Hello @lex. Welcome to the Coinbase Cloud Developer Forum! I understand that you would like to obtain open orders via the REST API. I also appreciate your request to have an order_id for both open and cancelled orders.
I believe you may utilize the List orders endpoint of Advanced Trade API to be able to get a list of orders. You may opt to filter the responses according to the order_status which are pending, filled, cancelled, expired, failed, and unknown_order_status. Also, you may utilize the Cancel orders endpoint if you want to initiate cancel requests for one or more orders. You will be given an order_id for every order that you initiate. You may check this documentation link for the available Advanced Trade endpoints: REST API Overview
In reference to this forum thread, it seems that the only way to get all the active orders is to call your entire order history and parse it yourself, but this will be unfeasible in the future if you’ve made several orders in your account. On that note, @bredy has a workaround with regard to this matter. You may try that as well. I highly appreciate your help here, @bredy.
Having that said, I recommend that you post any feedback or feature requests that you have in the Feedback Section of the Developer Forum as most new features and improvements to Coinbase come directly from feedback like yours. Additionally, you may engage in the Advanced Trade Feedback thread as I would love to know what you think about the newly launched Advanced Trade API. Thank you!