The BLS's August 2026 CPI report landed at 8:30am ET (12:30 UTC) on Friday, September 11 - core inflation a tenth of a point hotter than forecast - and Polymarket's "Fed Decision in September?" market repriced within the hour. "Will there be no change in Fed interest rates after the September 2026 meeting?" fell from 41.5c to a 16.5c low, settling near 19.5c, while "Will the Fed increase interest rates by 25 bps?" rose from 57.5c to an 81.5c high, settling near 78.5c. Numbers below are from Gamma and the CLOB, fetched 2026-09-12 11:00 UTC.
01The reportCore inflation ran hot, and it was the last read before the meeting
The consumer price index rose a seasonally adjusted 0.4% in August, putting the annual headline rate at 3.4% - in line with estimates and driven largely by gasoline, which jumped 3.9% for the month (up 27.4% year over year) after falling 2.9% in July. Core CPI, which strips out food and energy, rose 0.3% for the month - a tenth of a point above forecast - holding the annual core rate at 2.4%. It was the last inflation print the Fed would see before the September 15-16 FOMC meeting, where the rate decision lands at 2pm ET September 16.
This blog covered the same market a week earlier, on September 4, when Fed Governor Christopher Waller said he could support holding rates steady "if this continues in the data due over the next two weeks" - conditional language pointing straight at this report. At the time, "no change" was the 59.5c favorite. It had drifted since, down to 41.5c by the morning of September 11, before the CPI print itself did the rest of the work: the data Waller was waiting on came in hotter than he needed, and the market repriced accordingly.
02The chartA 16-point gap becomes a 61-point gap in half an hour
Both contracts sat flat through most of Thursday and into Friday morning - "no change" drifting between 36.5c and 41.5c, "hike 25bps" between 57.5c and 60.5c, a market waiting on one number. At 12:30 UTC, the minute the CPI report crossed the wire, "no change" broke: 40.5c to 29.5c within ten minutes, 18.5c by 13:00, a 16.5c intraday low by 15:10. "Hike 25bps" moved the mirror image, from 57.5c to an 81.5c high over the same stretch. Both have settled within a couple points of those extremes since - near 19.5c and 78.5c respectively - a level shift, not a spike that faded.
03What's priced nowA two-way race, with the tails priced to nothing
FED DECISION, SEPTEMBER YES 24H
No change 19c -19pt
Increase 25 bps 78c +18pt
Decrease 25 bps 0.3c -0.2pt
Increase 50+ bps 0.7c -0.1pt
Decrease 50+ bps 0.1c -0.1pt
The order books on the two live legs are both a tight 1c wide: the "increase 25 bps" contract has 179,680 shares bid at 78c against 166,576 offered at 79c, and "no change" has 195,097 bid at 19c against 60,672 offered at 20c - real size resting on both sides of a market that just moved 20 points in an hour, not a stale quote nobody has touched. The other three legs - a 25bp or 50bp+ cut, and a 50bp+ hike - are all priced under a cent; the market has effectively reduced the September decision to two outcomes and is pricing a hike as roughly four-to-one favorite over a hold. The event traded $20M over the prior 24 hours on $10.3M of liquidity, one of the most active markets on Polymarket right now. The FOMC meets September 15-16, with the rate decision due 2pm ET (18:00 UTC) on the 16th - four days out from this repricing.
04Watching the decision liveThe next move lands at 2pm ET on the 16th
A move like Friday's - a scheduled data release, a fast repricing, then a new plateau - is exactly the kind of window polymarket-tui is built to sit open through: the order book and price chart share one screen, so a 1c-wide book going from 40c to 18c shows up as it happens rather than as a headline afterward. The FOMC decision itself, four days from this print, will be the next test of whether the market's read on this CPI report holds.
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$ polymarket-tui
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