---
version: "v1.0.5"
category: "experiments-updated"
---

#### `cas` — `mutable` attribute on `terraform`, `unit`, and `stack` blocks

A new `mutable` attribute opts a block out of CAS hardlinking when its source is fetched through CAS. With `mutable = true`, files materialized into `.terragrunt-cache` (for `terraform`) or `.terragrunt-stack` (for `unit` and `stack`) are copied from the CAS store and the working tree is editable.

The default is `false`. Files are materialized read-only so an accidental edit cannot reach back into the shared CAS store.

```hcl
terraform {
  source  = "git::https://github.com/acme/infrastructure-modules.git//vpc?ref=v1.0.0"
  mutable = true
}
```

The flag is orthogonal to `update_source_with_cas` and has no effect when content is fetched through the standard download path, which already produces an independent copy.
