We updated the babel-preset-kyt-core and babel-preset-kyt-react presets with babel-preset-env. Before 0.9, kyt automatically included babel-polyfill into your bundle. With the recent changes, you'll have to manually install babel-polyfill into your package.json dependencies (not devDependencies), and import 'babel-polyfill;' at the top of your src/client/index.js and src/server/index.js file. This will optimize your server build by targeting the current version of Node and by targeting a limited set of browsers using a browserslist configuration on the client build. You can read more about extending the babel-preset-env settings via the envOptions in babel-preset-kyt-core.
In 0.9, we added better support for static assets, including new rules and fingerprinting. You'll find more documentation in the conventions doc.
A new rule in eslint-config-kyt is configured to restrict server file imports from outside of the src/server directory. The change you'll need to make in your project is to add this .eslintrc.js to your src/server directory. The current starter-kyt version includes this configuration.