After three years, Call of Duty is bringing back campaign early access with Modern Warfare 4

Activision has announced that Modern Warfare 4 will make its single-player campaign available to play up to one week prior to the full game's launch date. This makes the Korean Peninsula-set campaign accessible as early as 16th October for some players - that's a full week before the official release on 23rd October.

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source https://www.eurogamer.net/call-of-duty-modern-warfare-4-campaign-early-access