Using Downsizing with Zed

Prerequisites

Install the Downsizing CLI — see the CLI guide if you haven't already.

Link Zed (Recommended)

Link Zed to Downsizing:

ds link zed

This writes a custom provider entry into ~/.config/zed/settings.json, under language_models.anthropic_compatible.Downsizing— Zed's documented mechanism for custom Anthropic-protocol endpoints, using the native Anthropic Messages API rather than the OpenAI Chat Completions API. It's idempotent — safe to run again any time, and only ever touches the single entry it owns, leaving the rest of your settings file (theme, keybindings, other providers) untouched.

Zed doesn't allow API keys inside settings.json — normally a custom provider's key must come from an environment variable or the system keychain. Downsizing routes around that by sending your routing secret via Zed's custom_headerssupport instead, so there's no extra environment variable or keychain step to configure.

Select the model

Open Zed's Agent Panel, click the model picker, and choose Downsizingunder "Anthropic Compatible".

Manual Setup

If you prefer to configure manually, open Zed's settings (zed: open settings) and add:

{
  "language_models": {
    "anthropic_compatible": {
      "Downsizing": {
        "api_url": "https://api.downsizing.dev/YOUR_INFERENCE_ID/anthropic",
        "custom_headers": {
          "X-Downsizing-Secret": "dws_YOUR_API_KEY"
        },
        "available_models": [
          {
            "name": "claude-opus-4-8",
            "display_name": "Downsizing",
            "max_tokens": 200000,
            "max_output_tokens": 32000,
            "capabilities": {
              "tools": true,
              "images": true,
              "prompt_caching": true
            }
          }
        ]
      }
    }
  }
}

Find your Inference ID and API key on the Inference API page.

Verify

Open the Agent Panel, select the Downsizing model, and send a message. If Zed responds, Downsizing is set up correctly. You can also check your savings dashboard to see the request appear in your usage metrics.

Unlinking

To remove Downsizing from Zed:

ds unlink zed