What happens when a swap crosses a liquidity tick?

A tick is a discrete price boundary used by a concentrated-liquidity pool. Crossing an initialized boundary can change the active liquidity used for the next segment of a swap. The transaction can remain in the same pool throughout.

One swap, several segments

Imagine a hypothetical trade moving price upward through three regions. In the first region, positions P and Q contribute liquidity. At the next boundary, P ends and R begins. The pool then continues with a different active total. A further boundary can change that total again.

Uniswap's concentrated-liquidity documentation explains tick-based ranges, while its swap overview notes that v3 execution moves through ticks.

Why the router needs the boundaries

A quote engine cannot safely extrapolate the first segment's depth across the entire order. It needs to determine how much input reaches a boundary, update the applicable liquidity and continue the calculation for the remaining input.

This creates a piecewise calculation. The rate evolves through the curve, while the active-liquidity parameter changes at relevant boundaries. A large order may consequently have a different best route than a small order even before considering external market changes.

Do not confuse ticks with hops

A hop moves from one token to another through a venue. Crossing a tick changes the pricing segment inside a concentrated-liquidity pool. Ten crossed boundaries do not automatically mean ten separate token conversions.

Similarly, a price limit can stop a pool operation before it traverses every possible boundary. The router's final input and output conditions still determine whether the overall requested trade is satisfied.

For reading execution traces or route summaries, keep three counts separate: token hops, pool contracts and initialized tick crossings. Each describes a different aspect of the work. Detailed gas implications belong to execution-cost analysis; the routing implication is that a quote must model the liquidity actually encountered by the proposed amount.