To me, there is a slight difference in nuance. "in future" tends to mean "on all future occasions, starting from now", while "in the future" tends to mean "one one or more specific future occasions". In this sentence I personally would have said "in the future", but different speakers may vary in their usage.
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Mr WordyContrast "I'm going to work harder in future", which means I'll start doing that as a regular habit.If I've understood completely, I believe his working harder starts from now onwards and happens on a regular basis.
AnonymousIf I've understood completely, I believe his working harder starts from now onwards and happens on a regular basis.Yes, that's right.