The phrase "AI Engineer" started appearing in job boards around late 2023. By mid-2024 it had become one of the most-searched job titles in tech. By early 2025, it's also one of the most inconsistently defined — which means if you're targeting this role, you need to understand exactly what each employer means by it before you apply.
We spent six weeks talking to hiring managers, engineering leads, and recruiters at 12 UK technology companies — from Series A startups to FTSE 250 businesses deploying AI at scale. What we found surprised us.
Three very different things people call "AI Engineer"
The title "AI Engineer" maps to at least three distinct role types in the UK market right now. Applying without understanding which one you're interviewing for is one of the most common and costly mistakes candidates make.
Type 1: The LLM Application Builder
This is the most common type in early-stage startups and product companies. The core job: build applications on top of foundation models using APIs. Think LangChain, LlamaIndex, OpenAI API, Anthropic API. The work is primarily software engineering — you're building RAG pipelines, prompt management systems, evaluation frameworks, and production API integrations.
What they actually test for: Python fluency, REST API design, basic understanding of embeddings and vector databases, and software engineering practices (testing, CI/CD, observability). Deep ML knowledge is explicitly not required at most of these companies.
Type 2: The Fine-Tuning and Adaptation Specialist
Found more commonly at companies building proprietary models or heavily customising open-source ones. This role requires genuine ML engineering skills: understanding of training loops, PEFT methods (LoRA, QLoRA), evaluation pipelines, and the infrastructure to run GPU workloads at scale.
What they actually test for: Hands-on PyTorch experience, familiarity with HuggingFace ecosystem, ability to design and run training experiments, and understanding of compute cost optimisation.
Type 3: The ML Platform / MLOps Hybrid
A more infrastructure-flavoured role that has emerged as companies mature their ML operations. These engineers build the platforms, tooling, and infrastructure that allow other engineers to work efficiently with AI systems.
What skills actually matter in 2025
Across all 12 interviews, some skills appeared consistently regardless of role type. These are the genuine non-negotiables.
| Skill | Frequency mentioned | Tested in interview? |
|---|---|---|
| Python (intermediate to advanced) | 12/12 | Yes — always |
| LLM API integration (OpenAI, Anthropic, etc.) | 11/12 | Yes — take-home or live |
| Prompt engineering & evaluation | 10/12 | Often — design a prompt or eval framework |
| Vector databases (Pinecone, FAISS, Weaviate) | 9/12 | Conceptual — rarely hands-on tested |
| RAG pipeline design | 9/12 | Yes — system design question |
| Observability & monitoring for AI | 8/12 | Rarely tested — but discussed |
| PyTorch / model training | 6/12 | Only for Type 2 roles |
| HuggingFace ecosystem | 7/12 | Yes, for fine-tuning roles |
The portfolio that actually gets interviews
Across all conversations, one theme recurred strongly: hiring managers are exhausted by portfolios full of Jupyter notebooks that run on the Titanic dataset. What moves the needle in 2025 is demonstrably different.
Specifically, the three portfolio signals that consistently impressed hiring managers in our conversations were: (1) a demo that actually works and handles edge cases gracefully, (2) documented evaluation methodology showing you know how to measure whether your AI system is working, and (3) evidence of iteration — showing what you tried, what failed, and why.
Salary reality check
Based on our salary survey data from 400 US engineers combined with what hiring managers shared with us, here are honest salary ranges for AI Engineer roles across the US in 2025:
| Level | Base salary range | With equity |
|---|---|---|
| Junior AI Engineer (0–2 yrs) | $70,000 – $90,000 | +$6–19k typical RSU |
| Mid-level (2–5 yrs) | $95,000 – $120,000 | +$13–38k typical RSU |
| Senior (5+ yrs) | $125,000 – $185,000 | +$25–100k RSU |
| Staff / Principal | $175,000 – $230,000+ | Significant equity |
What to do next
If you're targeting AI Engineer roles in 2025, here's the most direct path based on everything we've learned:
First: Figure out which type of AI Engineer role you're targeting (Type 1, 2, or 3 as above) based on the companies you want to work at. Read 10 actual job descriptions carefully. The required tech stack will tell you everything.
Second: Build one portfolio project that is deployed and demonstrably works. A RAG system over your own documents, hosted publicly, with an evaluation dashboard, will beat 50 Kaggle notebooks every time.
Third: Understand the evaluation pipeline. The biggest gap between strong and weak AI Engineer candidates right now is the ability to measure whether your AI system is actually working — not just build it.