Gentoo provides a package called app-admin/ansible for Ansible. To install it, just run:

❯ sudo emerge --ask app-admin/ansible

Note that unlike Ansible package on CentOS/Fedora, there is no default ansible.cfg provided with the Gentoo Ansible package.

❯ ansible --version
ansible 2.9.9
  config file = None
  configured module search path = ['/home/kenno/.ansible/plugins/modules', '/usr/share/ansible/plugins/modules']
  ansible python module location = /usr/lib/python3.7/site-packages/ansible
  executable location = /usr/lib/python-exec/python3.7/ansible
  python version = 3.7.7 (default, May  9 2020, 19:52:18) [GCC 9.2.0]