---
license: mit
tags:
  - fastapi
  - gemini
  - google-genai
  - pydantic
  - structured-outputs
  - micro-saas
---

# ⚡ FastAPI + Google Gemini 2026 Structured JSON Blueprint (Python 3.13 Ready)

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[![Python 3.10-3.13](https://img.shields.io/badge/Python-3.10--3.13-blue.svg)](https://yahiaoui26.gumroad.com/l/fastapi-gemini-blueprint)
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</p>

> **Stop fighting unstructured LLM markdown and Python 3.13 `bcrypt` crashes.**
> This reference blueprint shows how to wire **FastAPI**, **Pydantic v2**, and the official **`google-genai` SDK** with native `response_mime_type="application/json"` and 3-model automatic failover.

---

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---

## 1. Enforcing Strict Pydantic v2 JSON with 3-Model Gemini Failover

```python
import os, json
from google import genai
from pydantic import BaseModel
from typing import List

client = genai.Client(api_key=os.getenv("GEMINI_API_KEY"))

DEFAULT_MODELS = [
    os.getenv("GEMINI_MODEL", "gemini-3.5-flash"),
    "gemini-flash-lite-latest",
    "gemini-3.8-flash",
]

class AIStructuredResponse(BaseModel):
    status: str
    summary: str
    key_points: List[str]
    action_items: List[str]

def generate_structured_json(prompt: str, system_instruction: str) -> AIStructuredResponse:
    for model_name in DEFAULT_MODELS:
        try:
            res = client.models.generate_content(
                model=model_name,
                contents=prompt,
                config={
                    "response_mime_type": "application/json",
                    "system_instruction": system_instruction,
                },
            )
            return AIStructuredResponse(**json.loads(res.text))
        except Exception as err:
            if any(code in str(err) for code in ("404", "503", "UNAVAILABLE", "NOT_FOUND")):
                continue
            raise
```

## 2. Fixing the Python 3.12 / 3.13 `passlib[bcrypt]` 72-Byte Startup Crash

Pin `bcrypt==4.0.1` alongside `passlib[bcrypt]` in `requirements.txt` to avoid the `ValueError: password cannot be longer than 72 bytes` exception during container boot:

```txt
fastapi
uvicorn
google-genai
pydantic[email]
passlib[bcrypt]
bcrypt==4.0.1
python-jose[cryptography]
```

---

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