Kings Island to announce ‘major new addition’ at 10 p.m. | LIVE coverage here

The new attraction will be touted 10 p.m. Thursday at an open-to-all-guests event that will see the park extend its Coney Mall hours from 8 to 10 p.m.

Kings Island officials won’t divulge what the announcement will concern, but our media partner WCPO has surmised that based on blueprints filed with the City of Mason, and construction already underway in the park, fans are fairly certain it will be a major roller coaster.

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The blueprints appear to show a 300-foot tall coaster on the site of the former Firehawk ride, one that dwarfs the iconic wooden coaster The Racer next to it.

It is called only “Project X” in the plans, according to WCPO.

The first set of plans showed only the foundation, but these show the actual coaster.

It would load at the old Firehawk entrance (in what is called X-Base), then climb a lift hill, and then take what appears to be a 305-foot drop according to coaster experts analyzing the drawing on KI Central Forums (it would have to surpass 300 feet to be considered a giga).

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The blueprints show it heading east past the Racer’s turnaround, toward the Kings Island and Miami Valley railroad.

It would then make a banked turn in what coaster fans call a “treble clef,” and would return to the loading base.

But the thrills would not end there: the plans show a helix, or corkscrew turn, near the end, before the final brake run.

And some dashed lines on the blueprint after the final turn suggest it may go through a tunnel before coming to a stop, according to the forums.

The park has been teasing coaster enthusiasts for several weeks by putting up posters on the fence in front of the secret construction zone, WCPO reported.

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Each day a new poster would go up, but with no explanation of why. Fans would rush to the fence as soon as the park opened at 10 a.m. to see that day’s new teaser.

Each poster shows a current or former ride at the park,. Once the posters were up, the letters on each spelled out the first letters of the R.E.M. song “The End of the World as We Know It.”

If the new ride is a “giga” coaster, meaning a coaster over 300 feet tall, it will be only the sixth giga coaster in the entire world. Ohio has one other giga coaster, Millenium Force, at Cedar Point in Sandusky, Kings Island’s sister park.

International theme park consultant, and Kings Island co-founder Dennis Speigel, told us the manufacturer is Switzerland’s Bolliger and Mabillard, which built the Diamondback coaster a decade ago. He said the track is already being built nearby at Clermont Steel Fabricators in Batavia.

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Kings Island and parent company Cedar Fair have yet to confirm any new ride. Asked Tuesday if the ride was a new giga coaster, park spokesman Chad Showalter said “the only way to know for sure what Kings Island is announcing on August 15th is to come and hear the official details firsthand.”

But Cedar Fair recently filed federal trademark names for rides called Orion and Polaris, indicating that Project X could soon be unveiled under one of those names, according to WCPO.