This is still in Beta, but the directions to opt in are there:
Steam news update
The game is also 33 percent off to celebrate. Not sure if / when the updates are planned for other versions, though I imagine at the least the boss rush and easy mode will be.
Very impressed they did this, I had written it off as a pipe dream.
Edit: At the end of the article they suggest it will be coming to Mac, Linux and consoles later once they're confident in the stability. Right now this is only for Windows on Steam. DRM free versions like GoG will likely receive an update once the patch graduates from Beta.
Steam news update
*Note: There is a toggle in the options menu that allows you to switch between 60 and 30 fps in case it causes performance issues on your system. You can also revert back to the default branch.
This conversion was indeed a massive task to undertake: we worked through over 115 thousand lines of code the past several months in order to make this happen, manually changing timings of each object and enemy, fixing the dozens upon dozens of little problems that arose when changing frame timing, optimizing the game and testing the bits out of it internally.
Boss Rush + Newcomer
As no small aside, in addition to the frame rate boost, we have a Boss Rush mode with new achievements! It can be unlocked after you beat the game in the standard mode.
We also have a "Newcomer" mode for folks looking for a less intense challenge. It will have a limited set of achievements in it, so players will have to beat the game on the standard mode in order to get everything.
The game is also 33 percent off to celebrate. Not sure if / when the updates are planned for other versions, though I imagine at the least the boss rush and easy mode will be.
Very impressed they did this, I had written it off as a pipe dream.
Edit: At the end of the article they suggest it will be coming to Mac, Linux and consoles later once they're confident in the stability. Right now this is only for Windows on Steam. DRM free versions like GoG will likely receive an update once the patch graduates from Beta.