Use the aws:PrincipalOrgID global condition key in the S3 bucket policy to allow only principals from the Organization is the correct option because it lets the bucket policy allow access only for principals whose accounts belong to the specified AWS Organization and it removes the need to maintain a manual list of account IDs.

Using aws:PrincipalOrgID in the S3 bucket policy lets you compare the principal account owner s organization ID to a single value so access automatically follows organization membership changes. This approach scales to many accounts and avoids ongoing operational overhead of updating policies as accounts are added or removed.

Build an attribute-based access control model by tagging each account as in-organization and reference those tags in the S3 bucket policy is impractical because it depends on consistent tag application and governance across all accounts and it creates extra operational work to keep tags accurate.

AWS Resource Access Manager does not apply because RAM cannot share or restrict access to S3 buckets with a resource policy and it is not intended to control S3 resource access in this way.

Place all external accounts in an Organizational Unit and attach a Service Control Policy that denies access to the bucket is not effective because service control policies act as account level guardrails and do not function as S3 resource policies and they cannot control access for non member accounts.

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