[Feature Request]: Enhanced Custom Provider Configuration (OpenCode-style) for Global LLM Ecosystem Support

[lucasllin]

Currently, Letta Code primarily relies on interactive CLI commands or environment variables for configuration. While functional, this approach is less ideal for managing complex, multi-model setups—especially when dealing with regional providers like Volcengine Ark that require specific base URLs and multiple model endpoints.

I propose implementing a declarative configuration file (e.g., letta.config.json or .lettarcconfig) that allows users to define providers and models in a structured format, similar to the flexible provider architecture found in OpenCode.

Motivation:

As an engineer managing complex Flutter projects in a WSL environment, I prefer file-based configuration over ephemeral environment variables for several reasons:

1. Reproducibility: Configuration files can be version-controlled or backed up.
2. Clarity: It’s easier to define and visualize the relationship between a Provider (e.g., Volcengine) and its multiple models (Kimi, Doubao, DeepSeek).
3. Elegance: A single JSON file is much cleaner than a long list of export statements in a .zshrc.

Proposed Configuration Structure:

The configuration should allow defining providers as top-level entities, each hosting its own set of models and specific API constraints:

{
  "model": "volcengine/ark-code-latest",
  "providers": {
    "volcengine": {
      "adapter": "openai-compatible",
      "name": "Volcengine Ark",
      "options": {
        "baseURL": "[https://ark.cn-beijing.volces.com/api/coding/v3](https://ark.cn-beijing.volces.com/api/coding/v3)",
        "apiKey": "<YOUR_API_KEY>"
      },
      "models": {
        "ark-code-latest": {
          "context_window": 256000,
          "output_limit": 4096,
          "modalities": ["text", "image"]
        },
        "kimi-k2.6": {
          "context_window": 256000,
          "modalities": ["text", "image"]
        },
        "deepseek-v4-pro": {
          "context_window": 128000
        }
      }
    }
  }
}