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While the interface cost is limited to 65,535 because of LSA field limitations, the path metric can exceed a 16-bit value (65,535) because all the link metrics are calculated locally.

From

Cover of IP Routing on Cisco IOS, IOS XE, and IOS XR: An Essential Guide to Understanding and Implementing IP Routing Protocols

Note

Cost that exceed this limitation may be constraint or experience issues when the route to the node is exchanged between peers.