If you want to use Gemini’s public API, but at the same time have a safe fallback in case you have exhausted the rate limits, you can use the OpenAI TS/JS library and a few helper functions. In my particular case I needed a type-safe solution for a chartmaker app with a fallback since Gemini’s gemini-2.5-pro-exp-03-25 model is restricted to 20 request/min.
First, you need to define which models you want to use so that they appear as autosuggest when you use the helper functions:
type Model = ChatCompletionParseParams['model'] | 'gemini-2.5-pro-exp-03-25' | 'gemini-2.0-flash';
The helper function requires one argument; an array of 2 configuration objects for the desired AI queries (in principle, you can add as many as you want, or choose other AIs that are compatible with the OpenAI library):
export const getCompletion = async (
options: [
Omit<ChatCompletionParseParams, 'model'> & { model: Model },
Omit<ChatCompletionParseParams, 'model'> & { model: Model },
],
) => {
try {
const isGemini = options[0].model.includes('gemini');
const openai = new OpenAI(
isGemini
? {
apiKey: process.env.GEMINI_API_KEY,
baseURL: 'https://generativelanguage.googleapis.com/v1beta/openai/',
}
: { apiKey: process.env.OPENAI_API_KEY },
);
return await openai.chat.completions.create(options[0]);
} catch (error) {
console.log(`Failed completion for first model (${options[0].model})`, error);
const isGemini = options[1].model.includes('gemini');
const openai = new OpenAI(
isGemini
? {
apiKey: process.env.GEMINI_API_KEY,
baseURL: 'https://generativelanguage.googleapis.com/v1beta/openai/',
}
: { apiKey: process.env.OPENAI_API_KEY },
);
return await openai.chat.completions.create(options[1]);
}
};
The help function can be used in the following ways:
const messages = [{ role: 'user', content: 'Tell a short joke.' }];
const completion = await getCompletion([
{ model: 'gemini-2.0-flash', messages },
{ model: 'gpt-3.5-turbo', messages },
]);
console.log(completion);
// {
// "choices": [
// {
// "finish_reason": "stop",
// "index": 0,
// "message": {
// "content": "Why don't scientists trust atoms?\n\nBecause they make up everything!\n",
// "role": "assistant"
// }
// }
// ],
// "created": 1743757243,
// "model": "gemini-2.0-flash",
// "object": "chat.completion",
// "usage": {
// "completion_tokens": 16,
// "prompt_tokens": 5,
// "total_tokens": 21
// }
// }
You can also create a helper function for type-safe structured output:
export const getJSONCompletion = async <T>(
options: [
Omit<ChatCompletionParseParams, 'model'> & { model: Model },
Omit<ChatCompletionParseParams, 'model'> & { model: Model },
],
): Promise<ParsedChatCompletion<T> & { _request_id?: string | null | undefined }> => {
try {
const isGemini = options[0].model.includes('gemini');
const openai = new OpenAI(
isGemini
? {
apiKey: process.env.GEMINI_API_KEY,
baseURL: 'https://generativelanguage.googleapis.com/v1beta/openai/',
}
: { apiKey: process.env.OPENAI_API_KEY },
);
return await openai.beta.chat.completions.parse({ ...options[0] });
} catch (error) {
console.log('Failed completion for first model', error);
const isGemini = options[1].model.includes('gemini');
const openai = new OpenAI(
isGemini
? {
apiKey: process.env.GEMINI_API_KEY,
baseURL: 'https://generativelanguage.googleapis.com/v1beta/openai/',
}
: { apiKey: process.env.OPENAI_API_KEY },
);
return await openai.beta.chat.completions.parse({ ...options[1] });
}
};
It can be used in the following way:
import z from 'zod';
//... Omitted for brevity
const messages = [{ role: "user", content: "Your instructions..."}] satisfies ChatCompletionMessageParam[];
const format = z.object({ customizations: z.array(z.string()) });
const responseFormat = zodResponseFormat(format, 'chart-customizations');
const completion = await getJSONCompletion<z.infer<typeof format>>(
[
{ model: 'gemini-2.5-pro-exp-03-25', response_format: responseFormat, messages, temperature: 0 },
{ model: 'o3-mini-2025-01-31', reasoning_effort: 'high', response_format: responseFormat, messages },
],
);
const customizationsArr = completion.choices[0].message.parsed?.customizations;