The "hash-policy" command:

Usage: fossil hash-policy ?NEW-POLICY?

Query or set the hash policy for the current repository.  Available hash
policies are as follows:

  sha1              New artifact names are created using SHA1

  auto              New artifact names are created using SHA1, but
                    automatically change the policy to "sha3" when
                    any SHA3 artifact enters the repository.

  sha3              New artifact names are created using SHA3, but
                    older artifacts with SHA1 names may be reused.

  sha3-only         Use only SHA3 artifact names.  Do not reuse legacy
                    SHA1 names.

  shun-sha1         Shun any SHA1 artifacts received by sync operations
                    other than clones.  Older legacy SHA1 artifacts are
                    allowed during a clone.

The default hash policy for existing repositories is "auto", which will
immediately promote to "sha3" if the repository contains one or more
artifacts with SHA3 names.  The default hash policy for new repositories
is "shun-sha1".