Kobo turned down 45% of self-published books last year, largely due to issues related to AI.

      A self-publishing platform is intended to be welcoming. However, last year, Kobo dedicated a significant portion of its resources to rejecting submissions.

      In 2025, Rakuten Kobo declined 45% of the titles submitted to Kobo Writing Life, its self-publishing service. CEO Michael Tamblyn claims that over 80% of these rejections were due to books he deemed obviously AI-generated and of very low quality. According to him, hundreds of thousands of submissions were turned away.

      Tamblyn revealed these figures during a keynote address at the CONTEC conference in Buenos Aires in April, later reiterating them in a post on Threads in early May. He described the influx of machine-written manuscripts as a deluge that barely registered as an issue a few years ago but now fills the rejection pile.

      The statistics warrant careful consideration, and Tamblyn provided some clarity. The 45% represents the proportion of rejected submissions, not the percentage of those submissions that were AI-written; the 80%-plus figure refers only to the rejected titles. Kobo has not disclosed the overall number of files reviewed, the complete reasons for rejections, or the criteria used to determine if a manuscript is machine-generated.

      This assertion highlights the platform's approach more than it quantifies the actual prevalence of AI in self-publishing. That caution is important because detection remains a challenge. Tamblyn acknowledged that the AI-detection software Kobo uses often confuses human writing with machine-generated content and vice versa. Consequently, the company has chosen to focus on quality as the primary reason for rejection rather than trying to verify the exact origin of each submission.

      A manuscript that appears low-quality and mass-produced will be rejected, regardless of its source. This policy is outlined in Kobo’s guidelines. A help page updated in May details common rejection reasons, such as titles that are too short, contain AI-generated material, have poor translations, or are priced excessively. Kobo reserves the right to accept, decline, suspend, or remove any title, states that submitted works will not be used to train generative-AI systems, and retains the right to utilize AI to read and analyze texts for assessment purposes.

      This approach represents a more restrained version compared to how the rest of the industry is handling the situation. Amazon’s Kindle Direct Publishing has taken a different approach by requiring authors to disclose AI-generated text, images, or translations at the time of upload since September 2023, while not requiring a declaration for AI-assisted content. In contrast, Kobo prefers to reject submissions rather than mandate disclosures.

      Both platforms respond to the same challenge: the overwhelming influx of low-cost machine-generated text, a concern once considered theoretical but now faced on a large scale. What Kobo has not clarified is how many legitimate books were rejected in order to filter out the subpar ones. The burden of a market saturated with generative content is partially shouldered by those writers who find their works caught in the filtering process.