Instruments and related methods for breaking reduction tabs are disclosed herein, e.g., for breaking reduction tabs of a bone anchor or other implant. In some embodiments, the instrument can be configured to minimize the space needed to operate the instrument. For example, the instrument can be configured to receive a reduction tab that is to be broken while the instrument is coaxially positioned with respect to a bone anchor receiver to which the reduction tab is attached. As another example, the instrument can have a maximum outer transverse dimension that is less than, equal to, or only slightly greater than a corresponding dimension of a bone anchor from which a reduction tab is to be broken. Guide rods for positioning a tab breaker instrument over a reduction tab are also disclosed.