It’s in this article:

Under the terms of the agreement, “AI can’t write or rewrite literary material, and AI-generated material will not be considered source material” under the contract, meaning that AI-generated material can’t be used to undermine a writer’s credit or separated rights.

The summary notes: “A writer can choose to use AI when performing writing services, if the company consents and provided that the writer follows applicable company policies, but the company can’t require the writer to use AI software (e.g., ChatGPT) when performing writing services.”

The company also must disclose to the writer if any materials given to the writer have been generated by AI or incorporate AI-generated material, and the WGA says that it “reserves the right to assert that exploitation of writers’ material to train AI is prohibited by MBA or other law.”