Cutting insert, cutting tool, and method for manufacturing machined product

A cutting insert comprising:

• an upper surface comprising a first corner having a protruding curve shape and a first side and a second side extending from the first corner;
• a lower surface located on an opposite side to the upper surface;
• lateral surfaces located between the upper surface and the lower surface;
• a cutting edge located on the first corner and the first side;
• and
• a through hole that opens in the upper surface and the lower surface, wherein the lateral surfaces comprise:
• a first lateral surface extending from the first side to the lower surface;
• and
• a second lateral surface extending from the second side to the lower surface,
• in a front view of the upper surface, a virtual straight line passing through a front end of the first corner and extending in a major axis direction of the upper surface is referred to as an axis,
• the first lateral surface comprises:
• a first region that has a recessed shape recessed toward the axis;
• and
• a second region that is flat and is located farther from the first corner than the first region,
• the upper surface further comprises a recessed portion that is located between the second side and the axis and is recessed toward the axis in a front view of the upper surface, and
• an entirety of the recessed portion is located farther from the first corner than an entirety of the first region in a direction along the axis.