850k US physical + 150k UK physical + 350k RoW physical (Using VGCs distribution of past Halo games' sales)
Add in 1.05 million digital (MS said that it was the highest selling title first week on the Xbox store ever, previous record holder was Minecraft with 1 million first week) And when you consider that all special editions and bundles came with a digital copy, it's possible. However if NPD and chart track (for UK) tracked the special and limited editions since they are physical, they just come with a digital download code, thenthat would mean that some of these physical numbers would also be included in that 1.05 million digital, so maybe subtract 75k if that'sthe case.
That leaves us with 2.25 million first week (including digital).
