1.18.0

Released: January 9, 2026

feature

• [feature] [operations] When alembic is run in "verbose" mode, alembic now logs a message to
  indicate from which file is used to load the configuration.

  References: #1737

• [feature] [autogenerate] Autogenerate reflection sweeps now use the "bulk" inspector methods
  introduced in SQLAlchemy 2.0, which for selected dialects including
  PostgreSQL and Oracle use batched queries to reflect whole collections of
  tables using O(1) queries rather than O(N).

  References: #1771

• [feature] [autogenerate] Release 1.18.0 introduces a plugin system that allows for automatic
  loading of third-party extensions as well as configurable autogenerate
  compare functionality on a per-environment basis.

  The Plugin class provides a common interface for extensions that
  register handlers among Alembic's existing extension points such as
  Operations.register_operation() and
  Operations.implementation_for(). A new interface for registering
  autogenerate comparison handlers,
  Plugin.add_autogenerate_comparator(), provides for autogenerate
  compare functionality that may be custom-configured on a per-environment
  basis using the new
  EnvironmentContext.configure.autogenerate_plugins parameter.

  The change does not impact well known Alembic add-ons such as
  alembic-utils, which continue to work as before; however, such add-ons
  have the option to provide plugin entrypoints going forward.

  As part of this change, Alembic's autogenerate compare functionality is
  reorganized into a series of internal plugins under the
  alembic.autogenerate namespace, which may be individually or
  collectively identified for inclusion and/or exclusion within the
  EnvironmentContext.configure() call using a new parameter
  EnvironmentContext.configure.autogenerate_plugins. This
  parameter is also where third party comparison plugins may also be
  indicated.

  See alembic.plugins.toplevel for complete documentation on
  the new Plugin class as well as autogenerate-specific usage
  instructions.

usecase

• [usecase] [environment] The file_template configuration option now supports directory paths,
  allowing migration files to be organized into subdirectories. When using
  directory separators in file_template (e.g.,
  %(year)d/%(month).2d/%(day).2d_%(rev)s_%(slug)s), Alembic will
  automatically create the necessary directory structure. The
  recursive_version_locations setting must be set to true when using
  this feature in order for the revision files to be located for subsequent
  commands.

  References: #1774

• [usecase] Avoid deprecation warning in add/drop constraint added in SQLAlchemy 2.1.
  Ensure that alembic is compatible with the changes added in
  sqlalchemy/sqlalchemy#13006
  by explicitly setting isolate_from_table=True when running with
  SQLAlchemy 2.1 or greater.

bug

• [bug] [postgresql] Fixed issue where PostgreSQL sequence defaults on non-primary key columns
  were incorrectly detected as changed on every autogenerate run. Server
  default comparison logic is adjusted to filter out the ::regclass
  expression added by the server which interferes with the comparison.

  References: #1507

• [bug] [mssql] Implemented DDL for column comment add/update/delete when using the
  Operations.alter_column.comment parameter with
  Operations.alter_column() on Microsoft SQL Server. Previously,
  these functions were not implemented for SQL Server and would raise
  UnsupportedCompilationError.

  References: #1755