Loopaza confirmed it in their rundown of upcoming Takara releases in May and August which show which also show which toys from the Siege line will come out in that time. The prices are all MSRP.

We also have domestice preorders up for those who can't wait for this new Prime. Both BBTS and TFSource have this toy priced at $449.99:
BBTS: https://www.bigbadtoystore.com/Product/ ... ails/84183
TFSource: https://tfsource.com/masterpiece/mp-44- ... mus-prime/
While the price is the highest we have ever seen, this toy does come with more accessories than all the recently high priced Masterpiece releases, one of which is a trailer.
Aside from the trailer, here is the list of accessories the toy is said to come with according to a post on Weibo. Since this is translated from chinese, there may be some parts lost in translation, the words in parenthese are a possible interpretation.
box, content:
- main body X1 (Optimus Prime)
- compartment X1 (trailer)
- cabin anti-aircraft gun X1
- small ball X1 (Roller)
- energy axe X1
- beam special effects X2
- laser rifle X1
- energy treasure X1 (the matrix)
- energy supply tube X1 (fuel hose for Roller)
- Spike X1
- Carly X1
- Spike Pula X1 (Sparkplug)
- Rocket Backpack X1 (Jet pack)
- Starscream Head X1 (to re-enact when Starscream is dressed up as Prime)
- Starscream Wings Accessories X1 (most probably the shoulder pylons to re-enact when Starscream is dressed up as Prime)
- An Unknown Item X1
- Replacement Head Carving X1 (Different face)
- War Damage Head X1
- Battle Damage Chest Parts X1
- character card X1