This is a Tautoru view, not a settled position.
Confidentiality is a duty, and it is not the same thing as privilege. A New Zealand lawyer owes it to every client under the Conduct and Client Care Rules (chapter 8): client information is kept confidential and used only for the client's purposes. Confidentiality is also owed more widely — by contract, by an undertaking, or simply because information was given to you in confidence. The question here is narrower than "is this confidential?" It is whether putting confidential material into an AI tool breaches the duty to keep it so.
Usually it does not. A duty to maintain confidentiality is not breached merely by using a third-party platform to hold or process the material — no more than by using an off-site document store, a cloud document-management system or an external IT contractor. What matters is that the material stays confidential in fact. So the duty is not breached provided you do nothing that suggests you are giving up that confidentiality, and you do not allow or invite other people to look at the material. Using a service on terms of confidence, for the limited purpose of doing your work, is consistent with the duty; making the material readable by others is not.
That is why the plan and the settings matter. A plan that does not train on your inputs, limits retention and controls access keeps the material confidential — it is held for you and processed for you, and no one else is given access. A consumer account that may train on what you type, or whose conversations the provider's staff may review, is a different proposition: there you may be allowing others to see the material, which is the thing the duty guards against. Where the confidentiality is owed to someone other than your own client — the other side, a counterparty, anyone who gave you information under an NDA — the same test applies, and the terms of that obligation may require their authority before the material goes anywhere.
Court-ordered restrictions are different again, and they need to be considered carefully. A suppression order, a confidentiality order, sealed material, or an undertaking given to the other side can be an absolute bar — not because confidentiality might be lost, but because the order or undertaking itself prohibits the disclosure or use. Some are framed so that any disclosure beyond a defined purpose is a breach, and entering the material into an external tool could cross that line whatever the platform's confidentiality. Read the specific order or undertaking before you act; do not assume a "secure" tool answers it.
Our view
A duty to keep something confidential is not, by itself, a reason you cannot use a confidential AI tool. The duty is met by keeping the material confidential in fact and not letting others see it — which a no-training, access-controlled plan does. The real work is choosing such a plan, obtaining any authority the obligation requires, and checking separately for any court order or undertaking that bars the use outright. How that applies to your matter is your judgment, on your facts.