Why won't my tracked array update in Ember Octane?

I'm trying out Octane, and for some reason, if I show an array in a template and I add a new object to it, the UI doesn't update. What am I doing wrong?

Here is my template:

<label for="new-field-name">Field Name</label>
<Input id="new-field-name" @value= type="text" />
<button >Add field</button>


    <p></p>

And the component:

import Component from '@glimmer/component';
import { tracked } from '@glimmer/tracking';
import { action } from '@ember/object';

export default class ConfigControlsComponent extends Component {
    @tracked fields = []
    @tracked newFieldName = ''

    @action addField() {
        this.fields.push({
            name: this.newFieldName
        })
        console.log(this.fields)
    }
}

The console.log shows the array with the new object added to it, and the fields array is tracked, but nothing changes when I click the button.