2025 has been a tough year for electric vehicle stocks. Companies like Lucid Group and Tesla have seen their valuations plummet. Rivian's (RIVN 4.42%) decline hasn't been quite as steep, but that's because its stock was already trading at a deep discount compared to those competitors.

There are several good reasons why Rivian's valuation is so low, but its stagnating revenue growth tops the list. Looking ahead, however, there's reason to expect its sales growth should spike starting in 2026 thanks to one exciting factor.

Affordable new models will reinvigorate Rivian's growth

Rivian has done a terrific job scaling up its electric vehicle business. The company currently has two luxury models in production, and while those vehicles were panned for reliability by testers from Consumer Reports, the magazine's customer surveys showed that Rivian owners were more satisfied with their vehicles than owners of any other brand. Last quarter, Rivian also achieved a positive gross margin for the first time -- a huge milestone on its path to long-term financial stability.

Still, the company's valuation remains significantly below competitors like Tesla and Lucid due to its lackluster sales growth estimates. And that may offer a huge opportunity to investors.

RIVN PS Ratio data by YCharts.

While analysts expect minimal sales growth from Rivian this fiscal year, there's good reason to believe that sales growth will pick up considerably starting in 2026. That's because Rivian expects to begin production of three new mass-market vehicles early next year, all of which should cost less than $50,000. Offering vehicles in that price range should be a huge inflection point for its business, at least if Tesla's history offers any indication. After Tesla launched its first mass-market vehicles -- the Model Y and Model 3 -- its sales went on to double and then triple in the years that followed.

Once Rivian's affordable models hit the market in 2026, I expect its sales growth will accelerate rapidly. This should occur across a 12-month to 24-month time frame. Analysts, meanwhile, usually focus their estimates on the next 12 months. That has helped create an opportunity for patient investors to get in on Rivian at a good price now.