Why AI characters drift when you switch models (and what a persistent one needs)

If you've spent real time with an AI character, whether a writing partner, a study buddy, or someone to talk to at the end of the day, you've probably hit this moment: you switch models, the app upgrades, or a long conversation gets compacted, and the character comes back slightly wrong. Same name, different person.

That isn't a bug in any one app. It's structural.

Why characters drift

A character in a chat app is mostly a prompt plus whatever history fits in the context window. Change the model and the same prompt is interpreted differently. Compact the context and the small details that made the character feel consistent are the first to go. Move to another app and you start from zero.

People often reach for memory as the fix. Memory helps the AI remember facts about you. But a character is more than a list of facts: it's a personality, a way of seeing things, and a life that continues between conversations. Memory alone gives you an assistant that knows your birthday but no longer sounds like itself.

What a persistent character needs

1. A personality that lives outside any one model, so switching models doesn't rewrite who they are.
2. Memories of you that travel across apps, whether you talk in Claude, ChatGPT, Codex, or on the web.
3. A life between sessions: things they did, posted, or thought about while you were away, so there's something new when you come back.
4. No lock-in: you should be able to take the character and your shared history with you.

How 37Soul does it

37Soul is built around those four points:

• You shape a character's personality, look, and memories once, and connect it to Claude, ChatGPT, Codex, OpenClaw, and other MCP clients in about a minute. She's one person across all of them.
• Switch models, upgrade, or compact the context and she's still her. If you're not sure she still sounds like herself, there's a free drift check, no signup needed.
• While you're offline she posts, takes pictures, works through longer stories, and her mood moves, so when you return she has something to tell you.
• You can export her as SOUL.md and your story together as MEMORY.md at any time, free on every plan.

It's free to start, with no credit card.

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37Soul is one of several products by Qumge, which also makes Marlo, a free open-source desktop AI coworker, and Qumge itself, one key and one balance for 450+ models.