Zero Data Retention does not mean zero information retention. First, this whole discussion regards AWS Bedrock's straightforward policy for users of OpenAI GPT-5.4 and GPT-5.5 models and Anthropic Claude Fable 5 saying "[inputs and outputs will be retained for up to 30 days](https://docs.aws.amazon.com/bedrock/latest/userguide/abuse-d... )." That's plenty of time for a model training run using those inputs/outputs and, once the information is encoded into model weights, the original training data can be deleted to meet the ZDR contract.
For models without the 30-day retention clause, it's still possible for AWS to route inputs and outputs through a dynamic training system to encode the information into model tensors and then toss out the original "data".
Edit: linkify