Here’s the language suggested by the Authors Guild to be included on the title page of your work as a Notice to the AI companies that they are prohibiting from harvesting your work or generating material therefrom.

No Generative AI Training Use.

For avoidance of doubt, Author reserves the rights, and [Publisher/Platform] has no rights to, reproduce and/or otherwise use the Work in any manner for purposes of training artificial intelligence technologies to generate text, including without limitation, technologies that are capable of generating works in the same style or genre as the Work, unless [Publisher/Platform] obtains Author’s specific and express permission to do so. Nor does [Publisher/Platform] have the right to sublicense others to reproduce and/or otherwise use the Work in any manner for purposes of training artificial intelligence technologies to generate text without Author’s specific and express permission.