Working with AI Models

One API, endless possibilities! 🌐 Connect to Claude, GPT-4, Gemini, and dozens more AI models from every major provider. Switch models with a single line of code.

The Model Registry
1. Refreshing the Registry
Exploring and Finding Models
Connecting to Custom Endpoints & Using Unlisted Models
1. Custom OpenAI API Base URL (openai_api_base)
2. Assuming Model Existence (assume_model_exists)

After reading this guide, you will know:

How RubyLLM discovers and registers models.
How to find and filter available models based on provider, type, or capabilities.
How to understand model capabilities and pricing using Model::Info.
How to use model aliases for convenience.
How to connect to custom endpoints (like Azure OpenAI or proxies) using openai_api_base.
How to use models not listed in the default registry using assume_model_exists.

The Model Registry

RubyLLM maintains an internal registry of known AI models, typically stored in lib/ruby_llm/models.json within the gem. This registry is populated by running the rake models:update task, which queries the APIs of configured providers to discover their available models and capabilities.

The registry stores crucial information about each model, including:

id: The unique identifier used by the provider (e.g., gpt-4o-2024-08-06).
provider: The source provider (openai, anthropic, etc.).
type: The model’s primary function (chat, embedding, etc.).
name: A human-friendly name.
context_window: Max input tokens (e.g., 128_000).
max_tokens: Max output tokens (e.g., 16_384).
supports_vision: If it can process images.
supports_functions: If it can use Tools.
input_price_per_million: Cost in USD per 1 million input tokens.
output_price_per_million: Cost in USD per 1 million output tokens.
family: A broader classification (e.g., gpt4o).

This registry allows RubyLLM to validate models, route requests correctly, provide capability information, and offer convenient filtering.

You can see the full list of currently registered models in the Available Models Guide.

Refreshing the Registry

For Application Developers:

The recommended way to refresh models in your application is to call RubyLLM.models.refresh! directly:

# In your application code (console, background job, etc.)
RubyLLM.models.refresh!
puts "Refreshed in-memory model list."

This refreshes the in-memory model registry and is what you want 99% of the time. This method is safe to call from Rails applications, background jobs, or any running Ruby process.

For Gem Development:

The rake models:update task is designed for gem maintainers and updates the models.json file shipped with the gem:

# Only for gem development - requires API keys and gem directory structure
bundle exec rake models:update

This task is not intended for Rails applications as it writes to gem directories and requires the full gem development environment.

Persisting Models to Your Database:

If you want to store model information in your application’s database for persistence, querying, or caching, create your own migration and sync logic. Here’s an example schema and production-ready sync job:

# db/migrate/xxx_create_llm_models.rb
create_table "llm_models", force: :cascade do |t|
  t.string "model_id", null: false
  t.string "name", null: false
  t.string "provider", null: false
  t.boolean "available", default: false
  t.boolean "is_default", default: false
  t.datetime "last_synced_at"
  t.integer "context_window"
  t.integer "max_output_tokens"
  t.jsonb "metadata", default: {}
  t.datetime "created_at", null: false
  t.datetime "updated_at", null: false
  t.string "slug"
  t.string "model_type"
  t.string "family"
  t.datetime "model_created_at"
  t.date "knowledge_cutoff"
  t.jsonb "modalities", default: {}, null: false
  t.jsonb "capabilities", default: [], null: false
  t.jsonb "pricing", default: {}, null: false

  t.index ["model_id"], unique: true
  t.index ["provider", "available", "context_window"]
  t.index ["capabilities"], using: :gin
  t.index ["modalities"], using: :gin
  t.index ["pricing"], using: :gin
end

# app/jobs/sync_llm_models_job.rb
class SyncLLMModelsJob < ApplicationJob
  queue_as :default
  retry_on StandardError, wait: 1.seconds, attempts: 5

  def perform
    RubyLLM.models.refresh!

    found_model_ids = RubyLLM.models.chat_models.filter_map do |model_data|
      attributes = model_data.to_h
      attributes[:model_id] = attributes.delete(:id)
      attributes[:model_type] = attributes.delete(:type)
      attributes[:model_created_at] = attributes.delete(:created_at)
      attributes[:last_synced_at] = Time.now

      model = LLMModel.find_or_initialize_by(model_id: attributes[:model_id])
      model.assign_attributes(**attributes)
      model.save ? model.id : nil
    end

    # Mark missing models as unavailable instead of deleting them
    LLMModel.where.not(id: found_model_ids).update_all(available: false)
  end
end

# Schedule it to run periodically
# config/schedule.rb (with whenever gem)
every 6.hours do
  runner "SyncLLMModelsJob.perform_later"
end

Exploring and Finding Models

Use RubyLLM.models to explore the registry.

Listing and Filtering

# Get a collection of all registered models
all_models = RubyLLM.models.all

# Filter by type
chat_models = RubyLLM.models.chat_models
embedding_models = RubyLLM.models.embedding_models

# Filter by provider
openai_models = RubyLLM.models.by_provider(:openai) # or 'openai'

# Filter by model family (e.g., all Claude 3 Sonnet variants)
claude3_sonnet_family = RubyLLM.models.by_family('claude3_sonnet')

# Chain filters and use Enumerable methods
openai_vision_models = RubyLLM.models.by_provider(:openai)
                                   .select(&:supports_vision?)

puts "Found #{openai_vision_models.count} OpenAI vision models."

Finding a Specific Model

Use find to get a Model::Info object containing details about a specific model.

# Find by exact ID or alias
model_info = RubyLLM.models.find('gpt-4o')

if model_info
  puts "Model: #{model_info.name}"
  puts "Provider: #{model_info.provider}"
  puts "Context Window: #{model_info.context_window} tokens"
else
  puts "Model not found."
end

# Find raises ModelNotFoundError if the ID is unknown
# RubyLLM.models.find('no-such-model-exists') # => raises ModelNotFoundError

Model Aliases

RubyLLM uses aliases (defined in lib/ruby_llm/aliases.json) for convenience, mapping common names to specific versions.

# 'claude-3-5-sonnet' might resolve to 'claude-3-5-sonnet-20241022'
chat = RubyLLM.chat(model: 'claude-3-5-sonnet')
puts chat.model.id # => "claude-3-5-sonnet-20241022" (or latest version)

find prioritizes exact ID matches before falling back to aliases.

Provider-Specific Resolution

Specify the provider if the same alias exists across multiple providers.

# Get Claude 3.5 Sonnet from Anthropic
model_anthropic = RubyLLM.models.find('claude-3-5-sonnet', :anthropic)

# Get Claude 3.5 Sonnet via AWS Bedrock
model_bedrock = RubyLLM.models.find('claude-3-5-sonnet', :bedrock)

Connecting to Custom Endpoints & Using Unlisted Models

Sometimes you need to interact with models or endpoints not covered by the standard registry, such as:

Azure OpenAI Service endpoints.
API Proxies & Gateways (LiteLLM, Fastly AI Accelerator).
Self-Hosted/Local Models (LM Studio, Ollama via OpenAI adapter).
Brand-new model releases.
Custom fine-tunes or deployments with unique names.

RubyLLM offers two mechanisms for these cases:

Custom OpenAI API Base URL (`openai_api_base`)

If you need to target an endpoint that uses the OpenAI API format but has a different URL, configure openai_api_base in RubyLLM.configure.

# config/initializers/ruby_llm.rb
RubyLLM.configure do |config|
  config.openai_api_key = ENV['AZURE_OPENAI_KEY'] # Key for your endpoint
  config.openai_api_base = "https://YOUR_AZURE_RESOURCE.openai.azure.com" # Your endpoint
end

This setting only affects requests made with provider: :openai.
It directs those requests to your specified URL instead of https://api.openai.com/v1.
See Installation Guide.

Assuming Model Existence (`assume_model_exists`)

To use a model identifier not listed in RubyLLM’s registry, use the assume_model_exists: true flag. This tells RubyLLM to bypass its validation check.

# Example: Using a custom Azure deployment name
# Assumes openai_api_base is configured for your Azure endpoint
chat = RubyLLM.chat(
  model: 'my-company-secure-gpt4o', # Your custom deployment name
  provider: :openai,                # MUST specify provider
  assume_model_exists: true         # Bypass registry check
)
response = chat.ask("Internal knowledge query...")
puts response.content

# You can also use it in .with_model
chat.with_model(
  model: 'gpt-5-alpha',
  provider: :openai,                # MUST specify provider
  assume_exists: true
)

The assume_model_exists flag also works with RubyLLM.embed and RubyLLM.paint for embedding and image generation models:

# Custom embedding model
embedding = RubyLLM.embed(
  "Test text",
  model: 'my-custom-embedder',
  provider: :openai,
  assume_model_exists: true
)

# Custom image model
image = RubyLLM.paint(
  "A beautiful landscape",
  model: 'my-custom-dalle',
  provider: :openai,
  assume_model_exists: true
)

Key Points when Assuming Existence:

provider: is Mandatory: You must tell RubyLLM which API format to use (ArgumentError otherwise).
No Validation: RubyLLM won’t check the registry for the model ID.
Capability Assumptions: Capability checks (like supports_functions?) are bypassed by assuming true. You are responsible for ensuring the model supports the features you use.
Your Responsibility: Ensure the model ID is correct for the target endpoint.
Warning Log: A warning is logged indicating validation was skipped.

Use these features when the standard registry doesn’t cover your specific model or endpoint needs. For standard models, rely on the registry for validation and capability awareness. See the Chat Guide for more on using the chat object.