The new fares — called “Go,” “Go Savvy,” “Go Comfy” and “Go Big” — will be available to book starting Aug. 16. Some perks will not be available on flights until Aug. 27.

The changes mark a major departure from Spirit’s “unbundled” approach, which advertised rock-bottom ticket prices but left travelers to pay for extras from picking a seat to a cup of soda to carry-on bags. Spirit still will sell a category of ticket that allows only a personal item.

“We’re unveiling a new era in Spirit’s history and taking low-fare travel to new heights with enhanced options that are unlike anything we’ve offered before,” Ted Christie, the airline’s CEO, said in a news release. “We listened to our Guests and are excited to deliver what they want: choices for an elevated experience that are affordable and provide unparalleled value.”

Spirit already had announced in May that it was doing away with fees to change or cancel a flight. Passengers previously had to pay $69 to $119, depending on when the change was made; there was no charge 60 or more days from departure.

As part of the changes announced Tuesday, Spirit also is tweaking its boarding process and introducing priority check-in for some travelers at select airports starting Aug. 27. The airline announced the new offerings as “part of a significant transformation that delivers an even friendlier, more comfortable, and cost-effective travel experience.”

Since the pandemic, Spirit has faced rapidly rising costs, slow revenue growth and a big debt bill due in 2025. It had hoped a merger would solve its problems, but it ended such plans with JetBlue in March, after a federal judge blocked the move on antitrust grounds.

The premise behind the airline’s new fares is simple: Presented with an option for more perks, like assigned seats or checked bags, most travelers prefer spending a bit more over buying the cheapest option. Major airlines like American and Delta saw this when they introduced no-frills basic economy fares in the last decade.

Jungho Suh, a teaching assistant professor of management at the George Washington University School of Business, said Spirit’s move makes strategic business sense but comes with risk.

“It’s risky by diluting their brand identity, which is budget-traveler-friendly,” he said.

The airline faces significant pressure from Wall Street to boost revenue quickly. Many analysts warn that Spirit could file for Chapter 11 bankruptcy to address more than $1 billion in debt due next year.

In the meantime, Spirit’s financial outlook is worsening. The airline told investors earlier in July that its “non-ticket revenue” — what it makes from charging for things like checked bags and assigned seats — was lower than expected during the three months ending in June.

“We believe [that drop] primarily relates to the removal of change fees and Frontier’s new bundled offering,” Savanthi Syth, an airline analyst at investment bank Raymond James, wrote in a report July 16.

Spirit competitor Frontier Airlines rolled out changes to its model in May, offering a handful of fare categories with perks built in at higher prices. Southwest announced last week that it will move away from its open-seating policy and instead sell assigned seats, including premium options.

Spirit remains a budget airline even with the changes, said Brett Snyder, who runs the air travel blog Cranky Flier and the travel planning company Cranky Concierge. The carrier is not, for example, making any changes to its core offering, which includes some of the tightest legroom of any U.S. airline.

“Spirit is just trying to make it easier for people to fly them,” Snyder said.