> Thus far, causal consistency has generally been limited to research projects ... MongoDB is one of the first commercial databases we know of which provides an implementation.

Cosmos DB provides session consistency (looks like an another name for causal consistency) at least since 2014 [1].

Cosmos DB's session guarantees [2]: consistent prefix, monotonic reads, monotonic writes, read-your-writes, write-follows-reads.

Mongo DB's causal consistency guarantees [3]: monotonic reads, monotonic writes, read-your-writes, write-follows-reads.

Doubt that four years later still qualities as one of the first.

[1] https://www.infoq.com/news/2014/08/microsoft-azure-documentd...

[2] https://docs.microsoft.com/en-us/azure/cosmos-db/consistency...

[3] https://docs.mongodb.com/manual/core/read-isolation-consiste...