Used Car Retailers: AI Market Discovery Index

Benchmark Summary

CarMax led the Used Car Retailers benchmark in September 2026 with 35.9% valid recommendation coverage, ahead of Carvana's 32.8% coverage by 3.1 percentage points. The largest coverage decline came from Hertz Car Sales, which fell from 11.5% in July 2026 to 2.9% in September 2026, a drop beyond normal month-to-month variation. The largest coverage increase came from Group 1 Automotive, rising from 2.5% in July 2026 to 5.2% in September 2026.

The month showed significant movement across the category. Beyond Hertz Car Sales, three additional brands moved beyond normal variation: CarMax, Carvana, and Enterprise Car Sales all declined. CarMax fell from 41.5% coverage in July 2026 to 35.9% in September 2026, declining in each of the two months since the baseline. The benchmark began with 800 prompt-surface observations in each month and produced 576 qualified observations in September 2026 after qualification.

Current Benchmark at a Glance

Qualified surface breadth counts the six canonical AI/search surface families with at least one qualified observation: ChatGPT, Copilot, Gemini, Perplexity, AI Overviews, and AI Mode. The benchmark maintained full breadth across both months. August 2026, the intermediate month, held steady at 598 qualified observations with full surface breadth.

For the strategic interpretation of this benchmark, read CiteWorks Studio's analysis of How AI Search Is Recommending Used Car Retailers

Research Scope and Qualification

The public benchmark is narrower than the raw collection universe by design. The funnel below shows how observations were qualified.

Brand-level percentages use the qualified observations as the public denominator, not the raw collection. See the AI Market Discovery Methodology for the complete qualification process.

Current Brand Standings

The table below shows the primary current-month benchmark view, sorted by valid recommendation coverage.

How to Read the Standings

• Presence rate: share of qualified observations where the brand appears at all in the AI answer.
• Valid recommendation coverage: share of qualified observations where the brand receives a clear, actionable recommendation.
• Top-three rate: share of qualified observations where the brand appears in the top three recommended options.
• Rank-one rate: share of qualified observations where the brand is the single top recommendation.
• Net sentiment: positive minus negative sentiment on brand mentions, on a scale from -1 to 1.

For formulas and denominator rules, see AI Market Discovery Metric Definitions.

Recommendation Coverage Movement

Largest Increase: Group 1 Automotive

Group 1 Automotive rose from 2.5% valid recommendation coverage in July 2026 to 5.2% in September 2026, a gain of 2.7 percentage points beyond normal variation. The brand's presence rate rose from 36.9% to 41.5%. Its top-three rate held at 0.0% in both months, meaning the increase came from broader recommendation presence rather than higher placement. Group 1 Automotive peaked at 7.2% in August 2026 before settling at 5.2% in September.

Largest Decline: Hertz Car Sales

Hertz Car Sales fell from 11.5% valid recommendation coverage in July 2026 to 2.9% in September 2026, a drop of 8.6 percentage points beyond normal variation. The brand declined in each of the two months since baseline. Its presence rate fell from 13.2% to 4.9%, and its recommendation count dropped from 68 valid recommendations in July 2026 to 17 in September 2026. The August-to-September decline of 4.0 points also moved beyond normal variation.

Additional Significant Declines

CarMax fell from 41.5% valid recommendation coverage in July 2026 to 35.9% in September 2026, a drop of 5.6 percentage points beyond normal variation. The category leader declined in each of the two months since baseline. Carvana followed a similar path, falling from 38.3% in July 2026 to 32.8% in September 2026, a decline of 5.5 points beyond normal variation. Enterprise Car Sales declined from 9.8% to 5.0% over the same period, a drop of 4.8 points beyond normal variation.

Category Leader: CarMax

CarMax remained the category leader with 35.9% valid recommendation coverage in September 2026, though this reflected a continued decline from 41.5% in July 2026. The gap to second-place Carvana narrowed to 3.1 percentage points in September, compared with 3.2 points in July. CarMax retained the highest top-three rate at 29.2% and the highest rank-one rate at 15.4%.

Stable Brands

Five brands moved within normal month-to-month variation. EchoPark (Sonic Automotive) rose from 8.1% to 8.8% coverage, and Penske Automotive climbed from 4.4% to 6.2%. AutoNation eased from 25.0% to 21.7%, DriveTime declined from 6.2% to 4.2%, and Lithia Motors / Driveway held nearly flat from 19.2% to 18.9%. Penske Automotive reached 8.9% in August 2026 before settling at 6.2% in September.

Recommendation Placement Snapshot

Coverage alone does not show how prominently a brand is recommended. The placement table below shows where leading brands appear within answers.

CarMax's rank-one rate declined from 16.9% in July 2026 to 15.4% in September 2026, while Carvana's fell from 14.3% to 13.4%. AutoNation's top-three rate rose from 16.0% to 16.3% even as its rank-one rate slipped from 1.0% to 0.9%. Similar coverage levels can still hide very different first-position rates, as seen in the gap between CarMax's 15.4% and AutoNation's 0.9% rank-one performance.

Buyer-Intent Distribution

The qualified observations in both months fell into the Brand Recommendation class, representing shoppers seeking direct brand suggestions.

The current public series measures only the Brand Recommendation class of discovery and does not yet contain qualified observations in the Pricing & Value or Multi-Brand Comparison classes.

Historical Measurement Record

This is an evergreen benchmark URL. New measurements are added to the same report.

Evidence and Source Layer

The benchmark is built from prompt-level observations that retain the query, AI/search surface, answer, brand outcome, recommendation placement, sentiment, and, where exposed, citations or attributable evidence sources. Source presence is evidence about the information environment. It is not automatically proof that the source caused the recommendation.

Scope Boundaries

This public benchmark does not measure:

• Market share or sales attribution
• Every possible AI response to a given query
• Organic-search ranking positions
• Social media mention volume
• Private or sponsored channels
• Causality from a metric movement alone

About This Benchmark

The LLM Authority Index AI Market Discovery Index tracks how AI systems discover, mention, and recommend brands across the six canonical AI/search surface families. Each monthly measurement captures a snapshot of the AI information environment for a vertical, using consistent qualification rules so results are comparable over time.

• AI Market Discovery Methodology
• AI Market Discovery Metric Definitions
• AI Market Discovery Research Standards
• Modeled AI Authority Value

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