Per-Model Type Safety

The AI SDK provides model-specific type safety for modelOptions. Each model's capabilities determine which model options are allowed, and TypeScript will enforce this at compile time.

Tip: For structured outputs, most users should prefer the first-class chat({ outputSchema }) option over the raw provider text option shown below — it works across providers and validates the result for you. The raw text option is for when you need provider-specific control.

How It Works#

Each adapter factory captures the model literal as a type parameter — openaiText<TModel>(model) — so the adapter carries the exact model you selected at the type level.

The modelOptions you pass are then resolved against a per-model map (ResolveProviderOptions<TModel>). Each model's entry declares only the options that model actually supports. A model without a structured-output capability simply has no text property in its resolved options type, so TypeScript's excess-property checking rejects text for that model — at compile time, with zero runtime cost.

This is the same mechanism described in Typed Pre-Configured Options (which captures these resolved options in a reusable object) and Extend Adapter (which lets you attach the same typed modelOptions to custom models).

Usage Examples#

✅ Correct Usage#

import { chat } from "@tanstack/ai";
import { openaiText } from "@tanstack/ai-openai";

// ✅ gpt-5 supports structured outputs - `text` is allowed
const validCall = chat({
  adapter: openaiText("gpt-5"),
  messages: [],
  modelOptions: {
    // OK - text is included for gpt-5
    text: {
      format: {
        type: "json_schema",
        name: "my_schema",
        schema: {
          /* JSON Schema object */
        },
      },
    },
  },
});

❌ Incorrect Usage#

// ❌ gpt-4-turbo does NOT support structured outputs - `text` is rejected
const invalidCall = chat({
  adapter: openaiText("gpt-4-turbo"),
  messages: [],
  modelOptions: {
    text: {}, // ❌ TypeScript error: 'text' does not exist in type
  },
});

TypeScript will produce:

error TS2353: Object literal may only specify known properties, and 'text' does not exist in type ...'.

Benefits#

• Compile-time safety: Catch incorrect model options before deployment
• Better IDE experience: Autocomplete shows only valid options for each model
• Self-documenting: Model capabilities are explicit in the type system
• Zero runtime overhead: All type checking happens at compile time