Account-free, pay-per-use API gateways are middleware that let AI agents call external services on demand without requiring end users to create separate downstream accounts or long-lived credentials. These gateways bill per call or per byte, broker authentication, and enforce request policies while presenting a uniform endpoint to agents. The model addresses two concurrent trends in 2026: widespread autonomous agents that need frictionless, programmatic access to many third‑party APIs, and the move to usage-based, serverless consumption models that avoid subscription lock‑in. Key components include standardized context bridges such as the Model Context Protocol (MCP), hosted MCP servers (Cloudflare’s MCP servers and AWS’s specialized MCP servers) that expose capabilities like Workers/KV/R2/D1 or AWS services, and integration platforms like Pipedream that provide connectors to thousands of APIs and a hosted runtime for custom transformations. Together these tools let an agent call a single gateway (e.g., Pay.sh or a self-hosted alternative), which then routes, authenticates, meters, and bills for each action while logging provenance and applying policy. This pattern is timely because agent deployments increasingly demand low-friction integration, finer-grained cost controls, and stronger auditability. Gateways reduce developer and user onboarding friction, enable per-request billing, and centralize rate-limiting and compliance controls. Trade-offs remain: privacy and data residency, abuse prevention, latency from brokered calls, and dependency on gateway operators. Practical alternatives range from managed pay-per-use gateways to composing Cloudflare Workers, Pipedream integrations, or AWS MCP servers into a hybrid solution that balances control, coverage, and cost. For architects, the choice is now between convenience and operational transparency when enabling agent-driven access to the web of APIs.