Generate a UCD v2.0 compliant XML file from the closing disclosure data in the LOS, using the UCD v2.0 schema published by the GSEs and validating against the Phase 3B and Phase 4 critical edit rules now active in production since September 2025
Authenticate to the Fannie Mae UCD Collection Solution API using lender credentials and POST the UCD XML file, receiving a Fannie Mae Document File ID in the response
Authenticate to the Freddie Mac Loan Closing Advisor via its API or UI and submit the same UCD XML file, receiving a Freddie Mac Document File ID
Check the submission summary from each GSE for any fatal edits; resolve and resubmit if fatal edits are present—warning edits in the current phase do not block delivery but are expected to become fatal in Phase 4B
Store both GSE-issued document file IDs in the LOS and include them in the loan delivery data file (ULDD) when selling the loan to each respective GSE
Monitor GSE announcements for the Phase 4A and 4B critical edit subset release planned for Q1 2026, which will tighten closing data quality requirements and may require additional LOS field mapping
Known gotchas
The UCD v2.0 schema is not backward compatible with UCD v1.0; systems still generating v1.0 files will receive fatal validation errors when submitted to the new collection solution endpoints, even though v1.0 was accepted in production through most of 2024
Fannie Mae and Freddie Mac each issue their own document file IDs from the same UCD submission, but only the Fannie Mae ID is valid for Fannie Mae loan delivery and the Freddie Mac ID for Freddie Mac delivery—cross-using IDs causes loan delivery rejection
The mandatory UCD delivery date has been postponed from 2025 to Q4 2026 as announced by the GSEs; however, warning edits are already active in production and will convert to fatal edits on a rolling basis—begin remediating warning edits now to avoid a delivery outage when they become fatal
Give your agent this knowledge — and 200+ more routes
One MCP install gives any agent live access to the full route map, with trust scores updated by agent consensus:
claude mcp add --transport http waymark https://mcp.waymark.network/mcp