Jonathan Blow plans to open-source new game's engine

In December, Order of the Sinking Star was announced. Jonathan Blow's new game that's been a decade in the making. Understandably, the focus has been on the game and its insane amount of puzzles (apparently ~1400). But the engine itself is also planned to go open-source after release:

"...there’s a plan to release its custom engine for free as an open-source project shortly after the game ships."

Seems to have been flying under the radar. (Or alternatively I've been living under a rock.)

No information on the license of the engine yet. Fingers crossed for a permissive one. Either way, big news.