On the Sculpin blog Beau Simensen has posted an update about a change in how the project will be released in the future, most notably deprecating the phar release and switching to an embedded Composer installation.

If you are currently using a globally installed phar distribution for Sculpin you should migrate to a per-project Composer installed version of Sculpin as soon as you can. [...] Any plans for Sculpin 3 would have required reworking the phar build and distribution process

In typical programmer fashion, I let myself get bogged down in the details of eventually needing to deploy Sculpin 3 phar builds rather than working on Sculpin 3. What little time I had to spend on Sculpin last year was sunk on solving this problem. [...] The last officially available Sculpin phar is not compatible with PHP 7.

He talks about his earlier goals to make v3 of Sculpin PHP 7-only but, in the process of the work to get to that point, several roadblocks came up preventing it. He talks about self-updating phars and finally realizing that, for the good of the project, a move to the embedded Composer setup is the best method for keeping dependencies in sync. He ends the post with the steps you'll need to take to migrate from the phar release to the managed version and an example commit of how the Sculpin site itself was migrated.