Check out @predictionindex’s latest weekly market forecast report for this round: Polymarket + Kalshi together account for approximately 75% of trading volume, with all other platforms combined under <$30B。

Two details not mentioned in the report are actually more critical for prediction market players：
Kalshi is catching up to and even surpassing Polymarket
DeFiRate’s latest week：Kalshi $2.9B（60%），Polymarket $2.0B（40%）。 The two sides are locked in a tug-of-war in the weekly data—last week Poly just overtook Kalshi, and this week it was pulled back again.
The U.S. market is even more extreme. BofA 4/9-10 report：Kalshi 89%，Polymarket 7%， 4%。 Compliance + KYC are Kalshi’s structural advantages, while Polymarket is an on-chain protocol; it is temporarily at a disadvantage in reaching U.S. retail investors, and won’t flip in the short term.
The phrase “duopoly” can easily make people think Poly is still the top player, but in reality, the U.S. market is basically dominated by Kalshi on its own.
“Other 25%” may hide even bigger alpha
The small platforms mentioned in the Week 15 report：Opinion / Limitless / Myriad / / Probable / / Chain）...

In essence, this is the window period between new prediction markets going live and competition becoming fully mature for players.
A typical data point：a certain on-chain wallet generates $99K PnL in 30 days, with a gross profit margin of about ~21% per trade. Compared with Polymarket’s mature order book depth of 0.5-2%, it’s more than 10 times higher.
Every new prediction market has such a 1-3 month window. Missing the first wave means missing most of the opportunities.
So the takeaway for players：watching the weekly tug-of-war between Polymarket+Kalshi is not the same as watching the entire track. The real misaligned alpha is in those new platforms that haven’t been fully played out yet—provided you monitor early and get in as soon as they launch.