Spines, a startup that deploys AI agents to edit manuscripts, design book covers, translate text, market finished titles, and manage authors' social media campaigns, has secured $64 million in new capital, the company said Monday.

The company, which maintains offices in Israel and New York, operates as what is known as a "hybrid publisher." Hybrid publishers largely serve authors who are unable to land a traditional deal with a commercial publishing house, or who wish to retain more control and receive a larger royalty split than a conventional publisher typically offers. As with self-publishing, authors pay an upfront fee to release their book, and the publisher also takes a share of sales as royalties. The distinction is that hybrid publishers provide a greater level of service and support than self-publishing platforms. On the self-publishing end, free do-it-yourself platforms such as Amazon's Kindle Direct Publishing leave production, design, and marketing work in the author's hands — the gap that service-oriented hybrids like Spines step into.

The funding package consists of two components: a $29 million Series A-1 equity round led by Zeev Ventures, with participation from Aleph, NordStar, M-Fund, LionTree, and angel investor Dan Senor, plus $35 million in what the company calls "a non-dilutive growth financing facility" — a debt arrangement that supplies capital without requiring Spines to sell shares — from Twelve, a credit-focused investment management firm. Spines declined to disclose its valuation following the raise.

Alongside the funding announcement, Spines said its new AI-powered services have pushed the company to a $50 million annual revenue run rate, representing 400% year-over-year growth. Founder and CEO Yehuda Niv told Fortune that the company has published more than 8,000 authors to date, accounting for some 12,000 titles, and that roughly 400 new writers sign up for the service each month.

Niv's path into publishing began about 15 years ago, when, partway through a master's degree in electronic engineering, he released a book of his own and concluded that "the publishing process is completely broken." That frustrating experience motivated him to enter the industry himself. He bootstrapped Niv Publishing, which he says grew into Israel's largest publishing house, releasing about 1,200 titles a year. Roughly six years ago, he said, he realized that AI would eventually "make every [traditional] publishing company on the planet irrelevant." In response, he founded Spines in 2021. The company describes itself as an "operating system for authors."

Through the platform, writers upload a finished manuscript, and specialized agents handle editing, proofreading, formatting, cover design, metadata, ebook and print-on-demand files, and distribution to more than 100 channels, including Amazon, Barnes & Noble, and Baker & Taylor. Authors can produce an audiobook with a synthetic narrator or a clone of their own voice, and translate the book—and that audiobook—into other languages. Spines currently offers seven target languages and plans to reach 20 within six months. Once a title is published, the platform tracks royalties and runs marketing campaigns.

Niv argues the agents can handle some tasks better than the freelancers authors typically hire. Of the roughly 10,000 authors he published in Israel, he said, every single one had the same complaint: "The cover designer didn't have time to read my book." Spines' cover agent reads the manuscript, researches which retail categories give the book its best shot, identifies which designs perform best in those categories, and creates a cover matched to those metrics.

The agents also dramatically shorten the journey from manuscript to bookstore shelves—a process that takes anywhere from many months to more than a year in traditional publishing—bringing it down to just weeks.

Spines' publishing packages start at about $3,000 and climb to $20,000 for a premium tier that releases a book in three languages, each with an audiobook; most authors choose a mid-tier bundle costing between $5,000 and $7,000, Niv said. The company recently changed its royalty split so authors keep 80% of net royalties, up from 70%. Spines reports royalties monthly, rather than the twice-yearly or annual statements common across the industry, and is working toward weekly and eventually real-time reporting.

Niv said Spines publishes only books "100% written by humans" and uses software to screen out AI-generated manuscripts. That safeguard has taken on added weight as generative-AI tools make it easier to mass-produce text. "We are not here to replace [authors] with AI," he said, insisting that the company exists to "empower" human writers.

Still, some aspects of Spines' use of AI may raise copyright questions, particularly around AI-designed book covers. U.S. courts and the Copyright Office have held that images made entirely by AI cannot be copyrighted. Without copyright protection, such images fall into the public domain, where anyone is free to copy or reuse them. Niv said Spines licenses the image-generation tools it uses and passes that license on to authors. He argued that this is often a broader license than authors receive from human illustrators, who usually keep the copyright and license the image only for the book cover.

Spines employs roughly 350 people, Niv said, only about 50 of whom work in R&D; most of the rest handle customer success and support, guiding authors through decisions he says software cannot make for them. "Our AI agent designed for you three amazing covers, but eventually you have to choose one," he said. "For an author, that's an emotional decision." Spines' human marketing experts are on hand to help.

For now, Spines sells its platform directly to authors who lack a traditional publisher. But Niv said the company is in early talks with one of the Big Five U.S. publishers about a partnership in which Spines and its AI agents would be used to help run that publishing house's services.

"Spines has all the ingredients to become the category leader in the next generation of publishing," Oren Zeev, the founding partner of Zeev Ventures, said in a statement.

Niv said Spines will use the debt facility to fund growth and the equity to build out its product and expand beyond the U.S. into other English-speaking markets, including the U.K., Canada, and Australia. He said he is aiming for 200% to 300% annual growth. Most of the company's staff work in Eastern Europe, the U.S., and Latin America, but R&D and management are based in Herzliya, Israel. How quickly Spines reaches its 20-language target, and whether the early talks with a Big Five publisher mature into a formal deal, are the concrete markers to watch as that next phase unfolds.

This story was originally featured on Fortune.com.