As of May 2026
The question that broke our position model was simple: what was the cash position at 11:47am? For any timestamp that did not land on a snapshot, the honest answer was an interpolation between the last two saved states.
When I was the enterprise architect over treasury and payments, that question had an embarrassing answer. We interpolated between the last two saved states and hoped nobody asked for the math. Real-time rails turned that interpolation from a quirk into a liability.
The instinct is to sample more often. I would go the other way and stop storing a position at all. The position becomes a fold over the event log, and 11:47am stops being a guess and becomes a replay.
Why interpolation became a liability
RTP cleared 128 million transactions worth 480 billion dollars in Q1 2026, per The Clearing House, and FedNow runs around the clock with a per-transaction limit that was raised to 10 million dollars in November 2025. Between a 10am and a 2pm snapshot the position now moves hundreds of times. The drift that used to stay inside the noise of ACH batch windows is now the position itself, so a model that interpolates between saved states is not approximating the answer anymore. It is hiding it.
The fold, not the sample
Make every rail event an immutable entry. The position is a fold over that log, computed on demand rather than read from a saved guess. The 11:47am question stops being an interpolation and becomes a replay, derived from the events that actually happened.
Q1 2026 RTP
128M / $480B
RTP cleared 128 million transactions worth $480 billion in Q1 2026 (The Clearing House).
The model fix
Event log
stop storing a position - make each rail event immutable and fold the log into the answer.
The mandate
PS25/12
FCA safeguarding, in force 7 May 2026, requires daily reconciliation of safeguarded funds.
Why the regulator is now asking the same question
This matters more than it used to because someone with subpoena power is now asking it. The FCA’s safeguarding overhaul has been in force since 7 May 2026 under Policy Statement PS25/12, and it mandates daily reconciliation of safeguarded funds, with supervisory direction pointing squarely at “show me the position at any moment.” An estimate is not an answer to that question, and an interpolation is an estimate wearing a timestamp.
I would still make the trade, but the event log is not free, and that is the part most teams leave off the slide. It grows without bound. Every point-in-time query pays replay compute. Every downstream report that reads a snapshot table has to be rebuilt against the log. That is the real bill for being able to answer the 11:47am question, and most teams have not put it on the budget yet.
