# Multi-model API architecture: design one stable AI boundary

URL: https://infro.io/blog/multi-model-api-architecture
Author: INFRO Editorial (https://infro.io/blog/editorial)
Publisher: INFRO
Published: 2026-08-08
Last modified: 2026-09-11
Last reviewed: 2026-09-11 (next review due 2027-03-10)
Topic: Architecture and migration
Format: Brief

> A good multi-model API stabilizes authentication, request identity, common text semantics, errors, jobs, usage, and policy while exposing capability differences explicitly. It should prevent provider churn from leaking into product code without claiming every model behaves the same.

## Define the stable contract

Keep auth, project context, model identifiers, request IDs, timeout and cancellation behavior, common errors, usage fields, and metadata consistent. For text, an OpenAI-compatible surface reduces client work and supports existing SDKs.

Version incompatible changes and document provider-specific escape hatches. Silent semantic drift is worse than an explicit extension.

## Make capabilities discoverable

A catalog should expose modality, context limits, tool and structured-output support, job lifecycle, input types, pricing units, and current availability. The application or router can then reject impossible requests before paying provider latency.

Treat capability support as tested behavior, not a marketing label.

## Separate synchronous and asynchronous work

Streaming text and long-running video have different durability needs. Use a common job envelope for asynchronous work: create, status, cancel, result, signed webhook, usage, and error. Preserve direct streaming where it improves the experience.

Idempotency and stable job IDs matter because networks fail while expensive work continues.

## Keep routing and observation below the contract

Applications should express required capability and preferred model; infrastructure can apply health, cost, and fallback policy. Every decision should be traceable, and usage should be recorded once, in a form that can be compared with each provider's own invoice.

This boundary lets model policy evolve faster than application releases.

## Revision history

- 2026-09-11: Removed the promotional template sections and the generic FAQ, moved product context into the product section, and corrected product wording to the current BYOK model.