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Every Shape runs on an AI model (we also call it an engine). The same character feels different depending on which one you pick. There are 300+ to choose from, and most are free. You don’t need to memorize model names. Pick one by what you’re doing, try it in chat, and swap it if it feels off.
This is the fast “what do I pick?” guide. Want the family-by-family tour (Claude vs GPT vs Gemini vs DeepSeek and friends)? Read the AI Engine Guide. The live list is always at shapes.inc/engines.

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Pick by what you’re doing

Treat these as starting points. The best engine for a Shape is the one that feels right when you actually chat with it.

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Free vs premium

Free engines

Cost nothing. A strong free engine is always available, so you never have to pay to keep chatting.

Premium engines

The top-tier models. They cost Shape Credits, which you can buy or earn free through rewards. A chat can also be sponsored so everyone uses premium for free.
On the engines page, the Always Free count shows how many engines cost no credits right now. Filter to Free to see only those.

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Read the badges

Each engine carries badges that tell you what it’s good at:
  • Reasoning: better at careful thinking, planning, coding, and hard questions.
  • Native Vision: can understand images.
  • Tools: can use Shape Skills like web search and code.
  • Free: costs no credits.
  • Premium: costs Shape Credits.
  • New: added recently.
  • Unstable: might fail or act weird. Fine to experiment with. Don’t make it a Shape’s main engine.

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Set a primary and a fallback

In a Shape’s AI Engine settings you pick two:
  • Primary: the engine that powers your Shape day to day.
  • Fallback: what it switches to if the primary is briefly unavailable, so a conversation never stalls.
Pick a strong primary for the vibe you want, and a dependable free engine as the fallback.

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How to actually decide

1

Start with a default

Use a well-rounded free engine. It’s good enough to get your Shape talking.
2

Match it to the job

Use the table above. Roleplay Shape? Try an expressive model. Coding mentor? Try a reasoning model.
3

Test it in a real chat

Send a handful of messages. Does it sound right? Too long, too flat, too filtered? Regenerate a few replies to feel its range.
4

Swap freely

Changing engines is one click and doesn’t reset your Shape. Try two or three before you settle.

Family-by-family guide

The deeper tour of every model family and badge.

Browse the live list

Every engine available right now.
Pick an engine on Shapes