FaunaDB 2.5.4

Furthermore, read-only transactions, for performance reasons, also execute at snapshot isolation, and may return stale data:

After careful consultation with Fauna’s engineers, we believe FaunaDB’s intended consistency levels fall between snapshot isolation and strict serializability, depending on whether the transaction is read-only, whether indices are used, and whether those indices are flagged as serializable. We designed a family of workloads for FaunaDB using the Jepsen library, designed to stress inserts, single-key linearizable transactions, multi-key snapshot isolation, pagination, phantoms, monotonicity, temporal queries, and internal consistency within transactions. Because FaunaDB treats read-only and update transactions differently, a variant of the set test uses a “strong read” transaction, which includes a spurious write to an unrelated class in order to force the transaction to go through the full commit path.

Source: jepsen.io