Quick answer
After a Series A, an agency gives speed and specialist skill while you learn what works, and an in-house team gives control and depth once the playbook is clear. Many companies use a hybrid: an in-house lead for strategy and an agency for execution, then bring work in-house as volume proves it.
The Series A is closed. The board expects growth. The temptation is to hire quickly: a head of growth, a few marketers, perhaps a sales team.
That can be right, and it can be costly. Here is how to think about post-Series A growth, and the choice between an agency and an in-house team.
What does post-Series A growth need?
Three things: a clear buyer, a repeatable way to reach them and a way to measure what works. Many companies reach a Series A on a strong product and a handful of founder-led sales. The next stage is turning those wins into a system.
Paul Graham’s essay Startup = Growth argues that growth is what defines a startup. The task now is to make growth predictable enough to plan around.
What does an agency give you?
Speed and range. An agency can start in weeks, bring specialists in outbound, paid media, content and analytics, and run tests across channels while you learn. It also brings experience from other companies, which can help you avoid common mistakes.
The trade-offs are shared attention and less depth in your product. A good agency works with you to learn your buyer, but it will never know the product as well as your team.
What does an in-house team give you?
Control and depth. Employees live with the product, sit beside sales and product teams and build long-term knowledge. Over time they can move faster on decisions that need context.
The costs are time and risk. Recruiting takes months, new hires need time to ramp and a wrong hire is expensive. Teams also need management, tools and a clear plan, which a young company may not yet have.
How do they compare?
| Agency | In-house team | |
|---|---|---|
| Speed to start | Weeks | Months |
| Range of skills | Broad | Depends on hires |
| Product knowledge | Learned over time | Deep |
| Cost shape | Fees, flexible | Salaries, fixed |
| Control | Shared | High |
| Risk if wrong | Shorter commitment | Hiring and exit costs |
Neither is better in general. The right choice depends on where you are in the learning curve.
Post-Series A: when does an agency make the most sense?
When you are still learning which channels work. An agency can run controlled tests, report in pipeline terms and show you where to invest. It also suits specialist work that does not need a full-time person, such as deliverability, paid media set-up or analytics.
Gartner’s research on the B2B buying journey describes how complex modern buying has become, with many people and steps involved. A team that can test messages and channels quickly helps you learn how your buyers move through that journey.
When does an in-house team make the most sense?
When the playbook is clear and volume is high enough to keep people busy. If you can describe the buyer, the message, the steps and the numbers, a team can run it and improve it. Core roles, such as a head of growth and a sales lead, usually belong in-house.
Hire for roles you will need for years, and rent expertise for work that changes often.
Why is a hybrid often the practical answer?
Because it matches the risk to the stage. An in-house lead owns strategy, priorities and the relationship with sales. An agency runs execution: outbound, paid tests, landing pages and reporting. As results come in, you move parts in-house, such as SDRs or content, and keep the agency for specialist tasks.
To make a hybrid work, insist on ownership of accounts, data and assets, a documented playbook and a clear plan for handover. Read our guide to outbound agencies vs hiring SDRs for a concrete example.
How should you measure either choice?
Use the same numbers for both: qualified meetings, pipeline created, cost per qualified meeting, win rate, sales cycle length and customer acquisition cost. Google explains in About offline conversion imports how closed deals can be fed back into ad accounts, so campaigns learn from revenue.
Speed also shows up in results. The Harvard Business Review study The Short Life of Online Sales Leads found that firms who replied to leads within an hour were far more likely to qualify them than firms who waited. A growth team of any kind needs fast follow-up.
What do investors want to see?
Honesty and clarity. They want to see that you know your buyer, that you test channels with discipline and that you can explain what spend produces what pipeline. Our guide on what investors want to see in your GTM numbers lists the metrics.
Be careful with claims. The FTC’s advertising basics say that claims must be truthful and supported, which applies to what you say to customers, and it is a good habit for what you tell the board.
What mistakes do Series A companies make?
Hiring a senior leader before the playbook is clear, so that the person invents one from scratch. Splitting budget across too many channels. Letting an agency run without a clear owner inside. Measuring activity instead of pipeline. And failing to document what is learned, so that knowledge leaves with people.
Avoid them by keeping tests small, naming one owner for growth, and holding a monthly review where the numbers and the learning are shared with the whole leadership team.
What does a sensible first six months look like?
In the first month, align on the buyer and the plan, and set up tracking. In months two and three, run two or three channel tests with an agency or a small team, and review results weekly. In months four to six, scale what works, write the playbook and decide what to bring in-house. At each step, keep a learning log, and share it with the board.
Think of the period as building a machine, not just buying results. A machine you understand and own is worth far more than a set of campaigns you cannot explain.
What should you do first?
Write down what you know: your strongest customers, your channels so far and your numbers. Decide what you still need to learn. Choose a structure that fits: an agency to test, a lead to own strategy or a mix. Set a three-month checkpoint, and decide in advance what result will change the plan.
For related reading, see what a GTM agency actually does, your first 90 days after a seed round and our page for funded startups and YC companies. See also our go-to-market strategy service, or book a free go-to-market diagnostic.
How Omega helps funded startups and yc companies
Omega Growth helps funded startups turn a raise into a repeatable pipeline. We start from your strongest early customers, choose one or two channels, run controlled tests and report in pipeline terms, so the next sales hire inherits a system and not a guess.
See how Omega works with funded startups and yc companies · Go-to-market strategy
Frequently asked questions
When should a Series A company hire its first growth team?
When you have a repeatable motion, a clear buyer and enough volume to keep a team busy. Before that, an agency or small specialist support can run tests while you learn. Hire when the playbook can be written down and handed over.
What are the risks of building a growth team too early?
You pay salaries before you know what works, and people may leave before the playbook is clear. A new head of growth also needs time to ramp. Tests run by a small team or an agency reduce the cost of learning.
How do we keep knowledge when working with an agency?
Own the accounts, data and assets, ask for documented playbooks and hold regular reviews with your team. Agree in the contract how handover works. That way you can bring work in-house without starting from scratch.
What should investors expect from our growth plan?
A clear buyer, tested channels, tracked metrics and honest learning. Investors usually want to see how spend turns into pipeline and how that improves over time. Prepare a simple dashboard and a short learning log.
Can an agency replace a head of growth?
Rarely. An agency executes and advises, but a company still needs someone accountable for strategy and priorities inside. A fractional or in-house lead working with an agency often works well.
Sources
- Paul Graham, Startup = Growth, accessed 2026.
- Gartner, The B2B Buying Journey: Key Stages and How to Optimize Them, accessed 2026.
- Google Ads Help, About offline conversion imports, accessed 2026.
- Harvard Business Review, The Short Life of Online Sales Leads, 2011.
- Federal Trade Commission, Advertising and Marketing Basics, accessed 2026.