Using the numbers we have available

UK attach rate was ~8.5%

US attach rate was ~10.5%

Japan attach rate was ~10%

If we use 10% as the average WW rate.. And use VGC's HW numbers:

15.1Mx0.10= 1.51M

Best case scenario for adding digital and bundles copies raises it up to "exactly" 2M (~300k digital and ~200k bundles)

Allow a small margin of error due to relying on VGC's HW totals.

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).