The Metropolitan Transportation Authority is preparing to roll out prototypes of new turnstile designs that are harder to jump over or sneak under as it seeks to crack down on fare-beating, which costs the agency an estimated $500 million annually.

At least two demonstration models have been installed in the famed Vanderbilt Hall at Grand Central Terminal — devices the agency has attempted to shield from public view by erecting a curtain that effectively walls off half the massive space from commuters passing through.

The curtain was tightly guarded on Monday by roughly a dozen MTA staffers — including spokesmen, police officers and other employees — all of whom made a concerted effort to keep reporters, photographers and transit buffs from gleaning glimpses of the devices through cracks in the sheets of fabric before the still yet-to-be-scheduled unveiling.

An MTA spokesman refused all requests for comment on Monday.

A Post reporter was able to make out the tale-tell signs of at least two models through the MTA’s blockade.

The word of the coming overhaul first leaked late Sunday night when a Reddit user posted a photo of one of the new demo models in Grand Central — the train hub’s historic chandeliers could be seen in a reflection captured in the image.

It includes large doors that swing open and stretch several feet high, making them much more difficult to jump over.

The model is said to be nearly identical to the fare gates recently bought by the national French railroad and installed at one of its key transit hubs in Paris, which are manufactured by the same firm, Conduent Transport Solutions.

French officials say the design can handle more than 30 people per minute, and they hope it will cut fare evasion in half.

Conduent’s gates have already caught the eye of Philadelphia’s transit agency, which announced earlier this year it was spending nearly $1 million to install them in two metro stations as part of a pilot project to try and reduce fare-beating.

A spokesman for the company did not respond to a request for comment.

Meanwhile, the second model spotted through the curtain by The Post reporter includes the large green arrows used by the new fare gates recently installed in Boston’s commuter railroad stations, which are similar to the system used by the London Underground.