# Upgrading to Varnish 7.4

## Important VCL Changes

When upgrading from Varnish-Cache 7.3, there is only one breaking change to consider in VCL:

The `Content-Length` and `Transfer-Encoding` headers are now protected, they can neither be changed nor unset. This change was implemented to avoid de-sync issues from accidental, inadequate modifications of these headers.

For the common use case of `unset (be)req.http.Content-Length` to dismiss a request body, `unset (be)req.body` should be used.

## Parameter Changes

The new `varnishd` parameter `startup_timeout` now specifically replaces `cli_timeout` for the initial startup only. In cases where `cli_timeout` was increased specifically to accommodate long startup times (e.g. for storage engine initialization), `startup_timeout` should be used.

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