Kant says that some duties generated by the categorical imperative are absolute-they are perfect duties. So regarding the perfect duty not to lie, Kant would insist that lying is:

not permitted under any circumstances.

Explanation:

According to Immanuel Kant, the categorical imperative is a philosophical concept in deontological moral philosophy. It is the moral obligation of the person which is unconditionally bonded at any circumstances and is not dependent on the person's choices.

According to Kant, some works or duties are absolute and perfect duties and according to the deontological moral philosophy one is not permitted or advised to lie at any circumstances regarding the work which is generated by categorical imperative.