A tick-size change can invalidate an old quote

A quote can look unchanged while the rule for submitting prices has moved underneath it. When a market sends a tick-size change, the old price grid is no longer enough to describe the next order.

The event is not a prediction about the outcome. It is a change in the set of prices the market will accept.

Save the old and new grid

Record the asset ID, old tick size, new tick size, and event timestamp together. Keep the order-book hash and the quote that was used before the change.

That small record tells you whether a later rejection came from the market moving or from a stale price increment in your own worksheet.

Rebuild the executable quote

Round the intended price to the new increment and refresh the book before deciding on size. A price that was valid under the old grid may no longer be a valid submission, even if it still looks close to the best bid or ask.

Do not turn the new increment into a directional signal. It changes order construction, not the probability of the event.

Check related constraints

Re-read minimum order size, spread, fees, and whether the market is still accepting orders. A tick change can arrive alongside a book update, so a single old snapshot may be stale in more than one field.

Keep pending orders and new orders on separate lines until the platform reports their final state.

Mark the break in your history

Label charts and backtests before and after the tick-size change. An apparent improvement in fill quality may simply reflect a finer price grid rather than a better forecast.

The useful question is not whether the new tick is smaller. It is whether your current price, size, and fill assumptions were rebuilt after the market announced the change.

Further reading: Real-time data · Market details · Order lifecycle.

Explore the markets: Open Polymarket (referral link).