boto/boto3 · error · UnknownAPIVersionError

The ' ' resource does not support an API version of: Valid…

Error message

The '{service_name}' resource does not support an API version of: {bad_api_version}
Valid API versions are: {available_api_versions}

What it means

`UnknownAPIVersionError` is raised when `Session.resource(service_name, api_version=...)` references an API version that has no `resources-1` data file for that service. boto3 lists the valid versions in the message. This happens because a resource model exists for the service, but not for the specific (often outdated or forward-dated) version you requested. Note that resource API versions and client API versions can legitimately differ, so pinning requires care.

Solutions

Omit `api_version` to let boto3 select the latest supported resource version.
Pick a version from the message's `available_api_versions` list (e.g. via `boto3.session.Session()._loader.list_api_versions(name, 'resources-1')`).
Upgrade boto3 — newer versions add more API version files.
Reinstall boto3 if a version that should exist is missing (corrupt install).

Example fix

# before
boto3.resource('s3', api_version='2004-01-01')  # UnknownAPIVersionError

# after
boto3.resource('s3')  # latest resource API version
# or pick from the listed valid versions, e.g.
boto3.resource('s3', api_version='2006-03-01')

Defensive patterns

Strategy: validation

Validate before calling

def safe_resource(session, service, api_version=None):
    versions = session._loader.list_api_versions(service, 'resources-1')
    if api_version and api_version not in versions:
        api_version = None  # let boto3 pick the latest
    return session.resource(service, api_version=api_version)

Type guard

def api_version_supported(session, service, version) -> bool:
    return version in session._loader.list_api_versions(service, 'resources-1')

Try / catch

from boto3.exceptions import UnknownAPIVersionError
try:
    res = session.resource(service, api_version=v)
except UnknownAPIVersionError:
    res = session.resource(service)  # default latest

Prevention

Avoid pinning api_version for resources unless reproducibility requires it.
Source valid versions from list_api_versions(service, 'resources-1').
Upgrade boto3 to gain newer resource API version files.

When it happens

Trigger: Calling `boto3.resource('s3', api_version='2004-01-01')` (a version with no resource data) or `api_version='2099-01-01'` (does not exist); pinning to a version copied from a different service's docs; using a version string that is a client-only API version.

Common situations: Hard-coding an old api_version for reproducibility that predates the resource model; mistyping the date format; environment with a partial boto3 install missing some version files.

Related errors

AI-assisted analysis of boto/boto3@6e10b029c1 (2026-08-11). Data as JSON: /api/errors/0f4defdda727d7ff. Report an issue: GitHub.

Appendix: source

Thrown at boto3/session.py:441

        """
        try:
            resource_model = self._loader.load_service_model(
                service_name, 'resources-1', api_version
            )
        except UnknownServiceError:
            available = self.get_available_resources()
            has_low_level_client = (
                service_name in self.get_available_services()
            )
            raise ResourceNotExistsError(
                service_name, available, has_low_level_client
            )
        except DataNotFoundError:
            # This is because we've provided an invalid API version.
            available_api_versions = self._loader.list_api_versions(
                service_name, 'resources-1'
            )
            raise UnknownAPIVersionError(
                service_name, api_version, ', '.join(available_api_versions)
            )

        if api_version is None:
            # Even though botocore's load_service_model() can handle
            # using the latest api_version if not provided, we need
            # to track this api_version in boto3 in order to ensure
            # we're pairing a resource model with a client model
            # of the same API version.  It's possible for the latest
            # API version of a resource model in boto3 to not be
            # the same API version as a service model in botocore.
            # So we need to look up the api_version if one is not
            # provided to ensure we load the same API version of the
            # client.
            #
            # Note: This is relying on the fact that
            #   loader.load_service_model(..., api_version=None)
            # and loader.determine_latest_version(..., 'resources-1')

View on GitHub (pinned to 6e10b029c1)