New Delhi, Aug. 2 -- WASHINGTON - When President Donald Trump posted to Truth Social on Saturday morning that he was calling off the planned strikes against Iran and opening a path to negotiations, someone was reading it before you were. Milliseconds earlier, perhaps a few seconds. In the era of algorithmic trading, that gap is the difference between a position that moved on news and one that moved on public knowledge.

That gap is now a product. Trump Media and Technology Group went live Saturday with Truth API, a subscription service that gives financial firms and institutions real-time alerts on Trump's posts before they appear in the public feed. TMTG has not publicly disclosed its pricing structure, though the service was marketed to...