Function Runtime Versioning

The Functions runtime runs as a site extension in your Function App. In your app settings, you'll find a version specifier FUNCTIONS_EXTENSION_VERSION which is set to a major version specifier, e.g.:

That value ~0.4 indicates that your Function App will stay on the 0.4 major version train. It won't be moved forward to any new major versions (which contain breaking changes). You will however be moved forward to new minor versions containing bug fixes, new features, etc. This allows you to manage when you take breaking changes. For release notes (including breaking changes) for each release, see here.

When we deploy a new major version, the Functions Portal will give you the option to move yourself forward:

All this update button does is set the FUNCTIONS_EXTENSION_VERSION app setting to a new value (the next major version specifier).