Model Adapter (OpenAI / Gemini)

createOpenAIAdapter (@rejelly/adapter-openai) and createGeminiAdapter (@rejelly/adapter-gemini) wrap provider models into Rejelly's ModelAdapter and deliver the JSON Schema from promptAgent(schema) to the underlying model.

For the send-side contract of multimodal tool results, see Adapter · Multimodal Tool Results.

Creating a Model Adapter

OpenAI

import { createOpenAIAdapter } from '@rejelly/adapter-openai';

const model = createOpenAIAdapter({
  modelId: 'gpt-5.6-luna',
  apiKey: process.env.OPENAI_API_KEY,
  schemaMode: 'json_schema',
});

createOpenAIAdapter also works with OpenAI-compatible providers:

import { createOpenAIAdapter } from '@rejelly/adapter-openai';

const model = createOpenAIAdapter({
  id: 'deepseek-chat',
  provider: 'deepseek',
  modelId: 'deepseek-chat',
  apiKey: process.env.DEEPSEEK_API_KEY,
  baseURL: 'https://api.deepseek.com',
  schemaMode: 'json_object',
  chatCompletionParams: {
    temperature: 0.2,
  },
  requestOption: {
    timeout: 60_000,
  },
});

Gemini

import { createGeminiAdapter } from '@rejelly/adapter-gemini';

const model = createGeminiAdapter({
  modelId: 'gemini-2.5-pro',
  apiKey: process.env.GEMINI_API_KEY,
  schemaMode: 'json_schema',
});

In Node environments, if apiKey is not explicitly passed, Gemini reads GEMINI_API_KEY or GOOGLE_API_KEY; in browser environments, it should be passed explicitly. Use generateContentParams to forward Gemini request parameters:

import { createGeminiAdapter } from '@rejelly/adapter-gemini';

const model = createGeminiAdapter({
  modelId: 'gemini-2.5-flash',
  schemaMode: 'prompt',
  generateContentParams: {
    temperature: 0.3,
  },
});

Using in an Agent

The created object is a Rejelly ModelAdapter and can be passed directly to createAgent({ model }), or injected uniformly via runWith's model registry.

import { createAgent, promptAgent } from '@rejelly/core';
import { createOpenAIAdapter } from '@rejelly/adapter-openai';
import { z } from 'zod';

const model = createOpenAIAdapter({
  modelId: 'gpt-5.6-luna',
  apiKey: process.env.OPENAI_API_KEY,
});

const AnswerSchema = z.object({
  answer: z.string(),
});

export const AnswerAgent = createAgent({
  id: 'answer',
  model,
  handler: async () => {
    return await promptAgent(AnswerSchema);
  },
});

Cost Calculation

To have the Budget mechanism record real costs, provide calculateCost on the adapter. Return values use integer units, e.g., micro_usd.

import { createOpenAIAdapter } from '@rejelly/adapter-openai';

const model = createOpenAIAdapter({
  modelId: 'gpt-5.6-luna',
  apiKey: process.env.OPENAI_API_KEY,
  calculateCost: (usage) => ({
    micro_usd:
      Math.ceil(usage.promptTokens * 1) +
      Math.ceil(usage.completionTokens * 6),
  }),
});

Prompt Schema Injection

Choose the schema delivery method via schemaMode:

• "prompt"：Injects the schema into the system prompt — broadest compatibility (OpenAI default).
• "json_object"：Sends response_format: { type: "json_object" } (Gemini: responseMimeType: "application/json"), while also injecting the schema into the prompt for field constraints. Suitable for models with JSON mode but without strict schema support (e.g., DeepSeek).
• "json_schema"：Native Structured Outputs (OpenAI strict / Gemini responseSchema), where the model strictly enforces fields (Gemini default).