3DS new firmwire: 2.1.0.4U/E

Form the Nintendo USA site.

Version 2.1.0-4U includes the following improvements:System stability improvements and other adjustments:Further improvements to overall system stability and other minor adjustments have been made to enhance the user experience.
Your Nintendo 3DS system and software are not designed for use with any unauthorized device and/or any unauthorized software. Please note that the Nintendo warranties do not cover any defects to or defects caused by unauthorized devices, software, modifications and/or non-licensed accessories. Furthermore such use may lead to injury to yourself or others and may cause performance issues and/or damage to your Nintendo 3DS system and related services. Nintendo (as well as Nintendo licensees or distributors) is not responsible for any damage or loss caused by the use of such devices, software, modifications or non-licensed accessories. IMPORTANT: After the Nintendo 3DS system is updated, any existing or future unauthorized technical modification of the hardware or software of your Nintendo 3DS system, or the use of an unauthorized device in connection with your system, may render the system permanently unplayable. Content deriving from the unauthorized modification of the hardware or software of your Nintendo 3DS system may be removed. Failure to accept the update may render games unplayable.I definitely won't be updating for now.

Still working are Ez-Flash Vi (All I know)Not working: ??

acekard 2i works too, i believe in gbatemp they mentioned that this update wasnt blocking any flashcarts at all

Yes, iluvfupaburgers is correct, The new 3DS firmware 2.1.0-4 didn;t block any flashcard, it has been confirmed that Acekard 2i, DSTWo and R4i gold 3DS are stilll working on it without update. I think other other cards also work well.

I guess no flashcard were blocked at all...my supercard dstwo works just well :D

I tried my flashcards-Acekard 2i 4i SDHC 3DS R4i GOLD 3ds, they all works well with the new firmware. It seems will not bloack any flashcard.

They aren't gonna block flashcards for normal DS games. I guess they're just setting up an AP for the 3DS in the (rare) case flashcards for the 3DS are coming. I hope they will succeed because I will not be using flashcards for the 3DS.

m3 zero also works!