Limited set of queries impacted by Cypher 25 issue

What Happened

Neo4j commenced the deployment of version 2026.01.1 to Aura free instances at 07:49 AM UTC on January 26, 2026. Following the detection of query failures during internal testing, the rollout was halted before it reached Aura higher tiers. 

The failures occurred on conditional queries (e.g. WHEN …THEN …) after the planner phase to behave differently in the case of aggregation over null values.

We identified the root cause and developed a resolution, which was integrated into version 2026.01.2. On January 27, 2026, we began deploying 2026.01.2 across Aura instances, successfully upgrading all affected environments to the corrected version

How the service was affected

Queries using WHEN in 2026.01.1 in combination with aggregation over null values get an incorrect number of rows returned. Queries using NEXT can in some instances produce an unexpected variable not defined error. This caused the rewritten query to behave differently in the case of aggregation over null values. 

The conditional query would need to receive incoming rows containing null values and be aggregating over the values without using a grouping. Customers received an incorrect result if they were using the conditional query construct in Cypher 25 (see https://neo4j.com/docs/aura/managing-instances/cypher-version/), an impact that was limited to a limited number of Aura instances. 

What are we doing now

We have enhanced our testing procedures to ensure comprehensive coverage across all product areas. This includes the development of new test cases designed to address both identified issues and potential future scenarios. 

Furthermore, we have integrated Cypher query testing within Aura as a standard component of our regression testing suite. These checks are now mandatory stages within our Continuous Integration pipeline and staging environments prior to any production rollout.