Telemetry is a clean sounding euphemism for tracking.

Gatsby gives you a notice when you first start it:

Gatsby collects anonymous usage analytics to help improve Gatsby for all users.

In your ~/.config directory, Gatsby has created some files related to telemetry:

gatsby/
├── config.json
├── events.json
└── sites/
    └── 1932d81eba27c5c367844801f29aa32e/
        ├── developproxy.json
        ├── developstatusserver.json
        ├── metadata.json
        ├── recipesgraphqlserver.json
        └── telemetryserver.json

If you look into the config.json, you can see that tracking is enabled by default:

{
  "telemetry": {
    "machineId": "72a8ea824-93ee-568a-f458-2bdab942a597",
    "enabled": true
  },
  "feedback": {
    "firstCheckDate": 1608330787473
  }
}

Like the note said, it can be turned off:

$ gatsby telemetry --disable

If you don’t have Gatsby installed globally, call the local Gatsby binary from the .bin:

$ node_modules/.bin/gatsby telemetry --disable

You can also define an environment variable in your .env file or elsewhere:

GATSBY_TELEMETRY_DISABLED=1

You can read more about how and why they track you, and the telemetry related code is also open source, like the rest of Gatsby.