What is the best AI memory tool?

It depends on the job. Built-in memory in ChatGPT or Claude is best for preferences inside one product. Mem0, Zep and Letta are best for developers adding memory to their own agents. Memex is best for individuals who want their full conversation history from several assistants searchable and usable by any AI.

Can ChatGPT's memory be used in Claude?

Not directly. Built-in memory stays inside its product. Claude offers a memory import that brings over a text summary, and an archive such as Memex can make the full conversations available to Claude through a link or MCP.

Is Memex an alternative to Mem0?

They solve different problems. Mem0 is a developer SDK for giving an application memory of its users. Memex is a personal archive of your own AI conversations. A developer might use both: Mem0 inside their product and Memex for their own work history.

Does Memex store facts or full conversations?

Full conversations, imported from platform exports and kept in order, plus optional notes that assistants leave about which conversations were useful. Nothing is reduced to a summary unless you ask an assistant to summarize.

Knowledge Base

AI Memory Tools Compared: Built-in Memory, Mem0, Supermemory, Letta, Zep and Memex

Memex·9 min

Short answer: "AI memory" covers three different jobs. Built-in memory (ChatGPT, Claude, Gemini) remembers your preferences inside one product. Developer memory frameworks (Mem0, Zep, Letta, Supermemory) give apps and agents you build a memory of their users. Personal cross-AI archives such as Memex keep your own full conversation history from every assistant and let any AI read it. Pick by the job, not the label.

Three categories, three jobs

1. Built-in assistant memory

ChatGPT, Claude and Gemini each keep a memory of you: your name, preferences, projects and corrections. It is convenient, free with the product and requires no setup.

Its limits are structural:

It stays in one product. ChatGPT's memory does not reach Claude, and Claude's does not reach Gemini. Claude's memory import can bring over a text summary, and Anthropic labels it experimental.
It is a summary. It records that you are "working on a database migration," not the three options you compared or the error message that settled it.
The vendor decides what is kept. Claude, for example, focuses memory on work-related context.

2. Developer memory frameworks

These are building blocks for people writing AI applications:

Mem0 offers memory through APIs, SDKs and MCP, aimed at developers adding long-term memory to agents and apps.
Zep builds a temporal knowledge graph of what an application learns about its users, integrated into your application code.
Letta is an agent runtime with memory built in; you adopt its runtime to get it.
Supermemory is a hosted memory API and platform, reachable through APIs and MCP.

They are strong at what they do: extracting facts from interactions, retrieving them at the right moment, and scaling across many users of your product. They are not designed to ingest your personal ChatGPT export and make five years of your own conversations searchable.

3. Personal cross-AI archives

This category starts from your existing history. You bring exports from the assistants you already use, and the tool makes them one searchable memory that any assistant can read. Memex is in this category, and there are others with different trade-offs, such as tools that focus on extracted facts or on browser capture.

Comparison table

	Built-in memory	Developer frameworks (Mem0, Zep, Letta, Supermemory)	Memex
Primary user	Anyone using that assistant	Developers building apps and agents	Individuals and small teams using several assistants
Works across assistants	No	Yes, if you integrate them	Yes, via a link or MCP
Imports your past ChatGPT/Claude/Gemini history	No (Claude imports a memory summary)	Not the focus	Yes, from official exports
Stores	Summarized facts and preferences	Extracted memories, graphs or agent state	Full conversations, media, and AI-written notes
Setup	None	Code integration	Upload exports, copy a link
Access for AIs	Internal only	SDK, API, MCP	Markdown over HTTP, OpenAPI, MCP
Best for	Personalization inside one app	Giving your product memory	Owning and reusing your own AI history

Where Memex is the right choice

Memex fits when:

you use more than one assistant and want them to share context;
you have months or years of history in ChatGPT, Claude, Gemini, DeepSeek or WhatsApp and want it searchable;
you want the exact conversations, not a summary, available when an AI answers;
you want to own the archive, with access through links you can revoke.

Its distinctive pieces are the token-gated link that any AI can fetch, the MCP server, and breadcrumbs, which let assistants record which past conversations were useful so the archive improves with use.

Where something else is the better choice

Be honest about the fit:

If you only use one assistant and mostly want it to remember your preferences, its built-in memory is enough.
If you are building a product whose users need memory, start with a developer framework like Mem0, Zep or Letta.
If you need enterprise-wide knowledge management across documents and tickets, a dedicated enterprise search or knowledge platform is a better base than a conversation archive.

Many people combine categories: built-in memory for preferences, Memex for history, and a framework inside whatever they are building.

How to evaluate any AI memory tool

Ask these questions before committing:

Can I get my data out? Export in an open format should be a given.
Does it start from my existing history, or only from today?
Which assistants can read it, and by what mechanism: extension, API, MCP?
What does it store: full text, summaries, or extracted facts? Summaries lose detail; full text keeps it.
Who can access it, and can I revoke that access instantly?

Descriptions of third-party tools reflect their public positioning as of the date above and may change; check each vendor's documentation for current features.