Custody
Every AI decision on a loan file is recorded, gated, and chained — so when a GSE, an examiner or an investor asks what your AI did and what stopped it going wrong, the answer is an artifact they can verify themselves rather than an assurance they have to accept.
Fannie Mae Lender Letter LL-2026-04 took effect on 6 August 2026. Seller/servicers using AI or ML in origination or servicing must govern its development and use, extend no-less-protective governance to their vendors, and on Fannie Mae’s request promptly disclose the types of AI/ML in use, the purpose and manner of that use, and the safeguards implemented to mitigate the risks.
There are two ways to answer that request: a document describing what you intend to happen, or a record of what did happen that the person asking can verify for themselves. This is the second.
The letter specifies no record schema and does not require signed or append-only logs — that design is ours, not Fannie Mae’s. Read the letter: singlefamily.fanniemae.com → Lender Letter LL-2026-04One synthetic loan file through five AI steps. Everything here — borrower, employer, documents, loan number — is fabricated. The hashes are not: your browser recomputes every one of them from the record contents when you press verify.
The packet for one loan: every decision, in order, including the ones that were rejected. It carries the public key and the records, so the recipient verifies it without access to any of the lender’s systems — which is what turns a disclosure into evidence.