Previously, altering a column’s type requiring a backfill required the enable_experimental_alter_column_type_general setting to be enabled. This restriction has been removed, as full support for ALTER COLUMN TYPE has been implemented in the Declarative Schema Changer (DSC).
The setting is still checked in mixed-version clusters, as the operation relies on 25.1 dependency rules, and when using the legacy schema changer.
Epic: CRDB-25314
Informs #49329
Release note (general): Altering a column’s type no longer requires enabling the enable_experimental_alter_column_type_general setting. This change makes the feature generally available.
cockroach-teamcity
commented
14 hours ago 
Previously, altering a column’s type requiring a backfill required the enable_experimental_alter_column_type_general setting to be enabled. This restriction has been removed, as full support for ALTER COLUMN TYPE has been implemented in the Declarative Schema Changer (DSC).
The setting is still checked in mixed-version clusters, as the operation relies on 25.1 dependency rules, and when using the legacy schema changer.
Epic: CRDB-25314 Informs #49329 Release note (general): Altering a column’s type no longer requires enabling the enable_experimental_alter_column_type_general setting. This change makes the feature generally available.