Senior Backend Python Developer - CDI - Paris

Since 2015, papernest has been transforming the way people manage their contracts, making subscription, management, and switching simple through one smart, intuitive platform.

We have supported more than 2 million customers across France, Spain, and Italy. Along the way, we have continued to invest in new verticals, establishing papernest as a high-performing, innovative, and competitive scale-up in a fast-growing market.

With over 900 employees, we are strengthening our position as a European market leader.

You will join the Telephony team, owners of the platform that powers every inbound and outbound call across papernest --- call tracking, routing, scheduling, real-time event processing and integrations with our telephony providers and Salesforce.

At papernest, AI is core to how we build. We expect every engineer to be AI-powered. You'll be a role model for AI-augmented engineering: using AI tooling fluently across the whole development lifecycle while setting the standard for safe, compliant and responsible AI usage on a business-critical system.

Main responsibilities

This is a high-impact, high-autonomy role; we are looking for a senior backend engineer to take the reins: own the architecture, raise the technical bar, and keep a system that handles business-critical call traffic reliable and fast.

You'll work mainly on our core telephony service --- an async FastAPI application following Domain-Driven Design, progressively migrating a legacy codebase toward a clean, well-specified architecture.

• Own the architecture and technical direction of the telephony backend, and drive the ongoing migration from legacy code to our DDD architecture.
• Design and build reliable, event-driven services: call tracking, scheduling, external event consumption, and provider integrations (telephony providers, Salesforce Pub/Sub).
• Write robust async Python (FastAPI, SQLAlchemy) with strong typing, full test coverage, and clear specifications.
• Make and document the hard technical calls --- data modeling, throttling, retries, failure handling --- pragmatically weighing trade-offs on a system where downtime means lost calls.
• Leverage AI tooling (Claude Code, Cursor, AI agents) to ship faster and better, and define how the team adopts AI responsibly and within our usage and security guidelines.
• Set the engineering standard: code reviews, mentoring, and lifting the team's practices around testing, observability, and CI/CD.
• Collaborate closely with Product, Ops and other engineering teams to turn business needs into solid technical solutions.
• Own your work end-to-end --- from design through autonomous deployment and monitoring in production.

About you

• 8+ years of backend software engineering, with deep expertise in Python. Telephony, real-time systems or CTI integration experience is a plus.
• Strong with our stack or close equivalents: FastAPI (or Django/Flask), async SQLAlchemy / PostgreSQL, Redis, message queues, AWS.
• An AI-powered engineer --- you use AI coding assistants and agents fluently as part of your daily workflow, and you know how to apply them responsibly and in compliance with usage, security and data-handling rules. This is a top priority for us.
• Proven track record designing and operating business-critical production backend services at scale --- async, event-driven, integration-heavy systems where reliability is non-negotiable.
• Pragmatic by nature: you make sound, trade-off-driven decisions, ship the right thing rather than the perfect thing, and know when to optimize and when to keep it simple.
• Solid grasp of software architecture (DDD a strong plus), clean code, and rigorous testing --- you treat tests, types and specs as part of the job, not an afterthought.
• Experience mentoring engineers and raising team standards.
• Fluent in English, working French is a plus.

What we offer

• 🌍 Grow in an international and inclusive environment: Everyone has their place at papernest!
• 💸 Compensation: Business Creator Share Warrants (BSPCE) package.
• 🏆 Perks: Great deals on home insurance, green electricity, and gas.
• 🩺 Health: Alan health insurance (50% covered).
• 🍽️ Meals: Swile card (€9/day, 50% funded), breakfast, and partner restaurant discounts.
• ⛳️ Sport: GYMLIB service for discounted gym membership.
• 📚 Training: Continuous training tailored to your goals.
• 📈 Career growth: Multiple paths to deepen expertise or explore new directions.
• ✨ Remote work: 2 days of remote work per week.
• ⚖️ Legal advice: Access to Ekie for personalized legal and tax advice.

Hiring Process

• First call with a Talent acquisition partner
• Interview with Julien, Engineering manager
• Technical interview with a tech lead
• Last call with Raphaël, CTO

If this is your challenge, don't miss it! We look forward to meeting you, no matter your gender, race, age, religion, disability, or sexual orientation. Our selection processes and workplace are inclusive and adapted for everyone.

Ladies, we strongly encourage you to apply! Even if you feel that you do not meet all the criteria mentioned in this offer, please note that they are only indicative. Your application will be considered with great interest. Parity and diversity are assets for our teams!