Security firm Calif.io demonstrated an untethered jailbreak on an iPhone 18 Pro running iOS 27.0.1 on stage at Hexacon, the offensive security conference held in Paris, on Friday. According to the company, it is the first time an untethered, permanent jailbreak has succeeded on devices of this kind, and root access returned even after the handset was rebooted.

A jailbreak strips away Apple’s software restrictions. “Untethered” means the modification comes back on its own after a restart, with no computer attached. By contrast, tethered or semi-tethered jailbreaks require reconnecting the device to a computer after each restart.

Apple builds the iPhone as a locked-down system, with signed code, a sandbox around every app, and a protected startup chain, so owners cannot change how iOS works or run software the company has not approved. A jailbreak breaks that lock and hands the user root access, which allows them to install apps Apple never authorized, add new features, customize the interface, and use the phone in ways Apple did not intend.

The practice has deep roots. In the early days of iOS, users with jailbroken phones could record video before Apple shipped that feature natively. They were also able to run Android on their iPhones, unlock carriers, and install themes. Today, a user with a jailbroken iPhone can install apps outside the App Store, browse the full file system, and delete preinstalled bloatware. Few people do this anymore, but every working jailbreak on current hardware shows that the defenses Apple invests heavily in can still be beaten.

Video from the stage, posted by jailbreak researcher Billy Ellis, shows the team rebooting the phone, unlocking it with the regular passcode, and opening an SSH session as root, the highest level of access on the device. The terminal output listed iOS 27.0.1 and an uptime of about two minutes.

At #hexacon - demos iOS 27.0.1 untethered jailbreak on iPhone 18 Pro pic.twitter.com/S54aRrzHFS

— Billy Ellis (@bellis1000) October 16, 2026

Hexacon runs October 16 and 17 in Paris, so the demo took place on the opening day of the conference. The event is aimed at researchers who find and exploit security flaws, and its talks typically cover bugs in widely used platforms such as phones and browsers.

Calif has not said which vulnerabilities it used, and no public tool exists. Its newsletter post from the conference lists four demos, including a Signal one-click and an iMessage demo, and says everything “will be released in due time.”

3/ Can your iPhone do this? pic.twitter.com/gT0Z781Tnl

— Calif (@calif_io) October 16, 2026

Getting root on a current iPhone usually takes a chain of bugs that escapes the app sandbox, takes over the kernel, and gets past hardware-backed defenses such as Pointer Authentication Codes, which detect tampering with memory pointers. A full chain of this kind is difficult to assemble, which is why successful public demos on current hardware are uncommon. Surviving a reboot is harder still, because Apple checks the code that runs at startup. That startup check is a large part of why untethered jailbreaks, once the norm in iOS’s early years, have been rare on modern hardware.

Artificial intelligence tools have featured in Calif’s earlier research. In April, Calif’s Thai Duong wrote that Claude helped him take apart an iOS Safari exploit, in a series on how a real iPhone jailbreak works. In May, Calif said that Anthropic’s Claude Mythos Preview helped it build a macOS kernel exploit against Apple’s M5 chip protections in under a week.

“We didn’t build the chain alone. Mythos Preview helped identify the bugs and assisted throughout exploit development,” he said.

Apple’s iOS 27 security notes, published September 14, credit Calif.io “in collaboration with Claude and Anthropic Research” for two bugs that let an app cause a denial of service or a system crash. Nothing in the notes ties either bug to the jailbreak.

A chain that gives root on a fully updated iPhone is the same kind of capability that commercial spyware vendors sell to governments, and Apple usually patches such chains once it learns the details. How long iOS 27.01 stays exposed therefore depends largely on when Calif chooses to publish. Until the details are published and patched, the exploit chain demonstrated on stage remains effective against devices running iOS 27.0.1.

Apple has not publicly commented on the demo as of Friday, and says it does not confirm security issues until patches are available. Calif has not said when it will publish the details. The next markers to watch are whether the newsletter’s promised releases, including the Signal and iMessage demos, materialize, and whether a future iOS update carries a fix once the details surface.