The short announcement from Microsoft's Xbox developer relations team makes it clear that this price increase goes into effect immediately. I understand it's not just impacting US developers, as the price of these development kits is also going up across Europe and elsewhere. That's likely because those "macroeconomic" conditions extend beyond just US tariffs, with currency fluctuations, production costs, and other elements impacting pricing.
Microsoft's Xbox dev kit was already expensive because it comes with additional hardware on the inside and out, to let developers build and test Xbox games for both the Xbox Series X and Xbox Series S consoles. Microsoft has equipped its latest dev kit with 40GB of GDDR6 memory, instead of the 16GB found on the Xbox Series X console. It also has a more compute units enabled, the all-important debugging tools onboard for testing games, and three USB ports at the front. Microsoft also equips its Xbox dev kits with a front panel display and five programmable buttons.