It adds another provider that you have to trust with your data. Previously the assumption is that AWS was securely handling your data and you may have the data on AWS to start with anyways. Now you have two providers handling your data which doubles your risk if you trust them equally. If you think AWS has more robust data controls than Anthropic then it more than doubles your risk.

You may also have data management requirements such as allowed storage and transit countries as well as various certifications and contracts that you now need to extend to the second data processor.

Basically if you are already using AWS just adding the AWS-only bedrock model is legally easy and doesn't really change your security posture. If you need to now also log your data to Anthropic it makes the choice much more complicated.