Interim, fractional, or as-a-service CTO: a neutral comparison

A portfolio company that has lost its engineering leader, or never had one, has four ways to fill the gap. Each supplies something different, and the comparison is easier once the four are described plainly.

An interim CTO is a full-time executive engaged for a fixed period, usually until a permanent hire starts. A fractional CTO is a part-time executive who works a fixed number of days per week or month and serves other companies in the rest of the time. A permanent hire is the long-term answer, found through a search that takes months. An as-a-service model is a partner that supplies engineering leadership and delivery capacity together and is contractually accountable for the outcome rather than for hours.

The shorter comparison of one of these against a build partner is on our comparison page with a fractional CTO. This page compares all four.

What does each option supply?

Each option supplies a different mix of judgement, direction, building capacity and accountability, and the table is the fastest way to see it.

Option	Supplies	Does not supply	Typical duration	Accountable for
Interim CTO	Full-time judgement, direction, hiring, board reporting	Building capacity beyond the existing team	Three to twelve months, until a permanent hire	Running the function during the period
Fractional CTO	Part-time judgement and direction; board reporting	Daily presence; building capacity	Open-ended, one to three days a week	Advice and direction on the days engaged
Permanent hire	Everything an executive supplies, indefinitely	Nothing, once found; the search itself takes months	Years	The function, the team, the outcome
As-a-service (build partner)	Leadership plus a delivery team; the specification, the build, and the evaluation of it	A person on the org chart as CTO	Scoped per engagement, with a handover	The delivered outcome, by contract

Two things in the table decide most cases. First, neither an interim nor a fractional executive supplies building capacity: both direct the team that exists. A company whose value creation plan needs software built has to arrange the building separately, whichever executive it chooses. Second, accountability differs in kind. An executive is accountable as an employee or contractor; a partner is accountable by contract for a named outcome. Which one the fund prefers depends on where it wants the delivery risk to sit.

Reveneau's forward deployed model is the as-a-service row: engineers placed with the portfolio company who take a fixed scope, write the code with AI, prove each change against an evaluation suite written from the specification, and hand the running system over with the team able to operate it. It is one of four options and it fits some situations and not others, as the rest of this page sets out. The pillar guide to technology after the deal sets engineering leadership among the capability decisions in the second month after closing.

How long will the gap last?

The duration of the gap is the first question, because it rules options in and out before cost is considered.

A gap of under three months, with a permanent search already running, is an interim gap. An interim executive starts within weeks, runs the function, and leaves when the hire starts. A fractional executive fits a company whose engineering function is small enough that full-time leadership would be idle for half the week, and whose gap has no planned end. A permanent hire is the answer when the company will need a full-time engineering leader for the rest of the hold, which is most companies past a certain size; the search is the cost.

The U.S. Bureau of Labor Statistics projects 16 percent employment growth for computer and information systems managers from 2025 to 2035, described as much faster than the average across occupations, with 53,500 openings projected each year on average over the decade. A permanent search is competing in that market, and the interim option exists because the search takes as long as it takes.

The as-a-service option is scoped by work rather than by time: it lasts as long as the build it is engaged for, and it ends with a handover. It suits a gap that coincides with a defined build (the shared layer for a buy-and-build platform, a carve-out separation, a first-year plan with a long findings backlog) and suits an open-ended leadership gap less well.

How much building is needed?

The amount of building needed is the second question, and it is the one that most often changes the answer.

If the value creation plan is mostly about running the existing product well, an executive is the whole answer. If the plan needs a product rebuilt, a platform integrated, or an AI capability shipped, an executive directs and somebody builds. The building capacity comes from the existing team, from hiring, or from a partner, and each has a cost the scaling engineering teams guide sets out. Brooks's law, from Fred Brooks's 1975 book The Mythical Man-Month, is the caution on hiring into a build that is already late: adding people to a late software project makes it later.

FTI Consulting's 2026 Private Equity AI Radar, published 19 May 2026 from a survey of 200 fund and operating leaders, found talent to be the primary constraint on scaling AI adoption, cited by 35 percent of respondents. A constraint that is talent is one an executive alone does not remove, and it is the case in which the as-a-service row of the table is built to fit, since it brings the builders with the leadership.

Who should carry the delivery risk?

The delivery risk sits with whoever is accountable when the build is late or wrong, and the four options place it differently.

With an interim or fractional executive, the risk sits with the company. The executive directs; if the build is late, the company has a late build and an executive's explanation. With a permanent hire, the same is true, with a longer horizon. With an as-a-service partner, the risk sits with the partner by contract, provided the contract names the outcome and its evaluation rather than a number of hours. The technical due diligence guide describes how a fund verifies a codebase; the same evaluation suite that verifies it after the fact can be written before the build and used as the contract's definition of done.

Where the fund wants the risk depends on the fund. A fund with a strong operating group and a portfolio CTO bench may prefer to hold it. A fund with one operating partner across twelve companies may prefer to place it. Both are reasonable, and the choice should be written down as the reason for the option chosen.

What does each option cost against a permanent hire?

Each option is priced against the permanent hire, and the benchmark for that is public. The U.S. Bureau of Labor Statistics reports a median annual wage of $175,140 for computer and information systems managers in May 2025. A CTO at a funded company is paid above that median, with equity on top, and the figure is the floor rather than the market rate for the role.

Against that floor:

• An interim executive is usually priced per day or per month at a rate above the permanent equivalent, because the engagement is short and the executive carries the gaps between engagements. The total depends on the duration, which is why the first question comes first.
• A fractional executive is priced per day at a similar or higher day rate, for fewer days, so the annual total is lower than a permanent hire while the daily cost is not.
• A permanent hire costs the salary, the equity, the benefits, and the search, plus the months of gap while the search runs.
• An as-a-service partner is priced per scope rather than per person. The number of people supplying the scope is the partner's decision, which is where a partner that writes its code with AI and needs fewer engineers per build passes the saving into the price, as a mechanism rather than a percentage.

No third party has published a comparison of those four prices, and any figure offered for one without the vendor's name and the date is a guess. Ask each vendor for a written price against a written scope and compare them on the same scope.

What should the engagement include, whichever option is chosen?

Whichever option is chosen, four things should be written into it.

1. A review date. Every option, including the permanent hire, gets a date on which the board asks whether it is working.
2. Board reporting in a fixed format, so the option can be judged on the same four delivery measures every quarter. Reporting engineering progress to the fund gives the format.
3. Knowledge transfer with a test. BCG's survey of 100 senior private equity investors, published 7 January 2026, found that among the firms it classed as successful, 70 percent use specialised digital boutiques and only 45 percent systematically ensure knowledge transfer from external partners to internal teams. An interim, a fractional and a partner all leave; the company's team has to be able to run the result on the day they do.
4. A handover plan, which for an interim is the permanent hire's start, for a fractional is a decision point on whether to convert to permanent, and for a partner is the date the internal team runs the system unaided.

The technology workstream in a 100-day plan places this decision in days 31 to 60 after closing. If the as-a-service row is the one that fits, building with investors and their portfolio companies describes how we take on that engagement.