After a stint in Beta, Patch IV has now been officially released to the wider public. If you are not attached to your current campaigns then it has been recommended that players start a new campaign to enjoy the full benefits of the update. However, old campaigns should still work fine, mods excluded, regardless.
Patch IV reportedly includes over 175 changes, and if you are curious to read through the full changelog it is available
here. Whilst a Patch V Beta will apparently be available some time next week, featuring further performance and gameplay improvements.