By law, Siam Gin is the first officially registered Thai gin. You may have seen Iron Balls or Saneha by the Chalong Bay people, but if you look closely at the bottle, nowhere says “gin,” just “white spirit,” as they are distilled at a “community license” distillery.
The reason Siam Gin can register as an official “gin” is because it was distilled at a properly complete distillery in Kanchanaburi, CCM, which holds a different license to products in the past. 
The difference in distillery licenses includes the level of tax, how much you are allowed to make each year, and various alcohol options for the distillery. At CCM, they are even allowed to make whiskey with completely legal aging. The plan is to try and elevate more local spirits.
Apart from the juniper that needs to be imported, Siam Gin is made from 100% Thai botanical ingredients. You’ll find additions like jasmine rice, pomelo peel, lemongrass, kaffir lime leaves, and ginger, to name a few, and it has a 45% alcohol by volume.  
Priced B980 a bottle, the gin is not yet available for retail but can be found at a few Bangkok cocktail bars. The brand can be contacted for queries at @majesticbar.