Verdict: Mostly False. The central claim is contradicted because the latest supplied forecast gave Amy Acton a 21.6% chance of winning and Vivek Ramaswamy a 78.4% chance.
Republican Vivek Ramaswamy is predicted to lose the Ohio gubernatorial election to Democrat Amy Acton.
The Claim
Republican Vivek Ramaswamy is predicted to lose the Ohio gubernatorial election to Democrat Amy Acton.

Vivek Ramaswamy's chances of losing in Ohio as race shifted to "toss up"
Source: newsweek.com
Key Evidence
An April 10 prediction market modestly favored a Democratic victory, pricing it at roughly 55%, compared with about 44% for Republicans.
By August 11, the supplied forecast instead favored a Republican victory, with odds of 78.4% for Ramaswamy and 21.6% for Acton.
What the Evidence Shows
What is established
On July 10, the Cook Political Report classified the race as a toss-up rather than forecasting a definite Acton victory.
Both named candidates advanced as their parties’ nominees, establishing the general-election matchup but not its outcome.
Context and caveats
Forecast assessments changed over time: an April prediction market favored a Democratic win, the July classification was a toss-up, and the August 11 forecast favored a Republican win.
The claim does not specify which prediction or forecast it refers to, so earlier evidence can support the possibility that some prediction favored Acton, but it does not establish that this was the prevailing forecast on August 12.
The supplied evidence contains changing forecasts and does not identify the prediction referenced by the claim.