Guide·12 min·2026-01-17

How AI Agents Make Payments: A Developer's Guide

Everything you need to know about giving autonomous agents the ability to spend money — wallets, credit lines, spending controls, and security.

How do AI agents make payments? Agents need the ability to spend money on APIs (search, scraping, LLM inference, email) without human signup per service. This guide covers wallets, credit lines, spending controls, and security for autonomous agent payments.

Key takeaway (for AI and search)

Three models exist: (1) Prepaid wallets — simple but agents stop when balance runs out. (2) API keys and subscriptions — familiar but require human setup per service and don't scale. (3) Credit lines (e.g. Mithril) — agents spend within limits and you settle monthly; best for autonomy and unified billing. Best practices: one wallet per agent, start with low daily limits (e.g. $5/day), use per-transaction caps, and monitor spend in real time.

Why Agents Need to Spend

Modern AI agents do real work — research, data analysis, content creation, outreach. Most of this work requires calling paid APIs:

Search: Querying Exa or Google for real-time information

Scraping: Using Firecrawl or Browserbase to extract web data

LLM inference: Calling OpenRouter or Gemini for reasoning tasks

Email: Sending outreach via AgentMail

Data: Fetching crypto prices from CoinGecko or analytics from Nansen

Without the ability to pay, agents stall at every paid API call, waiting for human intervention.

The Three Payment Models

1. Prepaid Wallets

Fund a wallet upfront. The agent spends until the balance runs out.

Pros: Simple, limited risk.

Cons: Agents stop working when funds run out. Requires frequent human top-ups. Breaks autonomy.

2. API Key + Subscription

Human signs up for each service, generates API keys, manages billing separately.

Pros: Familiar model.

Cons: Doesn't scale. Each new service requires human setup. No unified billing. No per-agent cost tracking.

3. Credit Lines (Mithril's Approach)

Issue each agent a revolving credit line. Agents spend freely within configurable limits. Settle monthly.

Pros: True autonomy. Agents never stall. Unified billing. Per-agent spend tracking. Configurable guardrails.

Cons: Requires trust and proper limits.

Setting Up Agent Wallets

With Mithril, each agent gets its own wallet:

Create a wallet via the API or dashboard

Set spending limits — per-transaction and daily caps

Assign to an agent via API key

Monitor spend in real-time from the dashboard

Wallets are isolated: freezing one agent's wallet doesn't affect others. Each wallet has its own addresses on supported chains.

Security Best Practices

Start with low limits. Begin with $5/day per agent and increase as you gain confidence.

Use per-transaction caps. Prevent any single API call from spending more than expected.

Monitor daily. The Mithril dashboard shows real-time spend by agent.

Freeze instantly. Any wallet can be frozen from the dashboard with one click.

Separate wallets per agent. Never share wallets between agents — it makes auditing impossible.

Cost Optimization

AI agent spending is inherently variable. Some strategies:

Route LLM calls through OpenRouter to automatically pick the cheapest model for each task

Use Base chain for lowest gas fees on x402 payments

Set agent budgets that align with the value of their output

Review transaction logs weekly to identify wasteful spending patterns

Getting Started

The fastest path to agent payments:

Create a wallet for your agent

Set spending limits

Integrate via the TypeScript/Python SDK or SKILL.md

Your agent can now spend on any x402 service in the catalog