Cost Control

You’ve instrumented your application and can see every LLM call. Now let’s add the safety rails that prevent a single bug from draining your budget.

Why Cost Control Matters

If you’ve ever woken up to a surprise $500 bill from OpenAI, you know the pain. Unlike traditional software where costs are predictable, AI applications have a hidden danger: a single bug or bad prompt can drain your budget in minutes. Imagine this: your AI agent gets stuck in a loop, calling GPT-4 thousands of times. By the time you notice, the damage is done. Traditional usage alerts from LLM providers arrive too late—sometimes hours after the spending happened. Aden acts as a speed bump between your code and the LLM API. It tracks every call in real-time and can automatically take action before costs spiral out of control.

The Four Actions

Aden gives you four levels of protection, from gentle warnings to hard stops:

Alert

Send notifications when spending reaches warning thresholds. Your code keeps running, but you know something needs attention.

Throttle

Add delays between requests to slow the burn rate. Gives you time to investigate without completely stopping your users.

Degrade

Automatically switch to cheaper models. Your users still get answers, you save money.

Block

Hard stop when budget is exhausted. The most effective cost-cutting action—stops the bleeding immediately.

Configuring Budgets on the Server

The SDK enforces budgets that you configure on the Aden control server. When your application starts, it connects to the server and receives the current policy. All enforcement happens locally—no per-request latency added.

Budget Threshold Progression

Configure thresholds to trigger different actions as spending increases:

0% ─────────── 50% ─────────── 80% ─────────── 95% ─────────── 100%
   [ALLOW]       [ALERT]        [DEGRADE]       [THROTTLE]      [BLOCK]
                   │                │                │              │
                   ↓                ↓                ↓              ↓
              "Warning!"      Switch to        Slow down       Hard stop
                            gpt-4o-mini

Server-Side Configuration

Configure budgets via the Aden dashboard or API. Here’s an example policy with multiple thresholds:

Budget Policy

{
  "type": "global",
  "limit_usd": 100.00,
  "thresholds": [
    {"percent": 50, "action": "alert", "level": "warning"},
    {"percent": 80, "action": "degrade", "provider": "openai", "to_model": "gpt-4o-mini"},
    {"percent": 95, "action": "throttle", "delay_ms": 2000}
  ],
  "limit_action": "block"
}

Show API Endpoints

Endpoint	Method	Description
`/v1/control/policy/budgets`	POST	Create or update budget limits
`/v1/control/policy/alerts`	POST	Configure alert thresholds
`/v1/control/policy/degradations`	POST	Set up model degradation rules
`/v1/control/policy/throttles`	POST	Configure throttling rules

What Happens in Your App

Once budgets are configured on the server, your SDK automatically enforces them:

// At $0 spent (0% of $100 budget)
await openai.chat.completions.create({ model: "gpt-4o", ... });
// → Uses gpt-4o ✓

// At $50 spent (50% of budget)
await openai.chat.completions.create({ model: "gpt-4o", ... });
// → Uses gpt-4o, triggers onAlert callback with "warning"

// At $80 spent (80% of budget)
await openai.chat.completions.create({ model: "gpt-4o", ... });
// → Automatically uses gpt-4o-mini instead (degraded)

// At $95 spent (95% of budget)
await openai.chat.completions.create({ model: "gpt-4o", ... });
// → Uses gpt-4o-mini, request delayed 2 seconds (throttled)

// At $100+ spent (100% of budget)
await openai.chat.completions.create({ model: "gpt-4o", ... });
// → Throws RequestCancelledError (blocked)

The SDK caches the policy locally and syncs with the server periodically. This means zero latency overhead on each request while still getting real-time budget updates.

Setting Up Alerts

Get notified before it’s too late. Alerts let you know when you’re approaching budget limits—not hours later, but in real-time.

Server-Side Alert Policy

Configure alert thresholds via the Aden dashboard or API:

Alert Configuration

[
  {
    "trigger": "budget_threshold",
    "threshold_percent": 80,
    "level": "warning",
    "message": "Approaching budget limit"
  },
  {
    "trigger": "budget_threshold",
    "threshold_percent": 95,
    "level": "critical",
    "message": "Budget nearly exhausted"
  }
]

SDK Alert Handler

When alerts trigger, your onAlert callback receives the notification:

TypeScript
Python

import { instrument } from "aden-ts";
import OpenAI from "openai";

await instrument({
  apiKey: process.env.ADEN_API_KEY,
  serverUrl: process.env.ADEN_API_URL,
  sdks: { OpenAI },

  // This runs whenever an alert triggers
  onAlert: (alert) => {
    console.warn(`[${alert.level}] ${alert.message}`);

    if (alert.level === "warning") {
      sendSlackMessage(`Budget warning: ${alert.message}`);
    } else if (alert.level === "critical") {
      sendPagerDutyAlert(`URGENT: ${alert.message}`);
    }
  },
});

// Use your LLM normally - alerts trigger automatically
const openai = new OpenAI();
const response = await openai.chat.completions.create({
  model: "gpt-4o",
  messages: [{ role: "user", content: "Hello!" }],
});

import os
import asyncio
from aden import instrument_async, uninstrument_async, MeterOptions

def handle_alert(alert):
    print(f"[{alert.level}] {alert.message}")

    if alert.level == "warning":
        send_slack_message(f"Budget warning: {alert.message}")
    elif alert.level == "critical":
        send_pagerduty_alert(f"URGENT: {alert.message}")

async def main():
    await instrument_async(MeterOptions(
        api_key=os.environ.get("ADEN_API_KEY"),
        server_url=os.environ.get("ADEN_API_URL"),
        on_alert=handle_alert,
    ))

    from openai import AsyncOpenAI
    client = AsyncOpenAI()

    # Use your LLM normally - alerts trigger automatically
    response = await client.chat.completions.create(
        model="gpt-4o",
        messages=[{"role": "user", "content": "Hello!"}],
    )

    await uninstrument_async()

asyncio.run(main())

Throttling Runaway Agents

Alerts are great, but what if you want the system to automatically slow down? Throttling adds delays to requests when approaching limits—your agent keeps working, just more slowly.

Server-Side Throttle Policy

Configure throttling thresholds via the Aden dashboard or API:

Throttle Configuration

[
  {
    "trigger": "budget_threshold",
    "threshold_percent": 90,
    "delay_ms": 2000
  },
  {
    "trigger": "budget_threshold",
    "threshold_percent": 95,
    "delay_ms": 5000
  }
]

What Happens

Normal operation:    Request → Response → Request → Response
                        ↓         ↓          ↓         ↓
                       0ms       0ms        0ms       0ms

At 90% budget:       Request → [2 sec wait] → Response → Request → [2 sec wait] → Response
                                    ↓                         ↓
                                 Slower,                   but still
                                 but working               working!

Throttling gives you time to investigate without completely stopping your users. Think of it like a speed limiter in a car.

SDK Implementation

The SDK automatically enforces throttling. Your code stays the same:

TypeScript
Python

import { instrument } from "aden-ts";
import OpenAI from "openai";

await instrument({
  apiKey: process.env.ADEN_API_KEY,
  serverUrl: process.env.ADEN_API_URL,
  sdks: { OpenAI },
});

const openai = new OpenAI();

// At 90% budget, this request will automatically wait 2 seconds
// Your code doesn't change at all - Aden handles it
const response = await openai.chat.completions.create({
  model: "gpt-4o",
  messages: [{ role: "user", content: "Generate a report" }],
});

import os
import asyncio
from aden import instrument_async, uninstrument_async, MeterOptions

async def main():
    await instrument_async(MeterOptions(
        api_key=os.environ.get("ADEN_API_KEY"),
        server_url=os.environ.get("ADEN_API_URL"),
    ))

    from openai import AsyncOpenAI
    client = AsyncOpenAI()

    # At 90% budget, this request will automatically wait 2 seconds
    # Your code doesn't change at all - Aden handles it
    response = await client.chat.completions.create(
        model="gpt-4o",
        messages=[{"role": "user", "content": "Generate a report"}],
    )

    await uninstrument_async()

asyncio.run(main())

Automatic Model Degradation

This is one of the most powerful features. When approaching your budget, why pay premium prices? Aden can automatically switch to a cheaper model—your users still get answers, and you save money.

Server-Side Degradation Policy

Configure model degradation rules via the Aden dashboard or API:

Degradation Configuration

[
  {
    "provider": "openai",
    "from_model": "gpt-4o",
    "to_model": "gpt-4o-mini",
    "trigger": "budget_threshold",
    "threshold_percent": 50
  },
  {
    "provider": "anthropic",
    "from_model": "claude-3-5-sonnet-latest",
    "to_model": "claude-3-5-haiku-latest",
    "trigger": "budget_threshold",
    "threshold_percent": 80
  }
]

What Happens

Budget at 0-50%:     "gpt-4o"  →  Full power, highest quality
Budget at 50-100%:   "gpt-4o-mini"  →  Cheaper, still good for most tasks
Budget exceeded:     [blocked]  →  No more requests

The magic is that your code still asks for gpt-4o—Aden silently swaps it to the cheaper model behind the scenes.

Model degradation keeps your application running without any code changes. Your users get answers, your wallet stays happy.

SDK Implementation

Your code stays the same—the SDK handles the model swap automatically:

TypeScript
Python

import { instrument } from "aden-ts";
import OpenAI from "openai";

await instrument({
  apiKey: process.env.ADEN_API_KEY,
  serverUrl: process.env.ADEN_API_URL,
  sdks: { OpenAI },
});

const openai = new OpenAI();

// Early in the month (0% budget used)
await openai.chat.completions.create({
  model: "gpt-4o",  // You ask for gpt-4o
  messages: [{ role: "user", content: "Quick question" }],
});
// → Uses gpt-4o ✓ (full quality)

// Later (50%+ budget used)
await openai.chat.completions.create({
  model: "gpt-4o",  // You still ask for gpt-4o
  messages: [{ role: "user", content: "Another question" }],
});
// → Automatically uses gpt-4o-mini instead (cheaper!)

import os
import asyncio
from aden import instrument_async, uninstrument_async, MeterOptions

async def main():
    await instrument_async(MeterOptions(
        api_key=os.environ.get("ADEN_API_KEY"),
        server_url=os.environ.get("ADEN_API_URL"),
    ))

    from openai import AsyncOpenAI
    client = AsyncOpenAI()

    # Your code always asks for the premium model
    response = await client.chat.completions.create(
        model="gpt-4o",
        messages=[{"role": "user", "content": "Help me with this task"}],
    )
    # Aden may have used gpt-4o-mini behind the scenes
    # Your app keeps working, costs stay under control

    await uninstrument_async()

asyncio.run(main())

Blocking: The Emergency Stop

Sometimes you need to just stop. When your budget is exhausted, Aden can block requests entirely. This is your emergency stop button—it stops the bleeding immediately.

Server-Side Budget Limit

Configure the action when budget is exhausted:

Budget with Block Action

{
  "type": "global",
  "limit_usd": 100.00,
  "limit_action": "block"
}

When the budget hits 100%, any new LLM request fails with a RequestCancelledError. The request never reaches OpenAI/Anthropic, so you don’t get charged.

Make sure your application handles RequestCancelledError gracefully. Show users a friendly message like “You’ve reached your usage limit” rather than crashing.

SDK Implementation

TypeScript
Python

import { instrument, RequestCancelledError } from "aden-ts";
import OpenAI from "openai";

await instrument({
  apiKey: process.env.ADEN_API_KEY,
  serverUrl: process.env.ADEN_API_URL,
  sdks: { OpenAI },
  getContextId: () => getCurrentUserId(),  // Track per-user
});

const openai = new OpenAI();

try {
  const response = await openai.chat.completions.create({
    model: "gpt-4o",
    messages: [{ role: "user", content: "Hello!" }],
  });
  console.log(response.choices[0].message.content);
} catch (error) {
  if (error instanceof RequestCancelledError) {
    // Budget exhausted - request blocked BEFORE reaching OpenAI
    showUserMessage(
      "You've reached your usage limit. " +
      "Upgrade your plan to continue using AI features."
    );
  } else {
    throw error;
  }
}

import os
import asyncio
from aden import instrument_async, MeterOptions, RequestCancelledError

async def main():
    await instrument_async(MeterOptions(
        api_key=os.environ.get("ADEN_API_KEY"),
        server_url=os.environ.get("ADEN_API_URL"),
    ))

    from openai import AsyncOpenAI
    client = AsyncOpenAI()

    try:
        response = await client.chat.completions.create(
            model="gpt-4o",
            messages=[{"role": "user", "content": "Hello!"}],
        )
        print(response.choices[0].message.content)

    except RequestCancelledError as e:
        # Budget exhausted - request blocked BEFORE reaching OpenAI
        show_user_message(
            "You've reached your usage limit. "
            "Please upgrade your plan to continue."
        )

asyncio.run(main())

Granular Budgets

Instead of one big budget for your whole organization, set separate budgets for different customers, features, agents, or custom tags.

Why granular budgets matter

Without granular budgets:

One big budget: $1000
                  ↓
Customer A uses $950 (they went wild!)
                  ↓
Customer B, C, D... all blocked (unfair!)

With Aden’s granular budgets:

Global budget: $1000 (safety net)
├── Customer A: $100 budget → blocked at $100 (fair!)
├── Customer B: $100 budget → still has full $100
├── Customer C: $50 budget  → smaller customer, smaller budget
└── ... each customer isolated

Server-Side Budget Configuration

Configure multiple budget types via the Aden dashboard or API:

Multi-Budget Configuration

[
  {
    "type": "global",
    "limit_usd": 1000.00,
    "limit_action": "block"
  },
  {
    "type": "customer",
    "match_value": "acme-corp",
    "limit_usd": 100.00,
    "limit_action": "block"
  },
  {
    "type": "feature",
    "match_value": "document-analysis",
    "limit_usd": 500.00,
    "limit_action": "degrade",
    "provider": "openai",
    "degrade_to": "gpt-4o-mini"
  }
]

Budget Types

Type	Matches On	Use Case
Global	All requests	Organization-wide safety net
Customer	`metadata.customer`	Multi-tenant SaaS apps
Agent	`metadata.agent`	Different AI agent tiers
Feature	`metadata.feature`	Chat vs. document analysis
Tag	`metadata.tag`	Projects, teams, anything else

When a request matches multiple budgets, all are validated and the most restrictive action wins.

SDK Implementation

TypeScript
Python

import { instrument, enterMeterContext } from "aden-ts";
import OpenAI from "openai";

await instrument({
  apiKey: process.env.ADEN_API_KEY,
  serverUrl: process.env.ADEN_API_URL,
  sdks: { OpenAI },
});

const openai = new OpenAI();

// In your API route, set the context
app.post("/analyze-document", async (req, res) => {
  enterMeterContext({
    metadata: {
      customer: req.user.companyId,     // "acme-corp"
      feature: "document-analysis",
    },
  });

  // This request is validated against:
  // 1. Global budget ($1000)
  // 2. Acme-corp's customer budget ($100)
  // 3. Document-analysis feature budget ($500)
  // Most restrictive wins!

  const response = await openai.chat.completions.create({
    model: "gpt-4o",
    messages: [{ role: "user", content: `Analyze: ${req.body.document}` }],
  });
});

import os
from aden import instrument_async, MeterOptions

async def main():
    await instrument_async(MeterOptions(
        api_key=os.environ.get("ADEN_API_KEY"),
        server_url=os.environ.get("ADEN_API_URL"),
    ))

    from openai import AsyncOpenAI
    client = AsyncOpenAI()

    # Tag the request with metadata for budget matching
    response = await client.chat.completions.create(
        model="gpt-4o",
        messages=[{"role": "user", "content": "Analyze this document..."}],
        extra_body={
            "metadata": {
                "customer": "acme-corp",
                "feature": "document-analysis",
            }
        },
    )

    # Validated against multiple budgets:
    # - Global budget ($1000)
    # - Acme-corp's customer budget ($100)
    # - Document-analysis feature budget ($500)

Fail Open for Resilience

What happens if Aden’s control server goes down? By default, Aden “fails open”—requests proceed normally, ensuring your application stays available.

Fail-open means your users never see downtime due to Aden. You’ll get an alert about the connectivity issue, but your app keeps working.

TypeScript
Python

import { instrument } from "aden-ts";
import OpenAI from "openai";

await instrument({
  apiKey: process.env.ADEN_API_KEY,
  serverUrl: process.env.ADEN_API_URL,
  sdks: { OpenAI },

  failOpen: true,  // Default - requests proceed if server unreachable

  onAlert: (alert) => {
    if (alert.message.includes("server unreachable")) {
      console.warn("Aden server down - operating without cost controls");
      notifyOpsTeam("Aden server unreachable");
    }
  },
});

// Even if Aden's server is down, your app keeps working
const openai = new OpenAI();
const response = await openai.chat.completions.create({
  model: "gpt-4o",
  messages: [{ role: "user", content: "Hello!" }],
});

import os
from aden import instrument_async, MeterOptions

async def main():
    await instrument_async(MeterOptions(
        api_key=os.environ.get("ADEN_API_KEY"),
        server_url=os.environ.get("ADEN_API_URL"),
        fail_open=True,  # Default - requests proceed if unreachable
        on_alert=lambda alert: print(f"Alert: {alert.message}"),
    ))

    from openai import AsyncOpenAI
    client = AsyncOpenAI()

    # Your app keeps working even if Aden's server is down
    response = await client.chat.completions.create(
        model="gpt-4o",
        messages=[{"role": "user", "content": "Hello!"}],
    )

Quick Reference

Action Summary

Action	When to Use	What Happens
Alert	Early warning (80%)	Notification sent, request proceeds
Throttle	Slow down (90%)	Request delayed, then proceeds
Degrade	Save money (50%)	Cheaper model used automatically
Block	Hard stop (100%)	Request fails with error

Budget Hierarchy

Budget Type	Example	Use For
Global	$1000/month	Organization-wide safety net
Customer	$100/customer	Multi-tenant fairness
Agent	$200/agent-type	Tiered pricing
Feature	$500/feature	Feature-level tracking
Tag	Custom	Teams, projects

Error Handling

Always catch RequestCancelledError to handle blocked requests gracefully:

try {
  await openai.chat.completions.create({ ... });
} catch (error) {
  if (error instanceof RequestCancelledError) {
    showUserMessage("Usage limit reached");
  }
}

Getting Started

Use Cases

TypeScript SDK

Python SDK

Why Cost Control Matters

The Four Actions

Alert

Throttle

Degrade

Block

Configuring Budgets on the Server

Budget Threshold Progression

Server-Side Configuration

What Happens in Your App

Setting Up Alerts

Server-Side Alert Policy

SDK Alert Handler

Throttling Runaway Agents

Server-Side Throttle Policy

What Happens

SDK Implementation

Automatic Model Degradation

Server-Side Degradation Policy

What Happens

SDK Implementation

Blocking: The Emergency Stop

Server-Side Budget Limit

SDK Implementation

Granular Budgets

Why granular budgets matter

Server-Side Budget Configuration

Budget Types

SDK Implementation

Fail Open for Resilience

Quick Reference

Next Steps

TypeScript SDK

Python SDK

Getting Started

Use Cases

TypeScript SDK

Python SDK

​Why Cost Control Matters

​The Four Actions

Alert

Throttle

Degrade

Block

​Configuring Budgets on the Server

​Budget Threshold Progression

​Server-Side Configuration

​What Happens in Your App

​Setting Up Alerts

​Server-Side Alert Policy

​SDK Alert Handler

​Throttling Runaway Agents

​Server-Side Throttle Policy

​What Happens

​SDK Implementation

​Automatic Model Degradation

​Server-Side Degradation Policy

​What Happens

​SDK Implementation

​Blocking: The Emergency Stop

​Server-Side Budget Limit

​SDK Implementation

​Granular Budgets

​Why granular budgets matter

​Server-Side Budget Configuration

​Budget Types

​SDK Implementation

​Fail Open for Resilience

​Quick Reference

​Next Steps

TypeScript SDK

Python SDK

Why Cost Control Matters

The Four Actions

Configuring Budgets on the Server

Budget Threshold Progression

Server-Side Configuration

What Happens in Your App

Setting Up Alerts

Server-Side Alert Policy

SDK Alert Handler

Throttling Runaway Agents

Server-Side Throttle Policy

What Happens

SDK Implementation

Automatic Model Degradation

Server-Side Degradation Policy

What Happens

SDK Implementation

Blocking: The Emergency Stop

Server-Side Budget Limit

SDK Implementation

Granular Budgets

Why granular budgets matter

Server-Side Budget Configuration

Budget Types

SDK Implementation

Fail Open for Resilience

Quick Reference

Next Steps