Some frequent Lyft users are being offered monthly subscription plans.

The plans have been tested at different price points for the past few months, offering "free" rides for a lump sum up front. Rides are capped at $15, so this is for short, frequent trips -- not long-distance trips to the airport.

A Lyft spokesperson said in an email Friday, "We’re always testing new ways to provide passengers the most affordable and flexible transportation options. For the past few months, we’ve been testing a variety of All-Access Plans for Lyft passengers."

Lyft users posted invite-only emails they received over the past few days. Some were offered a $400 monthly plan for up to 60 rides while others received a weekly $50 plan with seven rides. Another user was targeted with a $300-for-30-rides plan.

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Yet another price point: $199 for 30 rides in a month.

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The Lyft support account explained that trips over $15 would get charged to the card on file. So no free rides to the airport, but it would be a $15 discount.

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Lyft didn't say when or if the subscriptions would become available to everyone, but the company is clearly trying to collect data on what works.