Codex CLI Memory: How It Works + What Mem0 Adds

OpenAI’s Codex coding-agent product line includes a CLI, IDE extension, and ChatGPT cloud workspace, with the CLI using two main local memory layers: user-maintained AGENTS.md files for stable, hierarchical project instructions and automatically generated Memories for summaries of prior sessions stored in ~/.codex/memories/. AGENTS.md supports global and nested project files, overrides, alternate instruction filenames, and a 32 KiB cap, while Memories asynchronously extract, redact, consolidate, age out, and recall session context through markdown files rather than vector search. Native Memories are unavailable at launch in the EEA, UK, and Switzerland, remain local to one user and machine, are not designed for direct editing or team sharing, and have less publicly documented behavior in Codex’s cloud environment. The text presents Mem0, available through an MCP integration with Codex, as an external alternative offering persistent cross-machine and cross-tool storage, semantic embedding-based recall, per-user isolation, no comparable AGENTS.md size limit, and availability in regions where Codex Memories is not offered.

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