Models

Applications depend on the small ModelGateway contract, never on a vendor SDK directly. A gateway streams output.delta fragments followed by exactly one completed event.

The ModelGateway contract

import type { ModelGateway } from '@fevex/core/models';

export const model: ModelGateway = {
  async *stream(input) {
    for await (const event of yourProvider.stream(input)) {
      if (event.type === 'text.delta') {
        yield { type: 'output.delta', delta: event.text };
      } else if (event.type === 'completed') {
        yield { type: 'completed', result: { output: event.output } };
      }
    }
  },
};

FEVEX rejects a missing or duplicate terminal, post-terminal events, and a final output that does not match the accumulated deltas.

Official adapters

Official adapters implement this contract for you:

import { createOpenAI } from '@fevex/openai';

const model = createOpenAI({ apiKey: process.env.OPENAI_API_KEY! })('gpt-5.6');

DeepSeek follows the same shape:

import { createDeepSeek } from '@fevex/deepseek';

const model = createDeepSeek({
  apiKey: process.env.DEEPSEEK_API_KEY!,
})('deepseek-v4-flash');

Structured output is only parsed as JSON and validated when the agent declares an outputSchema; otherwise model text is preserved exactly as a string.