How to call an OpenRouter LLM with the official Ruby OpenAI gem

readme.md

The documentation at https://github.com/openai/openai-ruby is rather poor - it doesn't mention base_url or choices at all! Further, LLMs trained so far are really bad at writing code to use it. So this gist is an attempt at correcting the record for this specific use case.

openai-openrouter-multiple-models.rb

require "openai"

client = OpenAI::Client.new(
  api_key: ENV.fetch("OPENROUTER_API_KEY"),
  base_url: "https://openrouter.ai/api/v1"
)

models = %w{
  google/gemma-2b-it
  anthropic/claude-sonnet-4
  openai/o4-mini
  openai/gpt-4.1-mini
  google/gemini-2.0-flash-001
}

models.each do |model|
  resp = client.chat.completions.create(
    model:    model,
    messages: [{ role: "user", content: "Tell me a joke" }]
  )
  puts "=== #{model} ===\n\n#{resp.choices[0].message.content}\n\n"
end

openai-openrouter.rb

require "openai"

client = OpenAI::Client.new(
  api_key: ENV.fetch("OPENROUTER_API_KEY"),
  base_url: "https://openrouter.ai/api/v1"
)

resp = client.chat.completions.create(
  model:    :"openai/gpt-4o",
  messages: [{ role: "user", content: "Tell me a joke" }]
)

puts resp.choices[0].message.content

z-as-a-class.rb

class LLM
  def initialize
    @client = OpenAI::Client.new(
      api_key: ENV.fetch("OPENROUTER_API_KEY"),
      base_url: "https://openrouter.ai/api/v1"
    )
  end
  def chat(prompt, history: [])
    messages = history.map { |h| { role: h[:role], content: h[:content] } }
    messages << { role: "user", content: prompt }
    resp = @client.chat.completions.create(
      model: "amazon/nova-micro-v1",
      messages: messages
    )
    resp.choices[0].message.content
  end
end

llm = LLM.new
puts llm.chat("What is the capital of France?")