I see nothing in the features to suggest that it is.
Seriously, if you need more than nearly 4GB ram to publish something you're beyond doing something wrong. The speed increases of 64bit will help marginally at best.
Remember that's just the IDE. The flash player itself has been 64bit friendly for quite a while. What you see when you export into a flash player will run at full 64bit speed so if you do a lot of 3d you can rest assured you will see it full speed. The IDE itself? Doesn't really benefit from 64bit. It's not like After Effects or responsible for holding huge amounts of data.
How would it help? The vast majority of all apps on Windows are still 32bit.
Do you know why you think it'd perform better being 64bit? An argument could be made that compiling can happen more efficiently as pipelines don't need to double down to handle 64bit floating point precision but on a modern processor we're talking a couple seconds (billions of operations) extra. Is that worth recoding it completely for 64bit? Not really.
Exporting is different based on what is exporting as well. When you convert to ARM you use a different compiler which I assure you is utilizing 64bit. Also the perks of any modern i* intel processor with overclocking as it's very thread friendly.
You don't really need the Flash IDE to be 64bit. It won't make any noticable difference you yourself will detect. It will also require them making sure their plugins and extensions support 64bit so a rewrite of those is necessary too. It's just not worth it.
Video editing/encoding/transcoding/decoding? Hell yes. Flash player playback especially with Stage3D or a native API? hell yes. Flash IDE? Moot.
I'm just talking from experience. The program itself runs out of memory sometimes when I have other applications open that I am using with it.
So to answer my question, sinious thinks CS6 Flash Pro is not 64 bit.
Having seen release notes since Flash didn't even have a scripting language (good ole macromedia days) and every Adobe product launch since... forever... They usually say when something is now 64bit. They exclaim it from the roofs. Several OSX people here were so happy with the 64bit version of After Effects, Premiere, etc were recoded for their OS so they could use more than 4GB memory that's all you saw on the front page as a main feature. 64bit support to finally tap into memory past the ~4ish GB mark.
How much RAM do you have? I have 32GB ram on this machine, 16GB on a second dev box and a whopping 4GB on my laptop. On my 32gb station I don't care about open apps. On the 16GB station, ESPECIALLY when working on HD video, I keep almost no apps open. On the 4GB box I rarely have more than a few text editors, browsers, flash and photoshop open. Perhaps resource management is just the issue as I've NEVER seen flash run out of ram.
A better question is, which I actually don't know the answer to, is if flash is allowed to use system paging.
Anyhow I've seen a lot of people lately coming out that they can't open a 700MB FLA and 2 things come to mind. 1) WTF are you doing with a 700MB FLA? 2) Your physical memory is low or flash is corrupt.
I'm not saying I haven't had one gigantic 794MB FLA before. We all have our demons. But I didn't get any memory warnings. Probably because it was full of PNGs.
Here's something to keep in mind. Compression. If you use a lot of compressed video and images flash needs to "decompress" them to use them when they are needed which takes up a lot more than the FLA file sizes footprint. You could be hitting an issue like that.
What size of a FLA are you talking about?