What is trust decanting, and can a trustee do it without telling the beneficiaries?

The condition that answers your question is notice. Prob. Code § 19507 requires the authorized fiduciary to give notice not later than 60 days before the decanting power is exercised. The notice goes to the living settlors of the first trust, to the qualified beneficiaries, to anyone holding a presently exercisable power of appointment, to anyone holding a right to remove or replace the fiduciary, to the other fiduciaries of the first trust and the fiduciaries of the second trust, and to the Attorney General where a charitable interest is involved. Sixty days before, not after, and not at the next accounting. A trustee who decants quietly has not merely created a fight with the family; he has skipped a statutory requirement. The general duties still apply on top. Under Prob. Code §§ 16060–16062 a trustee must keep beneficiaries reasonably informed of the trust and its administration, report on reasonable request, and account at least annually, on termination, and on a change of trustee. A trustee who wants more protection than notice alone gives can petition the probate court for instructions under Prob. Code § 17200 and have the proposed change blessed in advance, and a beneficiary who believes a decanting was improper uses that same statute to put the question in front of a judge.