Meta has settled a major lawsuit with dozens of US states over claims that its platforms harm children's mental health.

The deal, announced Wednesday, ends a trial in California and requires Meta to pay up to $18 billion.

It also includes new safety measures for young users on Instagram and Facebook.

The settlement involved four states as plaintiffs: California, Colorado, Kentucky, and New Jersey.

It also resolved a separate trial in Tennessee.

Tennessee Attorney General Jonathan Skrmetti said the deal provides "unprecedented protections" for kids and record-setting money for the state's Children's Digital Protection Fund.

Two states did not join the settlement.

New Mexico had already won its own case against Meta, with a judge ordering the company to pay $567 million in August.

Florida's attorney general said the settlement was not tough enough on Meta.

Separately, hundreds of US school districts have sued social media companies over costs related to children's mental health.

A Kentucky school district case settled before trial this summer.

In another first-of-its-kind case, a jury found Meta and YouTube liable for social media addiction and awarded $6 million in damages; both companies have appealed.