Scalloped mateface seal arrangement for CMC platforms

A flow path component assembly, comprising:

• a flow path component having a plurality of segments extending circumferentially about an axis to bound a core flow path;
• at least one of the segments having a platform extending circumferentially between a first side and a second side, a slot in the first side, the slot extending circumferentially and axially to divide the platform into a first portion and a second portion, and a groove along the first side in the first portion, wherein the groove is a semicircle, wherein the second portion includes a hot side surface bounding the core flow path, the first portion includes a cold side surface on an opposite side of the platform, wherein the groove is circumferentially and axially aligned with, but is spaced apart from, the second portion of the platform, and wherein the semicircle groove is one of a plurality of grooves spaced axially along the first side in the first portion;
• and
• wherein the groove extends circumferentially inward from the first side to establish a first width, the slot extends circumferentially inward from the first side to establish a second width, and the second width is greater than the first width such that the slot extends circumferentially past the groove relative to the axis.