How do I force nodes to have revisions by default when using REST? We have a headless Drupal 8 content repository which we access via the REST API.  I'd like Drupal to track revisions automatically for all nodes, as soon as they are created.  I'm only aware of the "create new revision" checkbox on the node edit form.

How might I set Drupal to create revisions automatically?

All nodes are created programmatically via the REST API.
The node type setting mentioned by the other answers only applies to the node form, it does not affect programatically saved nodes.

You could try to implement hook_node_presave() and call setNewRevision(TRUE) or maybe the same in hook_node_load(). Or override the rest plugin (assuming you use that and not your own controllers).