Kraken Exchange is well-known as a US based prominent Bitcoin exchange operating in Canada, the EU, Japan, and the US, and “the world’s largest Bitcoin exchange in euro volume and liquidity”.
Initially, Kraken stated that a system upgrade would be performed on January 6 at approximately 22:00 UTC (2 pm PT).
Kraken services will be offline for about 2 hours during the upgrade, possibly longer. Withdrawals in all currencies will be offline for an additional 2-3 hours after other systems come online. If you submit a withdrawal request while withdrawals are offline, the withdrawal will be sent after withdrawals come online again.
Kraken Exchange Status
Later, the messages started to appear on the Kraken Status page claiming that the upgrade would be delayed for a few more hours.
Kraken Status towards system upgrade
On January 7 at 9 o'clock UTC Kraken Exchange reported that the upgrade is still being delayed due to the technical issues, and is currently presumably scheduled for Jan 7, 20:00 - 22:00 UTC.