Faster US Stock Settlement Has Currency-Market Anchor Scrambling

CLS, the world’s largest foreign-exchange settlement firm, is racing to figure out a way to get the $7.5 trillion-a-day currency market ready for a huge change to trading in US stocks.

The US is less than four months from introducing what’s known as T+1, when it will halve the time it takes to complete equity transactions to just one day. The move will leave the world of foreign exchange — where trades typically take two days to complete — out of step.

Overseas investors buying US assets will need to secure dollars faster to complete deals, creating a desperate ...