myAlerts.Page($"run {e.RunId} exceeded ${e.LimitUsd:F2}"));

Both events are also captured on the trace under trace.BudgetEvents.

When the cost is `$0.0000`

Three reasons:

You're running Ollama / a local provider. No rate card, no cost. This is by design.
The provider is OpenAiCompatibleClient pointing at vLLM / TEI / your own host. Rate is unknown to LogicGrid.
Token usage was zero because the call failed before the LLM responded.

If you want to track real cost for a self-hosted provider that bills internally, supply your own pricing — wrap the client and override the cost calculation, or compute it externally from the TokenUsage on each LlmCallCompletedEvent.

Common pitfalls

Budget cap on a chatty group chat with no DONE clause. The loop runs to MaxLoops every time, hitting the budget before finishing. Make termination explicit in the agents' system prompts.
Underestimating MaxBudgetUsd. A reflexion loop with a slow critic can use 5x the tokens of a single-shot pipeline. Run a few representative requests with tracing on, look at trace.TotalCost, then set the cap a comfortable margin above the observed worst case.
Catching BudgetExceededException and retrying. Don't — you just spend the budget twice. Treat the exception as a failed run and surface it.

How cost is computed​

Reading total cost from the trace​

Capping spend with MaxBudgetUsd​

Budget events​

When the cost is $0.0000​

Common pitfalls​

See also​