Current breaking changes

Hydra 1.4 and OmegaConf 2.4 are still under development. This page is a working inventory of changes currently known to require application updates. It is derived from their news fragments, may change, and may not yet be complete. The final release notes will be the authoritative list.

Hydra 1.4

• Python 3.7, 3.8, and 3.9 are no longer supported. Hydra requires Python 3.10 or newer.
• The unsupported Torchrun launcher and the contrib plugin area have been removed.
• The experimental on_compose_config callback has been removed. It was never included in a stable Hydra release, but was available in Hydra 1.4 development versions from February 2025 through July 2026.
• Parent traversal in Defaults List config paths is no longer accepted.

Hydra 1.1 compatibility behavior

version_base="1.1" is no longer accepted, and the following legacy behavior has been removed:

• Omitting config_path no longer adds the calling directory to the config search path.
• hydra.job.chdir defaults to False.
• Config files using the .yml extension are rejected; use .yaml.
• The old {group: option, optional: true} Defaults List syntax is rejected; use optional group: option.
• Defaults List entries that replace Hydra config groups require the override keyword.
• Indexed Defaults List interpolations such as ${defaults.0.dataset} are no longer accepted.
• _group_ and _name_ are no longer expanded as symbolic package values.
• The strict argument to hydra.compose() has been removed.
• ConfigStore schemas are no longer matched automatically by config name. Use explicit schema extension in the Defaults List.

Hydra 1.2 migration behavior

version_base="1.2" is no longer accepted, and the following migration paths have been removed:

• hydra.types.TargetConf has been removed. Use a Structured Config with a _target_ field.
• The hydra.experimental compose and initialization APIs have been removed. Import them from hydra.
• hydra.job.chdir=null is no longer accepted. Set it to True or False.
• Direct callers of the internal run_job() API must pass hydra_context.
• Third-party Sweepers must use the HydraContext supplied to setup() to access the config loader.
• Optuna Sweeper's deprecated hydra.sweeper.search_space configuration has been removed. Use hydra.sweeper.params.

Instantiation

• hydra.utils.instantiate() passes dataclass and attrs instances supplied as call-site arguments through unchanged instead of interpreting them as Structured Configs.
• hydra.utils.instantiate() resolves interpolations during recursive traversal instead of resolving the entire configuration before instantiation. With _recursive_=False and _convert_="none", Config containers are passed through without a final copy. See Instantiate resolution and call-site overrides.
• Launcher and sweeper plugin configurations are instantiated non-recursively.
• Some security-sensitive modules can no longer be instantiated by default. This restriction is not a security boundary; do not rely on it to make untrusted configurations safe.

OmegaConf 2.4

• Python 3.6, 3.7, 3.8, and 3.9 are no longer supported. OmegaConf requires Python 3.10 or newer.
• Native tuples create immutable TupleConfig values instead of mutable ListConfig values, and conversion returns tuples instead of lists. See the OmegaConf tuple migration guide.
• OmegaConf.create(None) returns None instead of a DictConfig wrapping None.
• OmegaConf.get_type() returns NoneType for nodes containing None, and None and NoneType annotations are validated.
• OmegaConf.resolve() raises InterpolationToMissingValueError when an interpolation dereferences a missing (???) value instead of replacing the node with ???.
• OmegaConf.to_container(..., resolve=True) resolves a custom resolver at most once per resolved node during a conversion pass. Code relying on repeated side effects from the same resolver may behave differently.
• A backslash immediately before a key-path delimiter now escapes that delimiter. This changes the interpretation of key paths involving keys whose names end in a backslash.