That is an excellent compare & contrast. The both use 64 bit IDs.
Instagram: 13 bit shard ID, 51 bit "local" ID consisting of 41 bit timestamp in milliseconds and 10 bit sub-millisecond ID. So this scheme supports 1024 IDs per millisecond per shard for 41 years, and 8192 shards.
Pinterest: 16 bit shard ID, 10 bit type ID(?), 36 bit local ID, 2 bits reserved. This supports 68 billion objects per shard and 65K shards, but does not represent time. So you need another field / more storage for that. Also notable is the large 10 bit type ID field which seems to be only actually used for a handful of values, leading to a large chunk of bits that don't change across IDs.
In short, Instagram's scheme is more efficient largely due to the leverage of timestamps in the ID instead of type information.
Instagram: 13 bit shard ID, 51 bit "local" ID consisting of 41 bit timestamp in milliseconds and 10 bit sub-millisecond ID. So this scheme supports 1024 IDs per millisecond per shard for 41 years, and 8192 shards.
Pinterest: 16 bit shard ID, 10 bit type ID(?), 36 bit local ID, 2 bits reserved. This supports 68 billion objects per shard and 65K shards, but does not represent time. So you need another field / more storage for that. Also notable is the large 10 bit type ID field which seems to be only actually used for a handful of values, leading to a large chunk of bits that don't change across IDs.
In short, Instagram's scheme is more efficient largely due to the leverage of timestamps in the ID instead of type information.