# Calling Any Model: Unified LLM Gateways & SDKs in 2026

> Why teams put a unified layer in front of LLM providers — and how LiteLLM, OpenRouter, and the Vercel AI SDK compare for fallback and cost control.

Don't hardwire one provider's SDK. A unified layer lets you switch models with a config change and adds fallback and cost control. Pick by form: the Vercel AI SDK for TypeScript app code, LiteLLM as a library or self-hosted proxy when you want to own the gateway, and OpenRouter as a hosted router with zero infrastructure. They compose — an SDK in the app, a gateway behind it.

Hardwiring one provider's SDK into your app is a decision you'll regret the first time that provider has an outage, raises prices, or ships a worse model than a competitor. A **unified model-access layer** fixes that: you call one interface, and switching or mixing models becomes a config change instead of a rewrite. It also buys you resilience (fallback) and control (central keys, cost tracking). This guide covers the layer and how the main options differ.

## What a unified layer gives you

- **No lock-in** — swap or mix providers/models by changing a string, not your code.
- **Resilience** — fall back to another provider when one is down or rate-limited.
- **Cost control** — central key management, per-team budgets, cost tracking, and caching.
- **One interface** — usually OpenAI-compatible, so most SDKs and code work unchanged.

## The options, by form factor

The three popular choices solve overlapping problems at different layers — that's the key to choosing.

### [Vercel AI SDK](/tools/vercel-ai-sdk) — the TypeScript app toolkit

Provider-agnostic calls plus streaming, structured output, tool calling, and UI hooks, in your application code. You get the "swap models freely" benefit and the building blocks for AI features. It's where your app *talks* to models — not an org-wide control plane. Best when you're building the app in TypeScript.

### [LiteLLM](/tools/litellm) — library or self-hosted proxy

Call 100+ models through one OpenAI-format interface as a **library**, or run its **proxy** as a self-hosted **gateway** with central keys, fallback, caching, cost tracking, and rate limits. Best when you want to **own** the gateway — for data control, custom policy, or on-prem.

### [OpenRouter](/tools/openrouter) — hosted router

A **managed** gateway: hundreds of models behind one API key and one bill, with routing and automatic fallback, and **no infrastructure to run**. Best when you want multi-provider access and resilience without operating a proxy.

## How to choose

- **Building a TS/JS app and want provider-agnostic calls + streaming/UI** → **Vercel AI SDK**.
- **Want to self-host the gateway (data control, policy, on-prem)** → **LiteLLM** (proxy).
- **Want a hosted gateway with zero ops** → **OpenRouter**.
- **Just one model, simple app** → a direct/provider-agnostic SDK; skip the gateway.

The important insight: **these compose.** A very common 2026 setup is the **Vercel AI SDK in the app** for ergonomics, with **LiteLLM or OpenRouter behind it** as the gateway for org-wide keys, fallback, and cost control. Add the resilience patterns (timeouts, retries, fallback) with the [provider-fallback-wrapper](/skills/api/provider-fallback-wrapper) skill, and let the [llm-integration-engineer](/agents/data-ai/llm-integration-engineer) wire the whole access layer.

> [!NOTE]
> A hosted router puts a third party in your request path — factor in its availability and that prompts pass through it. Self-hosting a proxy trades that for infrastructure you operate. Pick the trade that matches your constraints.

For making the responses themselves reliable once you can reach any model, see [Structured Output vs JSON Mode vs Function Calling](/guides/concepts/structured-output-2026).

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_Source: https://agentscamp.com/guides/concepts/calling-any-model-gateways — Guide on AgentsCamp._