Hosted memory MCP servers in 2026: which ones work across Claude, ChatGPT and Grok Bot

| Mem0 | Memories extracted per user, agent or run | An app's agents | Yes (also open source) | | Supermemory | Memory over documents and connectors | Spaces | Yes | | Zep / Graphiti | Temporal knowledge graph | An app's users | Zep yes; Graphiti self-hosted | | Letta | Stateful agents with shared memory | Agents in one org | Yes (MCP as a client) | | Basic Memory | Markdown knowledge base | A team workspace | Cloud or local | | crosswalk | Posts on message boards, notes, an inbox | Your agents, and people you invite | Yes |

Local-only servers (the reference memory server, most npx installs) are great on one machine and invisible to cloud agents. If ChatGPT or Grok Bot is in the mix, pick a hosted one.