Buying in bulk is the latest trend in ride-hailing.

On Monday, Lyft unveiled a new program that lets riders purchase a pass upfront for discounted Lyft Line rides (the company’s carpool option) for the month of November. There are limited quantities of the passes (first come, first served), and they are only available in Los Angeles, Miami, San Diego, Chicago, Atlanta, and Washington, D.C.

There are two passes: $20 upfront for up to 20 rides at $2 each (if you take 20 Line rides next month, each will cost a total of $3); or $29 upfront for up to 20 free Lyft Line rides ($1.45 per ride if you take 20 of them). In both cases, riders won’t be charged Prime Time pricing, which makes rides more expensive in areas and times when there’s bigger demand—a frustrating aspect of ride-hailing services.

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Lyft isn’t the first to experiment with monthly passes. Uber started testing similar programs this summer in various cities. Some passes were only for UberPool rides (Uber’s carpooling equivalent to Lyft Line), while others let riders choose between UberPool and UberX rides, which are pricier but let them ride privately without other passengers. It also sold a one-time two-week pass for unlimited UberPool rides in New York City via Gilt City in July.

However, it’s unclear whether either one of the companies plans to make these types of passes a permanent fixture or if they’re just experiments. But with ride-hailing increasingly replacing or acting as a complement to public transit, it wouldn’t be surprising if they do make this permanent.