List all available models for a provider

[stefanorosanelli]

Checked

• I searched existing ideas and did not find a similar one
• I added a very descriptive title
• I've clearly described the feature request and motivation for it

Feature request

It would be nice to have a standard way in LangChain to get the list of available models for a given provider.
All the major LLM provider APIs provide such support and it would be nice to have a standard interface to get this information.
Currently this possibility is not available in LangChain.

Some examples for the main vendors:

• OpenAI Models endpoint
• Cohere List Models
• Ollama List Local Models
• Anthropic List Models

Motivation

A typical use case for this feature request is to show a user the models available for a certain provider and to be able to select them for the LLM application they are using.
Applications could provide a list that is always updated in real time without having to manage ad hoc configurations.

Proposal (If applicable)

A possible solution could be to add a method in BaseChatModel, for example list_models(), to show the list of available models.
The available information should be made uniform since each provider provides different attributes. But at least the name is always present.
To be investigated whether to extend support to other types of models via BaseLLM or Embeddings