Overview

Flask 3.1.1, released on May 13, 2025, fixes a secret key rotation issue and improves overall stability.

Main Features

Secret key rotation fix

Secret key rotation via SECRET_KEY_FALLBACKS is fixed to work correctly with sessions and CSRF tokens.

python 
from flask import Flask

app = Flask(__name__)
app.config['SECRET_KEY'] = 'new-secret-key'
app.config['SECRET_KEY_FALLBACKS'] = [
    'old-secret-key',  # old key still valid
]

@app.route('/')
def index():
    return 'Hello Flask 3.1.1!'

Stability fixes

Several bug fixes improve error handling and development server behavior.

python 
from flask import Flask, jsonify

app = Flask(__name__)

@app.errorhandler(404)
def not_found(e):
    return jsonify(error='Not found'), 404

# flask run --debug

Sources