Google: Gemma 4 31B (free)

// Node.js 18+ — set OPENROUTER_API_KEY in your environment
const res = await fetch('https://openrouter.ai/api/v1/chat/completions', {
  method: 'POST',
  headers: {
    'Authorization': `Bearer ${process.env.OPENROUTER_API_KEY}`,
    'Content-Type': 'application/json',
  },
  body: JSON.stringify({
    model: "google/gemma-4-31b-it:free",
    messages: [{ role: 'user', content: 'Hello' }],
  }),
});
const data = await res.json();
console.log(data);

# pip install requests
import json
import os
import requests

payload = {
    "model": "google/gemma-4-31b-it:free",
    "messages": [{"role": "user", "content": "Hello"}],
}
resp = requests.post(
    "https://openrouter.ai/api/v1/chat/completions",
    headers={
        "Authorization": f"Bearer {os.environ['OPENROUTER_API_KEY']}",
        "Content-Type": "application/json",
    },
    data=json.dumps(payload),
)
resp.raise_for_status()
print(resp.json())

package main

import (
	"bytes"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"os"
)

func main() {
	key := os.Getenv("OPENROUTER_API_KEY")
	payload := map[string]any{
		"model": "google/gemma-4-31b-it:free",
		"messages": []map[string]string{{"role": "user", "content": "Hello"}},
	}
	b, err := json.Marshal(payload)
	if err != nil {
		panic(err)
	}
	req, err := http.NewRequest(http.MethodPost, "https://openrouter.ai/api/v1/chat/completions", bytes.NewReader(b))
	if err != nil {
		panic(err)
	}
	req.Header.Set("Authorization", "Bearer "+key)
	req.Header.Set("Content-Type", "application/json")
	res, err := http.DefaultClient.Do(req)
	if err != nil {
		panic(err)
	}
	defer res.Body.Close()
	out, err := io.ReadAll(res.Body)
	if err != nil {
		panic(err)
	}
	fmt.Println(string(out))
}

import java.net.URI;
import java.net.http.HttpClient;
import java.net.http.HttpRequest;
import java.net.http.HttpResponse;

public class OpenRouterChat {
  public static void main(String[] args) throws Exception {
    String key = System.getenv("OPENROUTER_API_KEY");
    String body = "{\"model\":\"google/gemma-4-31b-it:free\",\"messages\":[{\"role\":\"user\",\"content\":\"Hello\"}]}";
    HttpRequest req = HttpRequest.newBuilder()
        .uri(URI.create("https://openrouter.ai/api/v1/chat/completions"))
        .header("Authorization", "Bearer " + key)
        .header("Content-Type", "application/json")
        .POST(HttpRequest.BodyPublishers.ofString(body))
        .build();
    HttpResponse<String> res = HttpClient.newHttpClient().send(req, HttpResponse.BodyHandlers.ofString());
    System.out.println(res.body());
  }
}

import java.net.URI
import java.net.http.HttpClient
import java.net.http.HttpRequest
import java.net.http.HttpResponse

fun main() {
    val key = System.getenv("OPENROUTER_API_KEY") ?: error("OPENROUTER_API_KEY")
    val body = "{\"model\":\"google/gemma-4-31b-it:free\",\"messages\":[{\"role\":\"user\",\"content\":\"Hello\"}]}"
    val req = HttpRequest.newBuilder()
        .uri(URI.create("https://openrouter.ai/api/v1/chat/completions"))
        .header("Authorization", "Bearer $key")
        .header("Content-Type", "application/json")
        .POST(HttpRequest.BodyPublishers.ofString(body))
        .build()
    val res = HttpClient.newHttpClient().send(req, HttpResponse.BodyHandlers.ofString())
    println(res.body())
}

// Cargo.toml: serde_json = "1", ureq = "2"
use serde_json::json;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let key = std::env::var("OPENROUTER_API_KEY")?;
    let model = "google/gemma-4-31b-it:free";
    let body = json!({
        "model": model,
        "messages": [{"role": "user", "content": "Hello"}]
    });
    let resp = ureq::post("https://openrouter.ai/api/v1/chat/completions")
        .set("Authorization", &format!("Bearer {}", key))
        .set("Content-Type", "application/json")
        .send_string(&body.to_string())?;
    println!("{}", resp.into_string()?);
    Ok(())
}

import java.net.URI
import java.net.http.{HttpClient, HttpRequest, HttpResponse}

@main def run(): Unit =
  val key = sys.env.getOrElse("OPENROUTER_API_KEY", throw new RuntimeException("OPENROUTER_API_KEY"))
  val body = "{\"model\":\"google/gemma-4-31b-it:free\",\"messages\":[{\"role\":\"user\",\"content\":\"Hello\"}]}"
  val req = HttpRequest.newBuilder()
    .uri(URI.create("https://openrouter.ai/api/v1/chat/completions"))
    .header("Authorization", s"Bearer $key")
    .header("Content-Type", "application/json")
    .POST(HttpRequest.BodyPublishers.ofString(body))
    .build()
  val res = HttpClient.newHttpClient().send(req, HttpResponse.BodyHandlers.ofString())
  println(res.body())
}

# macOS/Linux — set OPENROUTER_API_KEY in your environment
curl -sS 'https://openrouter.ai/api/v1/chat/completions' \
  -H "Authorization: Bearer $OPENROUTER_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"model":"google/gemma-4-31b-it:free","messages":[{"role":"user","content":"Hello"}]}'