Building With Multiple Frontier Models: A Practical Architecture Pattern

Building against multiple LLM providers sounds like it doubles your integration work — in practice, a well-designed abstraction layer makes it barely more effort than a single-provider integration, while giving you real resilience and cost control. Here's the pattern we implement.

The Three Layers

• Provider adapter layer — a thin, standardised interface (send prompt, get structured response, handle tool calls) implemented once per provider, isolating provider-specific API quirks from the rest of your application
• Routing layer — logic that picks which model handles a given request based on task type, cost budget, latency requirement, and current provider health, sitting between your application and the adapters
• Application layer — your actual product logic, written entirely against the routing layer's interface, with zero direct knowledge of which underlying model is serving any given request

What Makes This Pay Off, Not Just Add Complexity

The discipline that matters most is keeping prompts and tool definitions provider-agnostic wherever genuinely possible, and isolating the unavoidable provider-specific tuning inside the adapter layer rather than scattered through application code. Done well, swapping or adding a provider becomes a change contained to one adapter, not a hunt through your codebase for every place a specific API got called directly.

When Not to Bother

If you're a small team building a single-purpose tool with no meaningful cost sensitivity or resilience requirement, a direct single-provider integration is genuinely the right call — this pattern earns its complexity at a certain scale and stakes level, not below it. Build the abstraction when the cost of being locked to one provider actually threatens something (an outage, a pricing shock, a capability gap), not preemptively for its own sake.