C# ISO 20022 Library synced to September 4, 2026 snapshot

September 25, 2026 by Jeff Ward (Beneficial Strategies)

Right alongside the MCP server’s own update to the September 4, 2026 ISO 20022 snapshot, we’ve brought the C# ISO 20022 Library up to date as well, moving up from the previous June 26, 2026 sync. This one’s shipping as v0.7.0-alpha on NuGet, and it’s a purely additive update: zero breaking changes, zero removed types, zero obsoleted types this cycle.

At a glance

3,340 total message definitions (+11)
24,275 total supporting structures (+40)
29 new external code sets
7 new message components
2 new choice types
11 new top-level messages
0 breaking changes
9,129 tests passing, 0 failures, across both net8.0 and net10.0

What’s new

The biggest functional addition this cycle is a brand-new message family for Standing Settlement Instructions (reda) — the cash/securities settlement routing details counterparties exchange and maintain. Four new messages give consumers a complete lifecycle for managing them:

StandingSettlementInstructionV01 — create or update an SSI
StandingSettlementInstructionCancellationV01 — cancel one
StandingSettlementInstructionDeletionV01 — delete one
StandingSettlementInstructionStatusAdviceV01 — report status on any of the above

Alongside that, seven new DTCC market-practice supplementary messages (supl) extend existing ISO corporate-actions messages — cancellation advice, movement confirmation/preliminary advice, instruction status advice, and CSD/eligible-balance asset-servicer data — with DTCC-specific elements layered on top of the core ISO schema.

On the code set side, 29 new external code sets landed, the largest cluster being the ExternalPostTradeCode family (a base type plus three scoped restrictions) covering 38 known post-trade processing codes, alongside new code sets for prospectus document types, benchmark type/significance, decision-status-update reasons, and account-verification reasons. Eight other code sets simply graduated from Provisionally Registered to fully Registered status this cycle — no consumer-facing change there.

One correction worth knowing about

ISO corrected a typo in one of its own reason codes this cycle: BE01’s name was InconsistenWithEndCustomer (missing a “t”) and is now InconsistentWithEndCustomer. It touches six related code sets — ExternalStatusReasonCode, ExternalStatusReason1Code, ExternalMandateReasonCode, ExternalMandateReason1Code, ExternalReturnReasonCode, and ExternalReturnReason1Code. The wire-level code value (BE01) is completely unchanged — this only affects you if your code references the named C# constant directly rather than the code value itself.

FluentValidation companion package, unaffected

The FluentValidation companion package was checked against this same snapshot: the pain and pacs business areas remain 100% full-spec validator coverage, untouched by anything in this cycle. No validator updates were needed.

Get it from NuGet

This release is tagged v0.7.0-alpha — a pre-release version, so you’ll need the --prerelease flag (or an exact version pin) to pick it up:

dotnet add package BeneficialStrategies.Iso20022 --prerelease
dotnet add package BeneficialStrategies.Iso20022.FluentValidation --prerelease

Source, issue tracker, and full documentation live on GitHub.