Andy Keene was in his third-floor room at the Canopy by Hilton Hotel when he heard a predawn commotion. He looked out expecting to see window cleaners, but was surprised to see a twisting bolt of shiny steel rising from the ground and going up and up, its curvy spire becoming thinner and thinner.

“It was very Jack in the Beanstalk,” said Keene, who is from Cincinnati and had unexpectedly become the first known public witness to what he soon figured out was this “beautiful sculpture.”

“Node,” a twisting and tapering tree branch that weighs 8 tons and rises to a point at 102 feet, had been installed in the quiet hours to become the tallest freestanding sculpture in San Francisco, with no fanfare around its installation in the public plaza at the entrance to the Yerba Buena/Moscone Station of the Central Subway, which opened in January.

All those expectant T line riders,who have yet to flock to the long-awaited subway,now have a station signpost that can be seen up and down Fourth Street.

“It’s amazingly tall,” said Kathy Mancall of Oakland who was standing on the sidewalk with Keene once the morning sun was up and shimmering. “You just have to keep looking and looking to find the top.”

The sculpture, by New York artist Roxy Paine, was funded by the city’s 2% Art Enrichment Ordinance. It requires a small slice of the budgets for major construction projects to be dedicated to either purchasing or commissioning public art. In this case the slice amounted to $1.45 million, with the artist selected from 154 applicants.

This is Paine’s first San Francisco commission, and he was not onsite for the installation. He did not respond Sunday to an email request for his own description of his sculpture. In his statement for the competition, he described his artwork as part of an “enormous bio-industrial rhizomatic organism,” and “an elegant line connecting earth to sky, people to underground systems and sculpture to city.”

Hard to state it more plainly than that.

Before settling on Paine’s design, the Arts Commission also considered purchasing an existing piece, “Tower” by Sol LeWitt for the location.

“Node” is 10 feet taller than“Venus,” another stainless steel figure,which is the courtyard centerpiece at the Trinity Apartments in the Mid-Market neighborhood and has enjoyed seven years as the city’s tallest sculpture.

Paine won the competition in 2013. There was plenty of time, given all the delays in getting the Central Subway built and opened. “Node’ has been ready and in storage for years, awaiting Sunday’s debut.

“It’s a way-finder and an amazing feat of fabrication,” said Dorka Keehn, former chair of the San Francisco Arts Commission’s visual arts committee, which selected Paine. “It’s going to be seen from everywhere.”

The artist did not make the trip west for the installation, which started at 1 a.m. Sunday with “Node” leaving a storage yard in Dogpatch. It had come from a fabrication plant in four pieces and was assembled two days ago. In its full form it was hoisted onto a flatbed truck and brought to its location in a slow procession that took three hours from Dogpatch and did not exceed 3 mph.

Once onsite, it went up fast. Installation started around 5 a.m., when Keene was awakened. By 9 a.m. it was bolted in place.

A passerby named Telos, who has lived in the neighborhood for 40 years, observed, “I’m glad it wasn’t here when the high winds blew through last month because, who knows?”

As with all commissioned public art in the city, a structural engineer had to verify its stability, taking wind and earthquakes into consideration.

The other obvious concern was lightning. Standing at the base, which is just under 6 feet in diameter, it is easy to envision a bolt hitting the tippy top, which is a half inch in diameter, and lighting up the art in a way that neither direct sunlight nor streetlight nor automobile headlights can accomplish. If it happens, the piece will act like a lightning rod, with a system at its base to disperse the energy underground, said Jackie von Treskow, senior program manager of public art for the city.

The concrete foundation runs 2 feet below the pavement. “Node” seems impossible to miss, though people still managed on Sunday morning.

“我没有注意到它。我在看我的电话,“一个dmitted Greg Hinrichsen, a visitor from New York trying to navigate Muni. Once it was pointed out to him, Hinrichsen described the piece as “the coronavirus mutated.”

A descriptive plaque will follow. But for now, “Node” is open to interpretation.

“It looks like smoke billowing in the air,’ said Peter Hughes, who lives in the neighborhood. Bernard Enrile called it “an earthquake fault line. Or is it, like, a tree branch?”

The crowd coming into the station on Sunday started to pick up with fans in their replica jerseys heading to Chase Center for the Warriors-Kings playoff game, but they were already locked into basketball and in too big a rush to stop for art.

Reach Sam Whiting: swhiting@sfchronicle.com