New model routing gateways might use a gateway.dev default hostname

## Change Change **New model routing gateways might use a gateway.dev default hostname** If you create a gateway that uses model routing on or after September 3, 2026, it might receive a `gateway.dev` default hostname instead of a `run.app` one, in the form `https://GATEWAY_ID-PROJECT_NUMBER.REGION.gateway.dev` — for example, `https://my-gateway-123456789012.us-central1.gateway.dev`. This is a second `gateway.dev` format; other gateways keep the existing one. To get a gateway's URL, read its `defaultHostname` property. For more information, see [Deploy an API to a gateway](https://cloud.google.com/api-gateway/docs/deploying-api).