Updated September 1, 2026
September is shaping up to be a busy month for prediction markets.
The Federal Reserve has a closely watched interest-rate decision ahead, the US Open reaches its conclusion, Anthropic could move closer to one of the biggest technology IPOs in years, and renewed diplomatic activity could shift expectations around the Russia-Ukraine war.
Polymarket traders are already putting probabilities on all of them.
Here are five Polymarket markets worth watching throughout September 2026.
This could be the biggest prediction market of the month.
More than $74 million has already been traded on Polymarket's September Fed decision market, and traders currently give a 25-basis-point increase a narrow edge over the Federal Reserve holding rates steady.
The decision comes at the Federal Open Market Committee's September 15-16 meeting. The Federal Reserve's official calendar confirms that a policy statement and press conference are scheduled for September 16.
That gives traders two weeks to digest incoming economic data and comments from Fed officials.
It also makes this a particularly interesting market to monitor rather than simply check on decision day. A surprisingly strong inflation reading, weak employment report or change in Fed rhetoric could quickly shift the 56%-43% split.
What to watch: Inflation data, employment numbers and Fed commentary ahead of September 16.
Anthropic's potential IPO has quickly become one of Polymarket's most interesting technology markets.
More than $2.1 million had been traded across the market before we entered September.
That makes September important even if the IPO itself does not happen this month.
Reuters reported on August 27 that Anthropic was preparing to publicly unveil its IPO prospectus after Labor Day, with a possible stock-market debut in late September or early October.
A prospectus filing, confirmed listing date or delay could therefore send the Polymarket probabilities moving sharply.
What to watch: Anthropic's public prospectus and any confirmed IPO date.
This is one of the month's more consequential geopolitical markets.
Importantly, the market does not require a peace agreement. It requires an in-person diplomatic meeting aimed at a ceasefire, peace agreement or other substantive de-escalation.
There is at least a potential September catalyst. Ukrainian officials said in late August that talks involving Russian and Ukrainian representatives could take place during September, potentially with U.S. participation.
The situation remains extremely fluid, however. Russia intensified air attacks on Kyiv entering September, while fundamental disagreements over territory and security guarantees remain unresolved.
That combination of possible diplomacy and continued fighting makes the market one to monitor closely.
What to watch: Announcements of U.S.-mediated negotiations or an official Russia-Ukraine meeting.
Sports markets can move faster than almost anything else on Polymarket, and the US Open provides a perfect September example.
Nearly $15 million has already been traded on the men's winner market. Carlos Alcaraz currently leads at around 34%, followed by Alexander Zverev at 24%, with Taylor Fritz and Ben Shelton among the next group of contenders.
Those probabilities will change after virtually every significant match.
The tournament culminates with the women's final on September 12 and men's final on September 13 at Arthur Ashe Stadium.
Unlike a long-term political or economic market, tennis markets will effectively be repriced in real time as players advance or are eliminated.
What to watch: Alcaraz and Zverev's paths through the draw—and whether one of the American contenders can make a deep run.
Current Polymarket favorites:
The Ballon d'Or will not actually be awarded until October 26, but September could still be one of the most important months for this soccer market.
The official Ballon d'Or website says the announcement of the 2026 nominees is imminent, while UEFA has confirmed that the ceremony will take place in London on October 26.
That shortlist should provide one of the final major information events before voting and the ceremony.
Kane currently has a substantial lead, but the size of the market means even relatively small changes in sentiment could create noticeable movements.
What to watch: The official nominee announcement and any indications about how voters are viewing Kane's case compared with Yamal, Mbappé and Rodri.
These five markets also show how broad prediction markets have become.
In the same month, traders are putting probabilities on monetary policy, an AI IPO, international diplomacy, a Grand Slam tennis tournament and football's biggest individual award.
The most interesting market may be the Fed decision, where more than $74 million has already been traded and neither of the two main outcomes is close to certain.
But some of the biggest movements could come elsewhere. Anthropic's first public IPO filing, confirmation of Russia-Ukraine negotiations or one upset at the US Open could change a market within hours.
That is ultimately what makes September worth watching: the probabilities we see on September 1 are unlikely to look the same by September 30.
