Can an AI agent beat Kalshi's Philadelphia high temperature market?

From a rule to a record

A backtest of a Philadelphia temperature rule tells you what it would have done against prices already known. This page wants the other thing: how the idea that the low's top bracket is overpriced the evening before fares against the KXLOWTPHIL book as it stands, each day at 8:00 PM Eastern, filled at the ask, charged Kalshi's fee (about 1.7¢ a contract at 45¢), and settled when the CLIPHL report says so. So the Philadelphia agent runs on Windmill like any user's agent, and each bet it places on KXLOWTPHIL is written here as it settles, wins and losses alike.

How the agent works

The agent is the rule below in plain English, on Claude Haiku 5.5, scheduled once a day, at 8:00 PM Eastern. It builds its record in four steps.

1. Read the ladder

Every day at 8:00 PM Eastern, it reads tomorrow's KXLOWTPHIL ladder (Philadelphia's daily low), bracket by bracket, with the live ask on each. A KXLOWTPHIL day in the facts below had 6 brackets, listed about 39 hours before the ladder closes at 1:00 AM Eastern time. It can also open the National Weather Service's forecast and the latest reading at Philadelphia International Airport from api.weather.gov, public pages its fetch tool reads.

2. Filter for the setup

It places nothing unless this holds:

• the top bracket ("X° or above") has a YES bid of 35–75¢

Why this setup: Philadelphia's daily low landed in its ladder's open-ended top bracket on 23 of the 67 days below; to win, that bracket needs the dawn and the next evening both to stay mild, so the rule bets NO on it the evening before.

3. Size and place

It buys 5 NO on it at the NO ask (100 − YES bid), on paper against the live KXLOWTPHIL book: a paper order fills only against what the book shows at that price. At about 45¢ a contract, Kalshi's taker fee at KXHIGHPHIL's settings (fee type "quadratic", multiplier 1) is about 1.7¢. So the five contracts cost about $2.34 all in, and pay $5.00 if they win.

4. Hold to settlement and record it

Every position is held until Kalshi settles the day on Philadelphia International Airport's official reading, the National Weather Service report CLIPHL as The Weather Company reports it, a median 6.2 hours after the ladder closes. The price paid, the fee, the result and the net go into the record below as each bet settles. Most of the daily runs end with no order, and the agent's log keeps those too.

The record: October 30, 2026

Started October 28, 2026; no settled bets yet.

Nothing is read into the record before thirty settled bets.

It runs this page's starter rule, word for word:

“Every day at 8:00 PM Eastern, on tomorrow's KXLOWTPHIL market (Philadelphia's daily low): if the top bracket ("X° or above") has a YES bid of 35–75¢, buy 5 NO on it at the NO ask (100 − YES bid). Otherwise no order. Hold to settlement.”

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The market the rule is betting into

Kalshi's API listed 67 settled Philadelphia days, from Aug 24, 2026 to Oct 29, 2026: 402 brackets, 6 a day in the median, of which 67 won. The official highs ran from 61°F (Sun, Oct 18) to 93°F (Tue, Sep 1), with a median of 77°F, and on 5 of the 67 days the winner was one of the two open-ended brackets at the ends of the ladder. A median day traded 37,664 contracts across its brackets over the last 7 days.

Each day's ladder was listed about 39 hours before it closed, closed at 1:00 AM Eastern time after the day it is about, and settled a median 6.2 hours after the close, once the official reading was in. Trading runs through the afternoon, while the high is still being set: a rule that buys late in the day knows more, and pays for it in the price.

Philadelphia's official highs

The ten newest days:

The daily low (KXLOWTPHIL)

Kalshi also lists Philadelphia's daily low as its own series, KXLOWTPHIL, on the same station. It settled 67 days from Sun, Aug 23 to Wed, Oct 28, with official lows from 39°F to 75°F. A low is often set in the early morning, so its ladder is a different question from the high's, on the same report.

How the 1 PM favorite did

For each of the 48 newest days up to Oct 29, 2026, we read Kalshi's quote 12 hours before the close and took the favorite, the bracket priced highest, at its ask. 47 had a quote at that moment, and the favorite won 31 of them. Breakeven is the price plus Kalshi's taker fee, as a share of the $1 a winning contract pays.

Three notes on that table. The 80–99¢ band has the widest gap between win rate and breakeven, 100% against 91.0%, and at 5 days its interval runs from 57% to 100%, which includes breakeven. The 40–59¢ favorite won 11 of 21 and still fell short of its 55.7% breakeven. And every band's interval includes breakeven, which is why the last column reads the same three times. In our read of Kalshi's prices, the Philadelphia favorite 12 hours before the close is priced about right. Nothing on this page says a buyer of the favorite has an edge.

The rule under test trades KXLOWTPHIL, not the KXHIGHPHIL ladder this table reads, so these rows are the high's baseline, not its own; its price, 25–65¢ a contract, is what "What success looks like" below works from.

Kalshi's rules, in Kalshi's words

This is the rule of the market that was open (KXHIGHPHIL-26OCT30-T78) when we read Kalshi's API on October 30, 2026, quoted from Kalshi; the series and its full rules are on Kalshi's site. The day and the bracket's bounds change with every market:

“If the maximum temperature recorded at Philadelphia (CLIPHL) for Oct 30, 2026, is greater than 78° fahrenheit according to The Weather Company, then the market resolves to Yes.”

Kalshi adds, in the same market's rules:

“Not all weather data is the same. While checking a source like AccuWeather or Google Weather may help guide your decision, the official and final value used to determine this market is the maximum/minimum temperature as reported by the Weather Company.”

The series names The Weather Company as its settlement source. Kalshi lists the series with the fee type "quadratic" at a multiplier of 1: a taker pays 1.8¢ a contract at 50¢ before rounding, less toward either end, and a resting order that fills later pays nothing. The fee calculator works out the fee and the breakeven for any price.

The rules name the station "Philadelphia (CLIPHL)": the daily climate report issued for Philadelphia by the National Weather Service's Mount Holly, New Jersey office, not the Philadelphia office one might expect. (NWS Mount Holly, climate report CLIPHL, checked October 28, 2026.)

What success looks like

A positive net per contract after Kalshi's fees over thirty settled bets, with the confidence interval clear of zero, would be a result.

A rule that only matches its price is not one. A contract bought near 45¢ that wins as often as that price says, 45 times in a hundred, loses about 1.7¢ a contract to the fee alone, so the line to beat on KXLOWTPHIL is a win rate of about 46.7%, not 45%. Each win at that price nets about 53.3¢ a contract after the fee and each loss costs 46.7¢, so one win covers 1.1 losses.

The rule runs once a day, so thirty settled bets take at least 30 days, and longer when the setup is rare. If the record climbs, the idea that the low's top bracket is overpriced the evening before holds at these prices. If it falls, the idea goes, and the record stays on this page.

Follow along

• This page refreshes every hour from Kalshi's settled data and the agent's own log.
• Copy the Philadelphia agent: the button below opens the builder with this KXLOWTPHIL rule, to run as written on paper under your own account, or with your own numbers in place of 25–65¢.
• The fee calculator shows the fee and the breakeven at any price on KXLOWTPHIL.
• The 90-strategy test is the longer version of this exercise: about 90 rules and 4,200 paper bets across ten days.
• The Kalshi markets hub lists the other weather cities and every other market page.

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Questions

What does Kalshi's Philadelphia high temperature market settle on?

On the day's maximum temperature at Philadelphia International Airport, as The Weather Company reports it; the rules name the station PHL report (CLIPHL). Exactly one bracket of the day's ladder wins.

What is the fee at 50¢?

A taker pays 1.8¢ a contract before rounding at 50¢ on this series (fee type "quadratic", multiplier 1), less toward either end. The fee calculator gives the fee and breakeven at any price.

Is a bot here profitable?

Nothing on this page says so. The favorite 12 hours before the close won 31 of 47 days in our read of Kalshi's prices, and the table shows each price band against its breakeven: 3 of its 3 bands are inside noise. Run your own rule on paper to see what it does, before you risk money.

Paper or live?

Agents trade on paper unless you build them live. Paper orders fill against Kalshi's live order book with Kalshi's fees and settle when the real market settles. To trade real money, connect your own Kalshi API key and build a live agent; your money stays on your Kalshi account.