Letters to expert witnesses and AI security: what instructing an expert gives away in ChatGPT or Claude.
A letter of instruction to an expert sets out the dispute, the documents and the questions the court needs answered, and the Expert Witness Code says it may be annexed to the report. That makes it tempting to polish in ChatGPT or Claude, and risky: it also carries the weak points in the client’s own records and documents produced on subpoena. The Supreme Court of NSW has a practice note on generative AI that speaks to both. This page marks every item in a typical letter to a metallurgist and shows how the same letter is drafted on Ermos inside the firm.
The letter of instruction to an expert
Sent after proceedings are on foot, when the case turns on a technical question, and later relied on to show what the expert was asked and told.
Carrick Doyle Lawyers
30 October 2026
Dr Linh Tran, Tran Materials Consulting, Homebush NSW2
By email
Re: Pacific Rim Fabrication Pty Ltd v Tarrangower Marine Pty Ltd, Supreme Court of NSW, Equity Division, 2026/003561201: instructions to expert
Dear Dr Tran,
Background. Our client fabricated 36 hull bracket assemblies for the defendant under Purchase Order KM-2205 and has sued for $412,860.00 unpaid. The defendant says that brackets B-07, B-19 and B-22 cracked during sea trials on 18 September and that the cause was defective welding. Our client says the cracking followed installation, including bolt loads applied at the defendant’s shipyard.3
A difficulty. Our client’s inspection sheet for B-19 is unsigned, and its non-destructive testing report for the second batch was issued four days after dispatch. We do not yet know why. Please assume nothing about either, and tell us what the records show.4
Questions.
- What is the most likely cause of the cracking in B-07, B-19 and B-22: a weld defect, or loads applied after delivery?5
- Do the welds in the six brackets we have photographed conform to clause 4.2 of the purchase order?5
- Is the crack pattern consistent with over-tightening at installation?5
Documents. We enclose the class surveyor’s report produced to us on subpoena on 26 October. It is subject to the implied undertaking and may be used only for this proceeding.6 The defendant has foreshadowed a cross-claim of about $640,000 for the vessel’s downtime. You are not asked to address it.7
The Code. Please read the Expert Witness Code of Conduct (Schedule 7 to the Uniform Civil Procedure Rules 2005), enclosed. Your report may not be received in evidence unless you acknowledge that you have read the Code and agree to be bound by it. It must state your qualifications, the facts and assumptions on which each opinion is based, and your reasons.8
Generative AI. Practice Note SC Gen 23 provides that Gen AI must not be used to draft or prepare the content of an expert report without the Court’s prior leave, and requires us to draw that to your attention. Please do not use it for any part of your report.9
Timetable. Your report is due by 4 December 2026. Your estimate is $14,500 plus GST; please tell us before it is exceeded.10
Yours sincerely,
Eleanor Vance
An invented letter. The file number and document references are invented. Hover or tap any highlighted item for the analysis; the full list is below.
What leaves the firm
- 1The proceedings and the file number
Named parties, the court and a file number. With the matter identified, the whole dispute is searchable. Rule 9 confidentiality guide.
Frontier Models (ChatGPT, Claude) A live proceeding identified on a third party’s servers Ermos Edge Stays on your instance in Australia; leaves only inside a permitted excerpt, per question, to the named provider Ermos Dominion Stays on the unit in your office - 2The expert
A named professional engaged on a live proceeding. Her personal information, and a fact the other side may want to know before the report is served. Privacy Act guide.
Frontier Models (ChatGPT, Claude) An expert engaged on a live matter identified Ermos Edge Stays on your instance in Australia; leaves only inside a permitted excerpt, per question, to the named provider Ermos Dominion Stays on the unit in your office - 3The client’s account of the dispute
The product, the claim, the defendant’s allegation and the client’s theory of what went wrong. Confidential to the client, and communications made for the dominant purpose of litigation. Legal privilege guide.
Frontier Models (ChatGPT, Claude) Privileged account of the dispute transmitted; on consumer tiers it can train future models Ermos Edge Stays on your instance in Australia; leaves only inside a permitted excerpt, per question, to the named provider Ermos Dominion Stays on the unit in your office - 4A gap in the client’s own records
An unsigned inspection sheet and a late test report, with the instruction not to assume. The firm’s candid view of the client’s weakest point, which the other side would like to read. Legal privilege guide.
Frontier Models (ChatGPT, Claude) The client’s weakest point now on a third party’s servers Ermos Edge Stays on your instance in Australia; leaves only inside a permitted excerpt, per question, to the named provider Ermos Dominion Stays on the unit in your office - 5The questions
What the firm asks the expert reveals the theory of the case: that loads at the defendant’s shipyard caused the cracks. The questions are the strategy. Legal privilege guide.
Frontier Models (ChatGPT, Claude) The case theory transmitted before the expert has answered Ermos Edge Stays on your instance in Australia; leaves only inside a permitted excerpt, per question, to the named provider Ermos Dominion Stays on the unit in your office - 6Documents produced on subpoena
A class surveyor’s report obtained by compulsory process. Paragraph 9A of Practice Note SC Gen 23 says material produced on subpoena, and material under the implied (Harman) undertaking, must not be entered into any Gen AI program unless the practitioner is satisfied of the conditions it lists. Legal privilege guide.
Frontier Models (ChatGPT, Claude) Subpoenaed material transmitted, contrary to the practice note’s starting point Ermos Edge Only permitted excerpts leave, per question, to a named Australian provider that keeps nothing; the practitioner must still be satisfied of the conditions in paragraph 9A Ermos Dominion Stays on the unit in your office - 7The other side’s foreshadowed claim
A cross-claim figure and its basis. Information about an opponent’s position that the firm holds for the client. Rule 9 confidentiality guide.
Frontier Models (ChatGPT, Claude) The opponent’s foreshadowed claim transmitted Ermos Edge Stays on your instance in Australia; leaves only inside a permitted excerpt, per question, to the named provider Ermos Dominion Stays on the unit in your office - 8The Code of Conduct paragraph
A summary of Schedule 7 and rule 31.23 of the Uniform Civil Procedure Rules. Public rules with no client or party in them.
Frontier Models (ChatGPT, Claude) Public rule text; pasting it exposes nothing Ermos Edge Public text either way Ermos Dominion Public text either way - 9The generative AI paragraph
A summary of paragraphs 20 and 24 of the practice note. A public document. Paragraph 20 concerns the expert’s report; the letter of instruction is not the report.
Frontier Models (ChatGPT, Claude) Public practice note text; pasting it exposes nothing Ermos Edge Public text either way Ermos Dominion Public text either way - 10The timetable and the fee estimate
A due date and the expert’s cost estimate. Low sensitivity alone, but it names the expert and the matter.
Frontier Models (ChatGPT, Claude) Low value alone, but it names the expert and the matter Ermos Edge Low value alone; the route changes little Ermos Dominion Low value alone; the route changes little
What happens in Frontier Models (ChatGPT, Claude)
- The whole document is transmitted to the provider’s servers. On personal plans the user cannot choose where it is stored or processed, and for the major providers that has generally meant outside Australia, under that country’s legal process. Some business plans offer storage in Australia, but the provider still receives the content.
- On consumer tiers, prompts can be retained and used to train future models.
- The provider’s staff and systems can reach the content under the provider’s own policies.
- Once sent, the firm no longer controls it. Retention and deletion happen on the provider’s terms.
The same document on Ermos
Ermos Dominion
The document is drafted on a unit in your office, from your own templates and the matter file. Every marked item stays on the unit, which keeps working with the internet switched off. Nothing in it is transmitted to an AI provider, so there is no disclosure to analyse: the confidentiality work is the same as for your file server.
Ermos Edge
Your documents, the index and your access boundaries stay on your own instance in an Australian data centre. When a staff member asks for this draft, only their question and the excerpts they are permitted to see go to a named Australian provider, who is contractually barred from keeping the content or training any model on it. Nothing is processed outside Australia.
| Frontier Models (ChatGPT, Claude) | Ermos Edge | Ermos Dominion | |
|---|---|---|---|
| Where the document is processed | Provider servers, generally offshore on personal plans | Your instance in an Australian data centre; answers generated in Australia | The unit in your office |
| Who can read it | Provider staff and systems, under policy | Your staff, within the boundaries you set. The named Australian provider processes only permitted excerpts, under contract, and keeps nothing | Your staff only |
| Is it kept | On the provider’s terms | Kept on your instance; the provider is barred from retaining it | Stays on the unit |
| Can it train a model | On consumer tiers, yes | No, by contract | Only your own unit learns from it, on your hardware |
Part of AI data leakage in law firms. See how this works in practice: Matter work on Ermos.
Common questions
Do ChatGPT and Claude use the information in a letter of instruction to an expert?
Is it safe to paste a letter of instruction to an expert into ChatGPT or Claude?
Does deleting the chat remove a letter of instruction to an expert from ChatGPT or Claude?
How can a law firm use AI for a letter of instruction to an expert without sending it to ChatGPT or Claude?
What does the NSW Expert Witness Code require of an expert's report?
Can an expert use generative AI to write a report for the Supreme Court of NSW?
Why does the practice note matter for documents sent to an expert?
See Dominion answering from your own documents.
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