---
title: 'Principal Research Engineer, Model Training & Post-Training at Inflection AI'
canonical: 'https://feeny.ai/job/principal-research-engineer-model-training-post-training-inflection-ai-palo-76x0eww37ac8'
type: 'job'
last_seen: '2026-09-08'
---

# Principal Research Engineer, Model Training & Post-Training at Inflection AI

- **Company:** Inflection AI
- **Location:** Palo Alto California, United States
- **Posted:** 2026-06-29
- **Last confirmed live:** 2026-09-08
- **Apply:** https://boards.greenhouse.io/inflectionai/jobs/4693117006?gh_jid=4693117006

## Job description

## About Inflection AI

Inflection AI is a Public Benefit Corporation empowering people with human-centered, emotionally intelligent AI. We’re shaping the future of AI by combining emotional intelligence (EQ) and raw intelligence (IQ) to elevate people’s potential.

Inflection AI created Pi, the world’s first emotionally intelligent AI, to help people work through decisions, emotions, and challenges. Pi is a personal AI agent powered by Inflection AI’s foundation model, proving that AI can be personal, empathetic, and contextually aware.

## About the Role

Inflection’s models are central to our product and platform strategy, and we are looking for a hands-on technical leader to own the model-improvement loop from data and training through evals, post-training, release criteria, and production feedback. This person will sit at the intersection of research, production engineering, and model release, with a mandate to ship models that are measurably better for users. The ideal candidate has led serious model training or post-training work before, can make principled tradeoffs across data, compute, architecture, and quality, around a clear technical roadmap.

## What You’ll Do

- Own the model-improvement roadmap across capability, reliability, emotional intelligence, tool use, safety, latency, cost, and enterprise readiness.
- Lead training and post-training strategy, including supervised fine-tuning, RLHF, DPO, GRPO, RLAIF, reward modeling, preference optimization, tool-use fine-tuning, distillation, synthetic data, and related methods.
- Drive model architecture and optimization decisions across modern transformer-based and hybrid architectures, including both training-time and inference-time performance.
- Lead large-scale training efforts on distributed GPU clusters, including systems operating at the scale of 1,000+ GPUs.
- Define and execute data strategy across data curation, mixture design, deduplication, decontamination, human-in-the-loop pipelines, preference data, evaluation data, synthetic data, and production feedback loops.
- Build and improve evaluation and release-quality systems, including model evals, quality gates, regression detection, release criteria, model-readiness reviews, and post-release monitoring.
- Partner closely with infrastructure and research engineering teams to improve distributed training reliability, checkpointing, fault tolerance, observability, reproducibility, and cost-performance tradeoffs.
- Debug and improve model behavior across the full stack: data, training, post-training, evaluation, infrastructure, product integration, and production feedback.

## What We’re Looking For

- Experience leading, or serving as a principal contributor to, large-scale LLM, multimodal, or foundation-model training or post-training programs.
- Deep experience with transformer-based models, hybrid architectures, modern deep-learning frameworks, and distributed training systems.
- Strong practical experience with post-training and alignment methods such as SFT, RLHF, DPO, GRPO, RLAIF, reward modeling, preference optimization, tool-use fine-tuning, or related approaches.
- Experience operating or partnering on large-scale training infrastructure, ideally including GPU clusters at the scale of 1,000+ GPUs.
- Strong systems instincts around throughput, cost, reliability, observability, debugging, checkpointing, reproducibility, and fault tolerance.
- Excellent judgment around data quality, evaluation design, model regressions, release readiness, and production model behavior.
- Ability to balance research ambition with product pragmatism, user impact, and operational discipline.
- Experience leading senior technical teams while continuing to contribute directly to technical decisions and implementation.
- PhD in Computer Science, Machine Learning, Artificial Intelligence, or a related field, or equivalent practical experience.

Employee Pay Disclosures

At Inflection AI, we aim to attract and retain the best employees and compensate them in a way that appropriately and fairly values their individual contributions to the company. For this role, Inflection AI estimates a starting annual base salary to fall within the range of $400,000 to $550,000, depending on a candidate’s qualifications and level of experience. This role also includes a meaningful equity component, allowing employees to share in the long-term success of the company.

## Benefits

Inflection AI values and supports our team’s mental, emotional, financial and physical health. We are focused on building a positive, safe, inclusive and inspiring place to work. Our benefits include:

- Robust medical, dental and vision options with employer contributions for HSA, FSA and DFSA
- 401k matching program
- Flexible Time Off, 10 paid holidays, 5 days sick leave
- Parental, Medical and Family care leave
- Generous cell-phone, wellness and office set up stipends
- Support of country-specific visa needs for international employees living in the Bay Area

## About Inflection AI

## Company Overview
- **One-liner**: Inflection AI is an AI studio creating human-centered, emotionally intelligent AI models and agents for individuals and enterprises.
- **Entity Type**: Private (Venture-backed; two funding rounds totaling $1.525B)
- **Headquarters**: Palo Alto, California, United States
- **Founded**: 2022
- **Founders**: Reid Hoffman, Mustafa Suleyman, Karén Simonyan

## Core Business
- **Primary industry**: Artificial Intelligence / Machine Learning
- **Target customers**: B2C (Pi chatbot for individuals), B2B (enterprise API and on-premises solutions)
- **Mission**: “Harness the power of AI to improve human well-being and productivity” – structured as a public benefit corporation.

## Products & Services
- **Pi (Personal AI Assistant)**: A voice-enabled chatbot available on iOS, Android, and web, designed to provide high conversational and emotional intelligence. Free for individual users.
- **Inflection API**: Enables enterprises to integrate Inflection’s conversational AI models into their own applications, with fine-tuning and customization options.
- **On-Premises / Private Cloud Solutions**: Deployments for regulated industries (e.g., wealth management) where data must never leave the customer’s network.
- **BoostKPI (acquired)**: A data analysis platform that helps organizations query and make sense of their data using natural language.
- **Jelled.ai (acquired)**: An organizational data tool that connects to email, accounting, and other business systems to provide Socratic dialogue and insights.

## Market Standing
- **Valuation/Market Cap**: Not publicly disclosed
- **Key Metric**: Total funding $1.525 billion (latest round: $1.3B led by Microsoft and Bill Gates, June 2023). Annual revenue estimated at $2.0M (LinkedIn data).
- **Notable Investors/Partners**: Microsoft, Bill Gates, UiPath (partnership), Greylock Partners (talent source)
- **Growth Signals**: 62 employees (+28.8% YoY); “hundreds” of API customers; acquisitions of BoostKPI and Jelled.ai; active research into agentic AI.

## Competitive Advantages
- **Emotional Intelligence (EQ) + IQ**: Models are built on a unique, proprietary dataset collected over two years, giving them industry-leading conversational intelligence.
- **On-Premises / Private Cloud**: Ability to run entirely within a customer’s own infrastructure – critical for regulated industries.
- **Public Benefit Corporation Structure**: Legally committed to societal well-being, which builds trust with customers and partners.
- **Small, Agile Team**: Despite raising over $1.5B, the company remains lean (~62 people), allowing rapid iteration and deep collaboration.

## Strategic Focus
- **Enterprise Pivot**: After Microsoft licensed Inflection’s models and hired co-founders Mustafa Suleyman and Karén Simonyan, CEO Sean White refocused the company on practical enterprise use cases rather than the AGI race.
- **Agentic AI**: Research and development into autonomous agents that act on behalf of users, with a focus on trust and alignment.
- **Data Analysis & Productivity**: Acquisitions of BoostKPI and Jelled.ai accelerate the ability to deliver insights from organizational data.
- **Partnerships**: Collaborations like UiPath to embed conversational intelligence into automation workflows.

## Why Work Here
- **Mission-Driven**: As a public benefit corporation, employees work on AI that aims to improve human well-being – a differentiator from many AI labs.
- **Cutting-Edge Technology**: Opportunity to work on frontier models (mixture-of-experts, state-of-the-art conversational AI) without the scale of a giant tech company.
- **Small Team, High Impact**: With only 62 people, every role has significant ownership and visibility. Engineering makes up 33% of the workforce.
- **Culture of Trust**: Leadership emphasizes transparency and trust, reinforced by the public benefit structure.
- **Compensation & Perks**: Not publicly detailed, but LinkedIn reviews rate the company 5.0/5.0 (2 reviews). Alumni often move to Microsoft AI, Google, and other top AI organizations.
- **Work Policy**: Headquarters in Palo Alto; likely hybrid/office-based (not explicitly stated). Active job postings (2 as of search) include Research Engineer, Voice and Senior Backend Engineer.

## Sources
1. [inflection.ai](https://inflection.ai/)
2. [linkedin.com](https://www.linkedin.com/company/inflectionai)
3. [techbrew.com](https://www.techbrew.com/stories/2025/03/28/inflection-ceo-sean-white)
4. [greenhouse.io](https://job-boards.greenhouse.io/inflectionai)

## Other roles at Inflection AI

- [Director of Product Marketing](https://feeny.ai/job/director-of-product-marketing-inflection-ai-palo-alto-california-6jq8v94frad0) — Palo Alto California, United States
- [Program Lead, Safety, Wellbeing and Regulatory](https://feeny.ai/job/program-lead-safety-wellbeing-and-regulatory-inflection-ai-dublin-2dhk0t1rb0t0) — Dublin, Ireland
- [Principal Engineer, Agentic AI Systems](https://feeny.ai/job/principal-engineer-agentic-ai-systems-inflection-ai-palo-alto-california-wg93yg42rzxf) — Palo Alto California, United States
- [Principal Research & Engineering, Realtime Voice AI](https://feeny.ai/job/principal-research-engineering-realtime-voice-ai-inflection-ai-palo-alto-vbx7kq9h24x7) — Palo Alto California, United States
- [Staff Engineer, Agentic](https://feeny.ai/job/staff-engineer-agentic-inflection-ai-palo-alto-california-smkham3tkvvx) — Palo Alto California, United States