Do you need a CDL to driver a 26000 lb truck?

If you mean a vehicle with a Gross Vehicle Weight Rating in excess of 26,000 lbs, typically, yes, although there are some exceptions:

• Recreational vehicles, when not operated or driven on a for-hire basis.
• First response emergency vehicles, although states or departments can require a CDL if they see fit to
• Farm vehicles, provided that they are registered as farm vehicles, are used only for the activities of that farm, are operated within a 150 mile radius of that farm, and are operated by the farmer, family members of the farmer, or direct (W2) employees of that farmer.
• Military vehicles, provided that they are operated by military personnel in the course of their duties.

A vehicle under 26,000 lbs. GVW only requires a CDL if it is either a vehicle carrying a quantity of hazmat which requires placards to be displayed, a bus transporting more than 15 persons (including the driver), or, when combined with a trailer, is part of a combination with a Gross Combined Weight Rating in excess of 26,000 lbs., if it doesn't fall under any of the above listed exemptions for vehicles with a GVW in excess of 26,000 lbs.