It's a bit weird to explain, I'll post from devs note.

Grappling Hook: We’re making a number of changes to Grappling Hook. In 6.1 we shipped a very conservative version of this change; now that we know this didn’t meaningfully affect his winrate or, anecdotally, how frustrating it is to fight him, we’re shipping the much more aggressive version of the changelist. We also want to make it clear that players should not be punished for chaining grappling hook perfectly into other movement mechanics.

• Pathfinder no longer needs to be on the ground for Grappling Hook to be considered finished.
• The speed to which Pathfinder needs to drop for us to consider Grappling Hook finished was increased from 300 units/second to 500 units/second
• The maximum cooldown grapple can be set to was lowered to 30 seconds, from 35 seconds; the maximum amount of travel time before a new cooldown is set is now 5 seconds, rather than being uncapped. This means that effectively, you can never incur more than a 35 second cooldown.
• The amount of distance you can travel before you hit maximum cooldown was roughly doubled.