# Lots and Consumption Window

On The Grid, purchased Units are grouped into Lots when they enter your Consumption Account. Each Lot has a 4-hour Use It or Lose It window: tokens not consumed within that window expire permanently. \
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This perishability is a deliberate design choice - it gives suppliers confidence that demand is real and near-term, which lets them price aggressively, and it prevents capacity hoarding that would distort the market.

### What are Lots?

When Units leave your Trading Account, either through a [Scheduled Sweep](https://thegrid.ai/docs/introduction/core-concepts/scheduled-sweeps) or a voluntary transfer, they are grouped into **Lots** in your Consumption Account. Each Lot:

* Represents a **specific quantity** of Units.
* Has a fixed **4 hour expiry**.
* Is consumed on a **first in, first out (FIFO)** basis. The system always spends from the Lot that expires soonest.

### Why 4 hours?

The 4 hour window is a deliberate design choice:

* It gives suppliers strong certainty that any Units they sell will either be used quickly or expire, which lets them price more aggressively and predictably.
* It is long enough to cover typical interactive usage and near term batch jobs, including workloads scheduled around predictable troughs.

If a Lot reaches the end of its 4 hour window with leftover tokens, those tokens expire and are no longer usable or refundable. This use it or lose it rule is a core part of the market discipline.