Twitter’s Threads Threat to Meta Turns on What’s Under the Hood

Twitter is threatening to sue Meta Platforms Inc. over its Threads app, raising the specter of costly trade secrets litigation in a sometimes-nebulous area of law.

Twitter’s owner X Corp. expressed concerns over “recent reports” regarding Meta’s new, Twitter-like app and its hiring of “dozens of former Twitter employees,” in a July 5 letter. Many of the employees retained Twitter devices and trade secrets, according to the letter, which alleged Meta “deliberately assigned” those employees to develop Threads “in a matter of months.”

The letter addressed to Meta CEO Mark Zuckerberg comes days after Meta launched Threads, a microblog ...