According to Google Cloud Storage documentation, the soft-delete policy is a feature enabled by default on new buckets (starting in 2024) to protect against accidental or malicious deletion. It retains deleted objects for a specified retention period (default is seven days). For workloads involving large files—such as the video files Cymbal uses for Vertex AI training—this policy can lead to unexpected cost spikes.

When soft-delete is active, objects that are deleted are not immediately removed from the billing cycle; instead, they continue to incur charges at the same rate as "live" objects until the retention period expires. In an AI training environment where datasets are frequently updated, replaced, or temporary "scratch" files are created and deleted, the volume of soft-deleted bytes can quickly double or triple the effective storage footprint.

Options B and D are incorrect because moving from dual-region or multi-region to a single region would actually reduce storage costs, as regional storage is priced lower. Option A is incorrect because disabling the policy would stop the retention of deleted bytes, thereby lowering the bill. Therefore, checking for an active or recently enabled soft-delete policy is the standard troubleshooting step for sudden increases in storage costs associated with high-churn, large-file datasets.