Pay-per-use, account-free API gateways let developers and AI agents access multiple language and multimodal models without requiring direct accounts at each provider. These gateways provide an OpenAI‑compatible surface, routing, metering and single‑payer billing so agent marketplaces, agent frameworks, and tool marketplaces can compose, broker, and monetize agent behaviors with per‑call pricing. The model ecosystem in 2026 emphasizes composability and cost transparency: tools such as AskCodi offer OpenAI‑compatible API layers and routing across custom and public models, enabling agents to call the best model for a task. Specialty endpoints—Perplexity’s web‑grounded answer APIs and Phind’s developer search—illustrate how gateways combine retrieval and grounding with generative models. Major model families (Google Gemini, Anthropic’s Claude) remain behind provider APIs; gateways abstract these into unified interfaces. Amazon’s CodeWhisperer/ Q Developer lineage shows how domain‑specific assistants (coding) are integrated into broader developer platforms accessed via gateways. Relevance is driven by lowered friction for marketplaces and frameworks: pay‑per‑use billing reduces onboarding overhead for end users and enables microtransactions for agent capabilities, while account‑free flows avoid requiring every integrator to manage multiple provider contracts. Key considerations when adopting these gateways include latency, cost allocation, data residency, provenance and citation (especially for web‑grounded outputs), API compatibility, and security/compliance. In short, pay‑per‑use, account‑free gateways are a practical middle layer that balances developer convenience, model choice, and monetization for agent ecosystems—but they require clear SLAs, transparent pricing, and careful data governance to be effective in production.