---
sidebar_position: 2
description: |-
  From OpenTofu v1.6 onwards the OpenTofu team promises to preserve backward
  compatibility for most of the OpenTofu language and the primary CLI
  workflow, until the next major release.
---

# OpenTofu v1.x Compatibility Promises

The release of OpenTofu v1.6 represents an important milestone in the
development of the OpenTofu language and workflow. OpenTofu v1.x is a stable
platform for describing and managing infrastructure.

In this release we're defining a number of OpenTofu behaviors that we intend
to remain compatible with throughout the 1.x releases:

* A large subset of OpenTofu language features.
* A more conservative subset of the OpenTofu CLI workflow commands.
* The wire protocol for communication between OpenTofu Core and OpenTofu
  providers.
* The wire protocols for installation of providers and external modules.

Our intention is that modules written for OpenTofu v1.6 will
continue to plan and apply successfully, without required changes, throughout
the v1.x releases.

We also intend that automation built around the workflow subset described in
this document will work without changes in all future v1.x releases.

Finally, we intend that providers built against the currently-documented
provider wire protocol will be compatible with all future OpenTofu v1.x
releases targeting the same operating system and architecture, without the
need for source code modification or binary recompilation.

In short, we aim to make upgrades between v1.x releases straightforward,
requiring no changes to your configuration, no extra commands to run upgrade
steps, and no changes to any automation you've set up around OpenTofu.

The OpenTofu v1.x series will be actively maintained for at least 18 months
after v1.6.

The following sections include some specific guidance on what we will promise
throughout the v1.x series, for those who would like full details. At
a higher level though, we don't intend to make any changes that would cause
existing modules or automation to require changes when upgrading to a new
v1.x release. We will generally treat compatibility problems in new OpenTofu
CLI releases as bugs to be fixed unless there was a very significant
justification for the change, such as in addressing a critical security
problem or matching with a breaking change to a remote dependency that isn't
directly under our control.

## The OpenTofu Language

The main OpenTofu Language includes the language syntax, the top-level
structures such as `resource`, `module`, and `provider` blocks, the
"meta-arguments" in those blocks, and the documented semantics and behaviors
for the operators and built-in functions available for use in expressions.

There is not a single formal specification for the OpenTofu language, but the
Configuration section of the documentation on the OpenTofu website serves as a
description of the language features and their intended behaviors.

The following top-level blocks and their defined "meta-arguments" (that is,
arguments defined by OpenTofu Core rather than by external plugins such as
providers) will retain their current functionality:

* [`resource`](resources/index.mdx) and
  [`data`](data-sources/index.mdx) blocks to
  declare resources, including their nested block types `lifecycle`,
  `connection`, and `provisioner`, and their meta-argument `provider`.
* [`module`](modules/syntax.mdx) blocks to call other modules,
  and its meta-argument `providers`.
* The [`count`](meta-arguments/count.mdx),
  [`for_each`](meta-arguments/for_each.mdx), and
  [`depends_on`](meta-arguments/depends_on.mdx) meta-arguments
  in `resource`, `data`, and `module` blocks.
* [`provider`](providers/configuration.mdx) blocks to configure
  providers, and the `alias` meta-argument.
* [`variable`](values/variables.mdx#declaring-an-input-variable),
  [`output`](values/outputs.mdx#declaring-an-output-value), and
  [`locals`](values/locals.mdx#declaring-a-local-value) blocks
  for declaring the various kinds of named values in a module.
* [`terraform`](settings/index.mdx) blocks, including the nested
  [`required_version`](settings/index.mdx#specifying-a-required-tofu-version)
  and
  [`required_providers`](providers/requirements.mdx#requiring-providers)
  arguments, and nested
  [`backend`](settings/backends/configuration.mdx#using-a-backend-block)
  blocks for backend configuration.

We also intend to keep compatibility with all
[expression operators](expressions/index.mdx) and
[built-in functions](functions/index.mdx), with the exception of
references to
[`terraform.workspace`](expressions/references.mdx#terraform-workspace),
whose behavior may change as part of future changes to the workspace model.

We intend to retain broad compatibility with OpenTofu language features, with
a few specific caveats:

* We consider a configuration to be valid if OpenTofu can create and apply
  a plan for it without reporting any errors.

  A configuration that currently produces errors might generate different
  errors or exhibit other non-error behaviors in a future version of
  OpenTofu. A configuration that generates errors during the apply phase
  might generate similar errors at an earlier phase in future, because
  we generally consider it better to detect errors in as early a phase as
  possible.

  Generally-speaking, the compatibility promises described in this document
  apply only to valid configurations. Handling of invalid configurations is
  always subject to change in future OpenTofu releases.
* If the actual behavior of a feature differs from what we explicitly
  documented as the feature's behavior, we will usually treat that as a bug
  and change the feature to match the documentation, although we will avoid
  making such changes if they seem likely to cause broad compatibility problems.
  We cannot promise to always remain "bug-compatible" with previous releases,
  but we will consider such fixes carefully to minimize their impact.
* Any experimental features may change or may be removed entirely from future
  releases. OpenTofu always produces a warning when an experimental language
  feature is active, to make you aware of that risk. We don't recommend using
  experimental features in production modules.
* We will introduce new language features, and if you start using them then
  your configuration won't work with prior OpenTofu versions that didn't
  support those features yet.
* Providers are separate plugins which can change independently of
  OpenTofu Core and are therefore not subject to these compatibility promises.
  If you upgrade any of the providers you are using then you might need to
  change provider or resource configurations related to those providers.
* A small number of features remain deprecated with explicit warnings in
  OpenTofu v1.6. Those deprecation cycles will end in a future v1.x release,
  at which point we will remove the corresponding features.

## Workflow

There is a set of often used OpenTofu workflows, which we are calling
_protected workflows_. We will not remove these commands, subcommands, and
flags or make backward-incompatible changes to protected workflow
functionality. If we accidentally change these, we will consider
backwards-incompatible changes to core workflows as bugs to be fixed. For a
list of the command and option combinations that are part of protected
workflows, see [Protected Workflow Commands](#protected-workflow-commands).
There is another set of commands that we are explicitly _not_ making
compatibility promises about, because we expect their functionality to change
in v1.x releases: see [Commands That Might Change](#commands-that-might-change).

The supported ways for external software to interact with OpenTofu are via
the JSON output modes offered by some commands and via exit status codes.
We may extend certain JSON formats with new object properties but we will not
remove or make breaking changes to the definitions of existing properties.

Natural language command output or log output is not a stable interface and
may change in any new version. If you write software that parses this output
then it may need to be updated when you upgrade OpenTofu. If you need access
to data that is not currently available via one of the machine-readable JSON
interfaces, we suggest opening a feature request to discuss your use-case.

## Upgrading and Downgrading

Throughout the v1.x series of releases, we intend that you should be able to
switch to a newer OpenTofu version and use it just as before, without any
special upgrade steps.

You should be able to upgrade from any v1.x release to any later v1.x release.
You might also be able to downgrade to an earlier v1.x release, but that isn't
guaranteed: later releases may introduce new features that earlier versions
cannot understand, including new storage formats for OpenTofu state snapshots.

If you make use of features introduced in a later v1.x release, your
configuration won't be compatible with releases that predate that feature.
For example, if a language feature is added in v1.7 and you start using it, your
OpenTofu configuration will no longer be compatible with OpenTofu v1.6.

## Providers

OpenTofu providers are separate plugins which communicate with OpenTofu using
a documented protocol. Therefore these compatibility promises can only cover
the "client" side of this protocol as implemented by OpenTofu Core; the
behaviors of individual providers, including which resource types they support
and which arguments they expect, are decided by the provider development teams
and can change independently of OpenTofu Core releases.

If you upgrade to a new version of a provider then you might need to change
the parts of your configuration which are interpreted by that provider, even
if you are still using an OpenTofu v1.x release.

### Provider Installation Methods

OpenTofu normally installs providers from a provider registry implementing
[the Provider Registry Protocol](../internals/provider-registry-protocol.mdx),
version 1. All OpenTofu v1.x releases will remain compatible with that
protocol, and so correctly-implemented provider registries will stay compatible.

OpenTofu also supports installation of providers from
[local filesystem directories](../cli/config/config-file.mdx#filesystem_mirror)
(filesystem mirrors) and from
[network mirrors](../cli/config/config-file.mdx#network_mirror)
(implementing [the Provider Mirror Protocol](../internals/provider-network-mirror-protocol.mdx).
All OpenTofu v1.x releases will remain compatible with those installation
methods, including
[the Implied Local Mirror Directories](../cli/config/config-file.mdx#implied-local-mirror-directories).

Specific provider registries or network mirrors are run independently from
OpenTofu itself and so their own behaviors are not subject to these
compatibility promises.

### Provider Protocol Versions

The current major version of the provider plugin protocol as of OpenTofu v1.6
is version 5, which is defined by a combination of a Protocol Buffers schema
describing the physical wire formats and by additional prose documentation
describing the expected provider behaviors.

We will support protocol version 5 throughout the OpenTofu v1.x releases. If
we make new minor revisions to protocol version 5 in later releases then we
will design them such that existing plugins will continue to work, as long as
they correctly implemented the protocol.

We may introduce new major versions of the protocol during the v1.x series. If
so, we will continue to support protocol version 5 alongside those new versions.
Individual provider teams might decide to remove support for protocol version 5
in later releases, in which case those new provider releases will not be
compatible with all of the OpenTofu v1.x releases.

## External Modules

Modules are reusable infrastructure components written in the
OpenTofu language. Some modules are "external" in the sense that OpenTofu
automatically installs them from a location other than the current
configuration directory, in which case their contents could change
independently of changes to your local modules, of the providers you use,
and of OpenTofu itself.

### Module Installation Methods

OpenTofu supports installing child modules from a number of different
[module source types](modules/sources.mdx). We will continue
to support all of the existing source types throughout the v1.x releases.

One of the supported source types is a module registry implementing
[the Module Registry Protocol](../internals/module-registry-protocol.mdx)
version 1. All OpenTofu v1.x releases will remain compatible with correct
implementations of that protocol.

Some module source types work directly with services or protocols defined and
run by third parties. Although we will not remove OpenTofu's own client-side
support for those, we cannot guarantee that their owners will keep those
services running or that they will remain compatible with OpenTofu's client
implementations.

### External Module Compatibility

If your configuration depends on external modules, newer versions of those
modules may include breaking changes. External modules are not part of
OpenTofu and are therefore not subject to these compatibility promises.

## Provisioners

We will maintain compatibility for the `file`, `local-exec`, and `remote-exec`
provisioner types through all v1.x releases.

OpenTofu supports loading additional provisioners as plugins from certain
local filesystem directories. We'll continue to support that throughout the
OpenTofu v1.x releases, but since such plugins are separate from OpenTofu
Core itself their own behaviors cannot be subject to these compatibility
promises. However, we will continue to support the plugin wire protocol as
defined in OpenTofu v1.6 throughout the v1.x releases, and so
correctly-implemented provisioner plugins should remain compatible with future
OpenTofu releases.

## State Storage Backends

When you use _remote state_, OpenTofu interacts with remote services over
the network in order to store and manage locks for OpenTofu state.

For historical reasons, all supported state storage backends are included as
part of OpenTofu CLI but not all are supported directly by the OpenTofu
Team. Only the following backends maintained by the OpenTofu team are subject
to compatibility promises:

* `local` (the default, when you are not using remote state)
* `http`

The other state storage backends are maintained by external teams via
contributions to the OpenTofu CLI codebase, and so their expected
configuration arguments or behaviors might change even in v1.x releases,
although we will aim to still ensure a good migration path in such cases,
where possible.

We are considering allowing external state storage backend implementations
via plugins, similar to provider plugins. If we introduce such a mechanism
during the v1.x releases then you may need to make configuration changes in
order to use those plugins, and state storage backends other than those
listed above may be removed from later versions of OpenTofu CLI once
equivalent plugins are available.

### The `remote` Backend

The `remote` backend's behavior may change along the way and is therefore not subject to these
compatibility promises.

## Community-maintained State Storage Backends

The `azurerm`, `consul`, `s3`, and `kubernetes` backends are maintained by
other teams at HashiCorp. Those teams intend to continue basic maintenance at
the level of bug fixes through the v1.x releases, unless we implement a plugin
protocol for backends at which point development of these backends is likely
to continue in the external plugins only, which may require configuration
changes to switch to the plugin equivalents.

The `cos`, `oss`, `pg`, `gcs`, and `etcdv3` backends are maintained by outside
contributors and are not subject to these compatibility promises.

### Unmaintained State Storage Backends

The `artifactory`, `etcdv2`, `manta`, and `swift` state storage backends do not
currently have any maintainers and thus remain in OpenTofu CLI releases on
a best-effort basis. They may be removed in later v1.x releases, and will not
be updated in case of any breaking changes to the services they integrate with.

## Supported Platforms

Throughout the v1.x series we will continue to produce official releases for
the following platforms, and make changes as necessary to support new
releases of these operating systems:

* macOS on x64 CPUs (`darwin_amd64`)
* Windows on x64 CPUs (`windows_amd64`)
* Linux on x64, 32-bit ARMv6, and 64-bit ARMv8 (`linux_amd64`, `linux_arm`, and `linux_arm64` respectively)

Over time we may require newer versions of these operating systems. For
example, subsequent OpenTofu releases in the v1.x series might end support
for earlier versions of macOS or Windows, or earlier Linux kernel releases.

We have historically produced official releases for a number of other platforms
as a convenience to users of those platforms, and we have no current plans to
stop publishing them but we cannot promise ongoing releases or bug fixes for
the other platforms throughout the v1.x series. We do not routinely test
OpenTofu on any platforms other than those listed above.

We might add support for new platforms in later v1.x releases. If so, earlier
OpenTofu releases prior to that support will not be available on those
platforms.

All OpenTofu plugins, including provider plugins, are separate programs that
have their own policies for which platforms they support. We cannot guarantee
that all providers currently support or will continue to support the platforms
listed above, even though OpenTofu CLI itself will support them.

## Later Revisions to These Promises

We may extend or refine these promises throughout the v1.x series in order to
describe promises related to new features or to clarify existing promises if
we find via feedback that our earlier statements had been unclear.

Promises for new features will be additive in the sense that they will add
further promises without retracting any existing ones. For promises that only
apply to later v1.x releases we will mention the earliest version(s) those
promises apply to.

Even if we don't add an explicit statement to this document, we intend that
any non-experimental features added in later v1.x releases will remain
compatible at least through the remainder of the v1.x series, unless otherwise
stated.

## Appendices

### Protected Workflow Commands

The following is the list of OpenTofu CLI subcommands and options that are
subject to these compatibility promises. If you build automation around
these commands then it should be compatible with all later v1.x releases.

As noted above, compatibility with external software is limited to
explicitly-machine-readable output (`-json` and `-raw` modes) and exit codes.
Any natural-language output from these commands might change in later releases.

* [`init`](../cli/commands/init.mdx)
  * `-backend=false`
  * `-backend-config=FILE`
  * `-backend-config="KEY=VALUE"`
  * `-force-copy`
  * `-get=false`
  * `-input=false`
  * `-migrate-state`
  * `-no-color`
  * `-plugin-dir=DIR`
  * `-reconfigure`
  * `-upgrade`
* [`validate`](../cli/commands/validate.mdx)
  * `-json`
  * `-no-color`
* [`plan`](../cli/commands/plan.mdx)
  * `-compact-warnings`
  * `-destroy`
  * `-detailed-exitcode`
  * `-lock=false`
  * `-lock-timeout=DURATION`
  * `-input=false`
  * `-json`
  * `-no-color`
  * `-out=FILE`
  * `-parallelism=N`
  * `-refresh=false`
  * `-refresh-only`
  * `-replace=ADDRESS`
  * `-target=ADDRESS`
  * `-var 'NAME=VALUE'`
  * `-var-file=FILE`
* [`apply`](../cli/commands/apply.mdx)
  * `-auto-approve`
  * `-compact-warnings`
  * `-lock=false`
  * `-lock-timeout=DURATION`
  * `-input=false`
  * `-json`
  * `-no-color`
  * `-parallelism=N`
  * `-refresh=false`
  * `-refresh-only`
  * `-replace=ADDRESS`
  * `-target=ADDRESS`
  * `-var 'NAME=VALUE'`
  * `-var-file=FILE`
* [`show`](../cli/commands/show.mdx)
  * `-no-color`
  * `-json`
  * (both with and without a plan file)
* [`providers`](../cli/commands/providers/index.mdx) (with no subcommand)
* [`providers lock`](../cli/commands/providers/lock.mdx)
  * `-fs-mirror=PATH`
  * `-net-mirror=URL`
  * `-platform=OS_ARCH`
* [`providers mirror`](../cli/commands/providers/mirror.mdx)
  * `-platform=OS_ARCH`
* [`providers schema`](../cli/commands/providers/schema.mdx)
  * `-json`
* [`fmt`](../cli/commands/fmt.mdx)
  * `-list=false`
  * `-write=false`
  * `-diff`
  * `-recursive`
  * `-check`
* [`version`](../cli/commands/version.mdx)
  * `-json`
* [`output`](../cli/commands/output.mdx)
  * `-no-color`
  * `-json`
  * `-raw`
* [`taint`](../cli/commands/taint.mdx)
  * `-allow-missing`
  * `-lock=false`
  * `-lock-timeout=DURATION`
  * `-ignore-remote-version`
* [`untaint`](../cli/commands/untaint.mdx)
  * `-allow-missing`
  * `-lock=false`
  * `-lock-timeout=DURATION`
  * `-ignore-remote-version`
* [`force-unlock`](../cli/commands/force-unlock.mdx)
  * `-force`
* [`state list`](../cli/commands/state/list.mdx)
  * `-id=ID`
* [`state pull`](../cli/commands/state/pull.mdx)
* [`state push`](../cli/commands/state/push.mdx)
  * `-force`
  * `-lock=false`
  * `-lock-timeout=DURATION`
* [`state show`](../cli/commands/state/show.mdx)
  * `-ignore-remote-version`
* [`login`](../cli/commands/login.mdx)

For commands or options not in the above list, we will still avoid breaking
changes where possible, but can't promise full compatibility throughout the
v1.x series. If you are building automation around OpenTofu, use only the
commands above to avoid the need for changes when upgrading.

Please note that although OpenTofu's internal logs (via the `TF_LOG`
environment variable) are available in a JSON format, the particular syntax
or structure of those log lines is _not_ a supported integration interface.
The logs are available as JSON only to help with ad-hoc filtering and
processing of logs by OpenTofu developers.

### Commands That Might Change

All of the following commands and their subcommands/options are _not_ subject
to compatibility promises, either because we have existing plans to improve
them during the v1.x series or because we are aware of shortcomings in their
design that might require breaking changes for ongoing maintenance.

While you can freely use these commands when running OpenTofu interactively
as long as they remain supported, we don't recommend using them as part of
any automation unless you are willing to potentially update that automation
when upgrading to a later v1.x release.

* `destroy` (consider `tofu apply -destroy` instead)
* `console`
* `get` (consider `tofu init` instead)
* `graph`
* `import`
* `push`
* `refresh` (consider `tofu apply -refresh-only` instead)
* `state mv`
* `state replace-provider`
* `state rm`
* all subcommands of `workspace` (and its deprecated alias `env`)

While we do intend to retain support for the main use-cases associated with
these commands in future releases, we cannot promise to retain the exact
command names or options used to meet those use-cases.

## How We Will Keep These Promises

### Automated Regression Testing

The OpenTofu codebase includes various unit and integration tests intended to
help us to notice accidental behavior regressions before they ship in a stable
version.

However, OpenTofu is a relatively complex system with many different features
that can interact in interesting ways. In the past we've seen reports of
behavior differences that appeared only when combining two or more features in
a way we hadn't previously anticipated or written automated tests for.

In each case we have both implemented a change to resolve the compatibility
problem _and_ added one or more integration tests representing the behavior
of that combination of features. We intend to continue this approach, so we can
improve OpenTofu's test coverage over time.

### Prerelease Versions

We intend that most accidental changes in behavior covered by these promises
will be caught by existing tests. However, we also accept that our test suite
can never have perfect coverage of all possible feature interactions or other
edge cases, and so we aim for each significant change to be included in both
alpha and beta releases before eventual inclusion in a final release.

For minor releases we will typically also issue at least one release candidate
prior to the final release. A release candidate represents that planned
development is concluded and that we've fixed any regressions reported based
on the alpha and beta releases, and thus the final release that follows should
typically match exactly or almost exactly its most recent release candidate.

### Regressions in Final Releases

For more obscure combinations of features it is possible that a regression
could be undetected during prerelease the prerelease periods and thus included
in a final release.

If someone finds and reports such a regression soon after its release then we
will treat it as a bug and fix it to restore the previous behavior in future
releases, unless there is a very significant justification such as a security
advisory. In these cases, we'll typically recommend anyone affected by the
regression remain on the previous version until the problem is fixed and then
skip forward directly to the new release containing that fix.

You can minimize the risk of being affected by missed regressions in final
releases by proactively testing modules against alpha, beta, and release
candidate packages. We recommend doing so only in isolated development or
staging environments rather than against your production infrastructure. If you
find a change in behavior in a prerelease build that seems contrary to the
promises in this document, please open an issue in OpenTofu's GitHub
repository to discuss it.

### Late-reported Regressions

In the most extreme case, there may be a regression with a combination of
features that is so rare that it remains undetected for a long time.

After a change has been included in more releases it becomes increasingly
likely that other users will have depended on the newer behavior and thus we
will need to make a tradeoff to decide whether restoring the behavior would
have a greater negative impact than retaining the new behavior. We will always
make this decision with due consideration to the implications of each unique
situation.

You can minimize the risk of your modules being affected by late-reported
regressions by upgrading promptly to new minor and patch releases of OpenTofu
and reporting any compatibility problems you encounter in OpenTofu's GitHub
repository.

### Pragmatic Exceptions

We are making the promises above in good faith, with the intent that your
investment in writing OpenTofu modules or automation will not be invalidated
by future changes to OpenTofu. However, broad promises like the above can't
possibly cover all nuances of practical problems that might arise as we
continue to develop OpenTofu.

For that reason, there are some situations where we may still need to make
changes that may impact existing modules or automation:

* Security problems: We may become aware of a design problem that has an
  important security impact. Depending on our determination of the associated
  risk, we may choose to break compatibility to achieve a more secure system.
* External Dependencies: OpenTofu's behavior depends on interfaces provided
  by external codebases, including your chosen operating system and including
  some remote network services for situations such as module and provider
  installation. These external systems can change outside of our control,
  including potentially removing or changing features that OpenTofu's own
  features depend on. In that case, if there is no suitable replacement
  mechanism then we may need to change OpenTofu's design to work within the
  new constraints.
* Opt-in Compatibility Breaks: The design of a language new feature may require
  changing the behavior or configuration representation of an existing feature.
  If so, we will typically make the new feature opt-in only in order to avoid
  breaking existing modules, but if you change your module to opt in to the
  new feature then you may also then be required to change other parts of your
  configuration to work with the new language design.
* Bugs in New Features: If we introduce a new feature to OpenTofu and the
  initial implementation has problems that cause it to not match the documented
  design intent at release, we may make a follow-up release that corrects
  the implementation to match the documented design, even if that represents
  a minor compatibility regression compared to the initial implementation.
  However, once a feature is well-established and in common use we will usually
  defer to the implemented behavior and instead change the documentation to
  reflect it.
* Regressions in Existing Features: If we learn that a new OpenTofu release
  includes a regression for an existing feature that wasn't detected during
  the development and prerelease periods, and that learning comes promptly
  after the new release, we will typically restore the previous behavior at
  the expense of technically therefore breaking compatibility with the behavior
  of the new release, under the assumption that more users will have systems
  affected by the regression than will have systems depending on the
  newly-introduced behavior.
* Late-reported regressions: As described in the previous section, if we
  learn that there was an unintentional regression of a rarely-used feature or
  combination of features in a much earlier release then restoring the previous
  behavior may appear as a regression to later adopters. If we believe that
  fixing the regression would affect more users than the regression itself
  affects then we may choose to accept the regression as the new promised
  behavior.
* Situations we cannot anticipate: Although we've made an effort to consider
  various specific exceptional situations here, OpenTofu and its development
  process are not isolated from broader context, and so we must consider that
  there may be situations that we cannot possibly anticipate that would affect
  the future of OpenTofu. In those situations, we will always do our best to
  find a course of action that will minimize as much as possible the impact to
  existing modules and automation.

Our intent with these pragmatic exceptions is only to acknowledge that there
will always be situations that general compatibility promises cannot address.
We will use these exceptions only with due consideration and as a last resort.
