Leanstral 1.5 API

mistral/labs-leanstral-1-5
Mistral AI's Lean 4 formal proof engineering model — built for automated theorem proving and autoformalization.
Context
256K tokens
Input
Output
Released
Jun 30, 2026

How to use Leanstral 1.5 API

Install any OpenAI-compatible SDK, point it at api.aimlapi.com/v1, and set the model to mistral/labs-leanstral-1-5.
import requests

r = requests.post(
    "https://api.aimlapi.com/v1/chat/completions",
    headers={"Authorization": "Bearer " + AIMLAPI_KEY},
    json={
      "model": "mistral/labs-leanstral-1-5",
      "messages": [
        {
          "role": "user",
          "content": "Hello!"
        }
      ]
    },
)
print(r.json())
const r = await fetch("https://api.aimlapi.com/v1/chat/completions", {
  method: "POST",
  headers: {
    Authorization: `Bearer ${process.env.AIMLAPI_KEY}`,
    "Content-Type": "application/json",
  },
  body: JSON.stringify({
    "model": "mistral/labs-leanstral-1-5",
    "messages": [
      {
        "role": "user",
        "content": "Hello!"
      }
    ]
  }),
});
console.log(await r.json());
curl -X POST https://api.aimlapi.com/v1/chat/completions \
  -H "Authorization: Bearer $AIMLAPI_KEY" \
  -H "Content-Type: application/json" \
  -d '{"model":"mistral/labs-leanstral-1-5","messages":[{"role":"user","content":"Hello!"}]}'

OpenAI-compatible — swap the base URL and it works with your existing SDK.

Leanstral 1.5 API Pricing

TypePrice
Output

Frequently asked questions

Leanstral 1.5 has a 256,000 tokens context window.

Leanstral 1.5 takes text as input and returns text.

Use mistral/labs-leanstral-1-5 as the model id. Requests go to https://api.aimlapi.com/v1/chat/completions.

Leanstral 1.5 became available on June 30, 2026.

Yes, Leanstral 1.5 can stream responses as they are generated.

Leanstral 1.5 was built by Mistral AI.

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