The Hire You Cannot Justify Yet
If you run a Series B or C company, you probably have this conversation on the leadership team every quarter. AI is becoming central to how every function operates. The CEO wants a plan. The CTO is already stretched. The board keeps asking what the AI strategy is. Somebody senior needs to own it.
The natural answer is "hire a Head of AI." The problem is that at Series B or C, a senior full-time AI leader is a £250k plus hire who will take six to nine months to source, three to six months to ramp, and whose mandate is unclear until they are in the seat.
Most companies in that position do not need a full-time Head of AI yet. They need senior AI judgement, a coherent roadmap, and somebody who can ship production systems while the internal team builds up. That is what a Fractional Head of AI is for.
What a Fractional Head of AI Actually Does
Four responsibilities, one senior owner.
AI strategy
A coherent plan mapped to board-level KPIs, not a list of tools. Most AI strategies we see at growth-stage companies are tool-shaped: "we will use ChatGPT for marketing, Claude for product, Copilot for engineering." That is not a strategy, it is a procurement list.
A real strategy starts from the business: which three to five business processes would, if automated or accelerated by AI, move the metrics the board cares about? Then: what does the technical approach look like, what does the sequencing look like, and what is the 12 month plan? This is the output the board wants to see.
Architecture and stack
The fastest way to burn money in the first 12 months of an AI build is to pick the wrong stack. Most growth-stage companies default to whatever their CTO used at their last company, or whatever the first vendor pitched well. Both are often wrong.
A Fractional Head of AI picks the stack based on the actual use cases: n8n or a similar platform for orchestration, the right frontier model for each job (not one model for everything), vector stores where they matter, boring SaaS where they do not. The goal is to avoid the expensive rebuild 18 months in.
Hiring and mentoring
The point of fractional is to make yourself redundant. A good Fractional Head of AI writes the JD for the full-time successor, sits on interview panels, onboards the new hire, and transitions the ownership cleanly. While that is happening, they mentor internal AI engineers, data scientists, and the heads of function who are building AI into their own teams.
The output is not "we have a Head of AI for two days a week." The output is "in 12 months we have a full-time Head of AI who is effective on day one because the foundations are laid."
Hands-on delivery
Strategy without shipped output is worth nothing. A Fractional Head of AI also builds. Customer support agents, document pipelines, internal tools, finance automation. The mix of strategy and delivery is what makes fractional different from advisory: you get real production systems, not just a monthly update.
At Healf, the #1 company on the Sifted 100 UK & Ireland 2026, this approach has driven 85% daily AI tool adoption across the company. Not because somebody advised on it, but because somebody built it and the team started using it.
When Fractional Beats Full-Time
Three conditions typically point to fractional.
Stage: Series B to D. If AI is important to the business but not the core product, and the company is 50 to 300 people, a Fractional Head of AI is usually the right shape. Once AI is central to the product itself, or the company is past 300 people, the scope justifies full-time.
Budget: cannot yet justify £250k plus full-time. A fractional arrangement is typically 1 to 2 days a week, priced against the output, not the full-time equivalent. You get senior judgement at a fraction of the full-time cost.
Speed: need momentum in the next 90 days. Hiring a Head of AI takes six to nine months minimum. If the board wants a plan and early output in the next quarter, fractional is the only option that delivers both.
When Full-Time Is Right
Stage: Series D plus or pre-IPO. AI is central to the product and the company is big enough to justify full-time scope.
Core AI product. If your product itself is AI, the Head of AI is effectively a co-founder-level hire. Fractional does not work.
Confidence in the spec. If the exec team already knows exactly what the full-time Head of AI should do, the hire is easier and the ROI on a search process is clear.
When Interim Makes Sense
Occasionally the right shape is interim: a full-time senior AI leader for 6 to 12 months while you search. This fits when AI is genuinely full-time in scope already, but the permanent hire will take time to source and you need continuous senior ownership in the interim.
Interim is more expensive than fractional, because it is full-time, and the person is usually a specialist in stepping into established functions rather than building them from scratch. Most growth-stage companies do not need this shape.
How to Structure a Fractional Engagement
The engagement models that work:
1 to 2 days a week, minimum quarterly commitment, paid monthly. The quarterly minimum matters because real output takes a quarter to materialise, and shorter commitments attract advisory work rather than delivery work. Fee is usually 30 to 50% of the equivalent full-time cost, benchmarked against output rather than hours.
The alternative that does not work: an hourly advisory arrangement with no minimum. That produces slide decks, not shipped systems.
Next Steps
If you are a CEO or CTO weighing fractional versus full-time for AI leadership, we can walk through the specifics on a 30 minute call. Book a call, or read more at /fractional-ai-lead.