Mem0 vs Zep vs Letta: Memory Layer, Graph or Agent?
On this page, 10 sections
Mem0, Zep and Letta are usually listed as three versions of the same thing. They are not. Mem0 is a memory layer you add to an agent. Zep is a hosted memory service built on a graph.
Letta is a platform for building agents that keep their own state. Picking between them without knowing that is how people end up rewriting an integration in month two.
This comparison uses each project’s own README, docs and pricing page, plus the GitHub API, all read on 11 October 2026. I have not run these three in production, so there are no “I tested it” claims here, and where a page is silent I say so.
The short answer
Pick Mem0 if you want to bolt memory onto an agent you already have. Pick Zep if your facts change over time and you want the history kept, and you are happy to pay for a hosted service.
Pick Letta if you want the agent itself to be the product, with memory as part of how it works. If you only need a self-hosted memory store, check what Zep still ships as open source before you choose it, because that changed.
What each one is
Mem0 is a memory layer. The repo is mem0ai/mem0, licensed Apache-2.0, with 66,978 stars. The last push was 9 October 2026. That is more than twice the stars of any other repo in this comparison.
Zep needs a careful read. The repo getzep/zep is, per its own README, examples and integrations for Zep Cloud, not the product itself. Zep published a post announcing that it stopped maintaining and releasing the Zep Community Edition.
The existing repository stays open under Apache-2.0, but with no updates or active support. Zep’s open source effort now goes to Graphiti, a temporal knowledge graph framework, which the post says powers Zep’s commercial service. Graphiti is getzep/graphiti, Apache-2.0, with 31,640 stars. The getzep/zep repo has 4,955.
Letta is the project formerly known as MemGPT. Its README says the current source lives in letta-ai/letta-code. The older letta-ai/letta repo is Apache-2.0 with 25,102 stars, last pushed 10 September 2026. Letta’s docs call it a platform for building stateful agents, and say the agent harness is open source.
If you want the wider field, my overview is AI memory tools compared.
Side by side
| Item | Mem0 | Zep | Letta |
|---|---|---|---|
| What it is | Memory layer | Hosted memory service on a temporal graph | Stateful agent platform |
| Open source repo | mem0ai/mem0, Apache-2.0 | Graphiti, Apache-2.0 (Community Edition discontinued) | letta-ai/letta-code, plus the older letta-ai/letta |
| GitHub stars (11 Oct 2026) | 66,978 | 31,640 (Graphiti), 4,955 (getzep/zep) | 25,102 (letta-ai/letta) |
| Free tier | Hobby, free | 10,000 credits a month | $0, up to 3 stateful agents, bring your own key |
| First paid tier | Starter, $19 a month | Flex, $125 a month | Pro, $20 a month |
Pricing, read on 11 October 2026
Mem0’s free Hobby plan allows 10,000 add requests and 1,000 retrievals a month. Starter is $19 a month with 50,000 add requests and 5,000 retrievals. Pro, marked “Popular”, is $249 a month with 500,000 add requests and 50,000 retrievals, and it includes graph memory. Enterprise is custom. Note the jump: graph memory sits behind the $249 tier, not the $19 one.
Zep prices in credits. There is a free tier with 10,000 credits a month. Flex is $125 a month with 50,000 credits, and Flex Plus is $375 a month with 200,000 credits. I did not work out what a credit buys for your workload, and neither will you from the headline numbers. Run a trial and read the usage.
Letta’s Free plan is $0, limited to 3 stateful agents, and you bring your own model key. Pro is $20 a month. Teams Pro is $20 per seat a month. API usage is billed at $0.10 per active agent a month and $0.00015 per second of tool execution.
These three bills are not comparable line by line. Mem0 meters requests, Zep meters credits, Letta meters agents and tool seconds. Estimate your own volume in each unit before you compare.
Benchmarks
Mem0’s README reports 92.5 on LoCoMo and 94.4 on LongMemEval. The same README says these are scores for the Mem0 managed platform, which includes optimizations that are not in the open source version, and that the benchmark framework itself is open sourced.
So the headline number does not describe what you get if you self-host. I did not find comparable numbers for Zep or Letta in the pages I read, so I am not ranking the three on benchmarks.
Which one for which job
You have an agent and want it to remember users. Mem0. It is the least invasive: you add memory calls around an agent you already built. Start on the free plan and watch the retrieval count, because 1,000 retrievals a month goes quickly in a busy chat product.
Your facts change and the history matters. Zep, or Graphiti if you want to run it yourself. Customer addresses, plan changes and status changes are examples where “what was true last month” is a real question.
Graphiti is built around temporal data, per Zep’s own description. The tradeoff is that the self-hosted route means you run the graph yourself, and the maintained open source piece is the framework, not the old service.
You want the agent itself to learn and persist. Letta. It is closer to an agent runtime than a memory plug-in. If all you wanted was a memory API, Letta is more than you need.
You are comparing graph-first tools. The two-way read is in Cognee vs Supermemory, and the local-first angle is in Mem0 vs MemPalace.
If you are still choosing a category, start with the best AI memory layer for agents.
What I could not verify
- Production quality, latency or uptime for any of the three. I did not test them.
- Whether Zep’s credit pricing is cheaper or dearer than Mem0’s request pricing for your workload.
- Benchmark results for Zep and Letta. I did not find them in the pages I read.
- How actively the older letta-ai/letta repo is maintained now that the README points to letta-code.
Do this today
- Write down what your agent must remember and whether those facts ever change.
- Count your monthly add and retrieval calls, or your active agents. That is the number each pricing page needs.
- Run the free tier of the one that matches your job from the section above.
- Feed it 20 real conversations and ask 20 questions you know the answers to.
- Count correct answers, then check the bill estimate against the pricing page.
Frequently asked questions
Is Zep open source?
Partly. Zep stopped maintaining and releasing its Community Edition. The old repository stays open under Apache-2.0 without updates. The open source effort now goes to Graphiti, which has 31,640 stars on GitHub.
Is Letta the same as MemGPT?
Letta’s README says it is formerly MemGPT. Its README also says the current source lives in the letta-code repository.
Which has the most GitHub stars?
Mem0, with 66,978 on 11 October 2026. Graphiti has 31,640 and letta-ai/letta has 25,102. Stars measure attention, not fit.
Does Mem0 include graph memory on the cheap plan?
On the pricing page I read, graph memory appears in the $249 a month tier, not in the $19 Starter plan.