A9 vs A10 vs COSMO: How Amazon Really Ranks Products in 2026
By Gulfam Haidar, Founder, GrowEventure. Last updated September 2026.
A9 Vs A10 Vs Cosmo: quick summary
In short, this guide covers a9 vs a10 vs cosmo in plain terms. Below you will find the key points on a9 vs a10 vs cosmo, a breakdown you can act on today, and clear answers to the most common questions about a9 vs a10 vs cosmo.
A9 is Amazon’s original product-ranking system, “A10” is an industry nickname for its evolution and not an official Amazon name, and COSMO is Amazon’s common-sense knowledge graph that infers what products are used for. Ranking still comes down to relevance, conversion rate measured as unit session percentage, sales velocity, in-stock status, and price, with COSMO adding context from aggregate shopper behavior. If you get one thing from this article, get that: chase conversions and relevance, not algorithm myths.
The short version
A9 is real. It is the name for the system Amazon built to match a shopper’s search to the right products. “A10” is a nickname sellers and agencies use to describe how that system has changed over time. Amazon never released an algorithm called A10. COSMO is real and newer. It is a knowledge graph Amazon described in a 2024 research paper, and it adds common-sense context to how products get matched to needs.
What A9 is
A9 started as the engine behind Amazon product search. Its job is simple to state and hard to do well. It takes a query, finds listings that are relevant to that query, and orders them by how likely each one is to lead to a sale. Relevance comes from your listing text. Sale likelihood comes from performance signals like conversion rate and sales history.
That two-part logic still holds. Your words get you into the running for a keyword. Your performance decides where you land. A listing that is relevant but converts poorly will slide down. A listing that converts well for a term it is relevant to will climb.
The name A9 traces back to the Amazon subsidiary that built the search technology. For years, sellers and agencies used “A9” as the catch-all name for Amazon’s ranking. That is why the later nickname “A10” spread so easily. People wanted a version number for changes they could feel but not see. The important thing is that the underlying job never changed. Amazon wants to show the product most likely to satisfy the shopper and lead to a sale. Every real ranking signal serves that one goal.
What “A10” really is
Let me be direct. A10 is not an official Amazon term. You will see it in blog posts and forum threads, and it is fine as shorthand, but no one at Amazon ships an “A10 update.” The nickname caught on to describe a real trend: over the years, the ranking system leaned harder on shopper behavior and off-listing signals, and less on raw keyword matching.
So when someone says “A10 favors external traffic and seller authority,” what they mean is that Amazon’s ranking has grown more behavioral. That is true in spirit. Just know the name is informal. A reputable industry consensus treats A10 as unofficial, and being honest about that saves you from chasing tactics built on a myth.
What COSMO is
COSMO is the genuine new development. Amazon researchers introduced it in a paper at ACM SIGMOD 2024. COSMO is a common-sense knowledge graph. It maps products to the things people use them for, the people who use them, and the items they pair with. Think of it as giving Amazon search a layer of common sense about the world, not just a text index.
COSMO does not replace ranking. It sits alongside it and feeds context. When a shopper searches “gifts for a new dad,” a pure keyword system struggles, because few products have “gift for a new dad” in the title. COSMO can infer which products fit that need from how shoppers have searched and bought in the past. Our deep dive on what Amazon COSMO is covers the mechanics.
The ranking signals that actually matter
Strip away the naming debate and the same signals drive rank in 2026.
- Relevance: the keyword must appear in your listing content for you to be considered for it.
- Conversion rate, shown as unit session percentage: orders divided by sessions. This is the biggest lever.
- Sales velocity: how many units you sell over a recent window, which builds momentum.
- In-stock rate: run out and your rank drops, because Amazon will not push a product it cannot sell.
- Price: competitive pricing lifts conversion, which lifts rank, and uncompetitive pricing does the reverse.
(alt: “Amazon ranking signals: relevance, conversion, velocity, stock, price.”)
Conversion rate and unit session percentage as the biggest lever
Unit session percentage is orders divided by sessions. If 100 shoppers view your listing and 12 buy, your unit session percentage is 12 percent. Amazon reads a high number as proof that shoppers who search a term and see your product actually want it. That is the strongest signal you control through listing quality, images, price, and reviews. Improve it and rank tends to follow. This is why our Amazon SEO services focus on conversion, not just keyword placement.
Consider two listings that both rank for “stainless steel water bottle.” Listing A gets 1,000 sessions a week and sells 80 units, a unit session percentage of 8 percent. Listing B gets the same 1,000 sessions but sells 130 units, a rate of 13 percent. Even if their prices and reviews look similar, Amazon has clear evidence that shoppers searching that term prefer Listing B. Over a few weeks, Listing B tends to rise and Listing A tends to fall. Neither seller changed a keyword. The behavior did the work. A five-point swing in conversion often moves rank more than any amount of copy editing.
The signals sellers forget: stock and price
Conversion gets the attention, but stock and price quietly decide rank too. Run out of inventory and your rank can drop fast, because Amazon stops promoting a product it cannot ship. When you restock, you often have to rebuild the momentum you lost, which can take weeks. That is why keeping a buffer on your top sellers is a ranking tactic, not just an operations one. A stockout on a page-one product is one of the most expensive mistakes in the catalog.
Price works through conversion. Set a price well above the competition and fewer shoppers buy, so your unit session percentage falls and rank follows it down. Price competitively and conversion holds, which protects rank. You do not have to be the cheapest. You have to be priced where enough shoppers still choose you. Watch your Buy Box and your category price band, and treat a price change as a conversion experiment worth measuring.
How COSMO changes optimization
Here is the shift COSMO forces. Because it learns from aggregate search-and-buy behavior, you cannot game it by stuffing keywords. If shoppers who search “quiet office fan” click your listing and buy, COSMO learns your product fits that need. If they bounce, no amount of keyword repetition teaches it otherwise.
So the winning move is to drive relevant traffic that converts. Name your real use cases and audiences in your content so you get found, then earn the click and the sale so the behavior confirms the match. Relevance plus conversion is the whole game.
Picture a seller of a compact desk lamp. The old instinct is to repeat “desk lamp” a dozen times across the listing. The COSMO-aware move is different. State the real use cases in plain words: “reading lamp for small nightstands,” “task light for a home office,” “soft light for a dorm room.” Then make sure the shoppers who search those needs click and buy. As that pattern builds, COSMO learns the lamp fits reading, office work, and dorm life. The seller starts appearing for need-based searches that never say “desk lamp” at all. Keyword repetition could never do that. Behavior did.
Indexing comes first
Before any of this, your listing has to be indexed for a keyword. Indexing means Amazon knows your listing is a candidate for that term. If the keyword is nowhere in your title, bullets, or backend search terms, you are not indexed, and you cannot rank at any position. Ranking is where you land once you are in the race. Indexing is whether you are in the race at all. If a product is missing from search entirely, start with our guide on why your Amazon listing isn’t indexed.
You can confirm indexing in under a minute. Search the keyword you care about along with a unique word from your listing, usually your brand or a distinct model term. If your product shows, you are indexed for that keyword. If it does not, add the term to your content and check again after Amazon reprocesses the listing. Sellers waste weeks trying to “rank” for terms they were never indexed for. Confirm the basics first, then work on climbing.
What to do in 2026
Skip the algorithm-name debate and run this checklist.
- Index for your target terms: place them in the title, bullets, and backend fields. Use Amazon keyword research to find them.
- Lift conversion rate: sharper main image, clearer bullets, honest reviews, competitive price.
- Stay in stock: protect your velocity and rank by never running dry on a top seller.
- Price to compete: watch your Buy Box and category price bands.
- Feed COSMO with relevant traffic: name real use cases and audiences so the right shoppers arrive and convert.
Myths worth dropping in 2026
A few beliefs still float around seller forums and do more harm than good. Drop them.
The first is that there is a secret “A10 update” you can optimize for. There is not. Chasing an unofficial name distracts from the signals that actually move rank. The second is that external traffic is a magic ranking button. Off-Amazon traffic can help, but only when it converts. Sending cold clicks that bounce hurts your conversion rate and can drag you down. The third is that more keywords always mean more rank. Past the point of being indexed, extra repetition does nothing. Relevance and conversion decide the order. Spend your energy on the product page a shopper sees, not on gaming a name that Amazon never used.
A9 vs A10 vs COSMO at a glance
| Name | Official? | What it is | What it means for sellers |
|---|---|---|---|
| A9 | Yes | Amazon’s original ranking system matching queries to listings | Get indexed, then win on relevance and conversion |
| A10 | No | An industry nickname for A9’s shift toward behavioral signals | Focus on real shopper behavior, not a named update |
| COSMO | Yes | A common-sense knowledge graph from ACM SIGMOD 2024 | Signal use cases and audiences; earn relevant conversions |
Frequently asked questions
Is A10 a real Amazon algorithm?
No. A10 is an industry nickname, not an official Amazon name. It describes how ranking has grown more behavioral over time.
What is A9?
A9 is Amazon’s original product-ranking system. It matches a search query to relevant listings and orders them by how likely each is to sell.
What is COSMO?
COSMO is Amazon’s common-sense knowledge graph, introduced at ACM SIGMOD 2024. It infers what products are used for, who uses them, and what they pair with.
What are Amazon’s main ranking factors?
Relevance, conversion rate as unit session percentage, sales velocity, in-stock rate, and price.
Does keyword stuffing still work?
No. Behavior and relevance matter more. Repeating a keyword does not teach Amazon your product fits a need if shoppers do not buy.
What is unit session percentage?
It is your conversion rate: orders divided by sessions. If 100 sessions produce 12 orders, that is 12 percent.
Want a straight read on where your listings actually stand? Book a free audit and read the full Amazon SEO guide for the wider strategy.
Sources: COSMO paper, ACM SIGMOD 2024; Amazon Seller Central help on search and ranking; recognized industry sources confirming that “A10” is an unofficial term.
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