After maintenance begins, we will cancel all open orders. When the site is back online, markets will be in post-only mode for a short time before we reopen trading. Your funds will be safe during maintenance, and you do not need to do anything at this time. For more details, please see our FAQs. For updates on the upgrade while it’s underway, please check our Twitter account.
We appreciate your patience as we work to improve your Poloniex experience. This upgrade lays the groundwork for developing new features and reviving some old, beloved functionality. We’re excited for what’s next!
As always, if you have any questions, please reach out to our support team here.
Best,
The Poloniex Team
https://poloniex.freshdesk.com/support/solutions/articles/1000271998-faq-for-planned-maintenance-on-december-17-2018-