GPT-5.6 helped break Chrome’s defenses for a $250,000 Google bounty.

Xbow engineer Brendan Dolan-Gavitt ran OpenAI’s gpt-5.6-sol, against the browser’s source code over six days and $40,000 of compute

The agents searched code, tested hypotheses, and drafted the exploit stages, while Dolan-Gavitt and colleagues picked targets, supplied context, and decided which pieces to join.

Reconstructing the Codex logs, Xbow put the compute bill at roughly $40,000, a fraction of the prize, and well below the months of specialist labor such work once demanded.

The finished chain turned ordinary JavaScript in a Chrome tab into code running outside every sandbox, crossing two protective boundaries through three separate flaws.
Google reproduced the chain, confirmed all three bugs, shipped fixes, and awarded the first $250,000 full-chain Chrome reward under rules it set