You will be able to purchase it on Steam after Destiny 2 is released on Steam fully.
If you want it now, then no, there's now surefire way to purchase it for PC at this time because of it being removed from Blizzard's store.
English
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Oh man, I'm very impatient and can't wait for month. But thanks anyway.
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It's less than three weeks away, on October 1st or shortly thereafter.
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Will buying the Shadowkeep Deluxe edition activate Forsaken?
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No, as Forsaken is not included in either Shadowkeep package. You’ll have to wait for it to be offered as a stand-alone DLC on Steam, on Oct 1st.