Christopher Greiner
Analyst · Morgan Stanley
Thank you, David. As you said, it was a strong start to the year, indeed, highlighted by an increase in visibility from new customer wins and rapid expansion of existing customers, which is leading to a big step-up in revenue and adjusted EBITDA guidance.
To that end, my remarks today will focus on 2 key topics. First, a run-through of the results with an update on the green shoots we're seeing from several of 2024 growth catalysts, namely, outlining the automotive and insurance verticals return to growth, discussing our progress scaling recently signed large agency holdcos, providing an update on political candidate spending and sharing sales productivity and pipeline conversion metrics with large enterprise customers.
And then I'll close by detailing the increase in our second quarter and full year guidance, along with how our growth drivers are incorporated into the outlook. All right. Let's dive in by starting with the results. In the first quarter, we delivered $195 million in revenue, up 24% year-to-year.
The $8 million of upside versus the midpoint of guidance was broad-based. We ended the quarter with 460 scaled customers, which, as a reminder, accounts for 98% of total Zeta revenue and spend at least $100,000 on a trailing 12-month basis. This was up 8% from 4Q and 49% or 12% from a year ago, at the high end of our 8% to 12% growth model.
Taking into consideration typical 4Q to 1Q seasonality, this was consistent with what we added sequentially last year, but what really stood out was the rate at which customers scaled up. The growth rate of our 1 million-plus super-scaled cohort accelerated 31% year-to-year, an increase from 131 in 4Q '23 to 144 in 1Q 24.
To put this into perspective, the sequential jump of 13 is the highest increase we've ever seen. A couple of data points worth noting on the super scale increase. First, all 13 customers scaled up from the $100,000 to $1 million cohort, a strong demonstration of our land, expand, extend sales model and a good illustration while over 90% of our revenue is generated from customers with us over a year.
And second, while a few of those were agencies, most for large enterprise expansions across a breadth of industries, ranging from technology, consumer and retail and travel and hospitality.
Growth in super scale customer count led to double-digit ARPU growth. Sale customer ARPU in the first quarter grew 11%, an increase from the 7% year-to-year growth in 4Q '23 and at the high end of our 8% to 12% growth model. This was driven by customers using 2 or more channels, which increased over 30% year-to-year.
We also grew our quota carrier count going from 136 at the end of 2023 to 142 at the end of the first quarter with a solid pipeline of candidates entering the second quarter as well. Our established practice of hiring experienced sellers with marketing domain and industry vertical expertise, along with providing comprehensive training curriculum is leading to increasing sales productivity metrics, comparing today's group of less than 12-month tenured sellers to the average of the prior 3 cohorts.
So, going all the way back to 2021, the most recent classes average time to close improved by almost a month or 20% to 4 months. At the same time, our greater than 12-month tenured sellers win rates, signings and pipeline stats, all increase as their tenure gets longer on the platform.
Increasing sales productivity is translating to progress in our 2024 growth catalysts. First, we saw both the automotive and insurance verticals returned to growth in the first quarter, 90 days sooner than we expected. Their combined growth still trailed total Zeta, but we have good visibility to the remainder of the year by virtue of having recently signed contracts and in other cases, progressing new sales opportunities forward in the pipeline.
Our outlook assumes the 2 combined industries growing double digits year-over-year in 2024. Second, we're starting to see the sales pipeline build for political candidate revenue and would anticipate activity picking up later this summer.
As we sit here today, we're not making any changes to our political candidate revenue guidance assumptions of $15 million in 2024 with $2 million in 2Q, $5 million in 3Q and $8 million in 4Q. This is detailed on Slide 18 in the earnings supplemental presentation.
So, all of the guidance increases I'll discuss later exclude incremental political candidate revenue. Third, while we've talked a lot recently about our expansion with agencies, and I'll do so more in a moment, our first quarter's expansion of ARPU and super scale customers was also driven by large enterprise customers.
And fourth, our advancement with large agency holdcos is still in its early stages, but expanding rapidly. We are now working with the 5 largest agency holdcos was so compelling about the opportunity is that this represents dozens of agencies and hundreds to thousands of brands that account for a large portion of enterprise marketing budgets.
Agencies are pivoting to Zeta's platform for several reasons. First, we help them win new business. Zeta's insights and data intelligence identifies new audiences and personas for the agency's clients to target. And Zeta's artificial intelligence recommends intent-driven omnichannel activation strategies, resulting in more efficient and higher ROI campaigns.
Second, we help them offer incremental products like client data enrichment. This enables new cross-selling opportunities for the agency and makes them stickier. And third, we provide deterministic people-based measurement attribution as opposed to cookie based. This allows agencies to drive better outcomes and the ability to prove their ROI attribution to clients.
Each of our agency holdco relationships are at different stages, ranging from 4 years on the platform at a larger scale to those just beginning to ramp. We have good visibility into this dynamic going into 2024, which is why in our last earnings call, we said it was prudent to assume a similar revenue mix and percentage of cost of revenue profile in 2024, as you saw exiting 2023. I think that continues to be a good assumption.
This is because new holdcos on the platform often start with integrated channels, primarily social networks like Facebook, YouTube and others, which have a lower margin profile in the mid-30s. These newer holdcos are also using direct channels, and our plan is to grow their direct channel mix, meaning use of Zeta's CDP, e-mail, demand-side platform and CTV as their spend increases with Zeta.
We're simply early in our partnership selling cycle today as Slide 12 in our earnings supplemental illustrates. With this dynamic in mind, our direct revenue mix in 1Q was 67%. Importantly, the margin profile of our direct revenue continues to hold firm in the mid-70s range.
Overall, Zeta's cost of revenue in the quarter was 39.4%, up 490 basis points year-to-year, but an improvement of 80 basis points quarter-to-quarter, which was slightly better than our expectation of 40%.
Staying on some of our other profit metrics, our first quarter GAAP net loss was $40 million, which includes $53 million of stock-based compensation. Excluding the accelerated expensing related to our IPO, stock-based compensation would have been $39 million.
In 1Q, total OpEx grew only 10% near year, excluding stock-based compensation and is down 570 basis points as a percentage of revenue. Our disciplined expense management and better sales productivity resulted in continued year-over-year adjusted EBITDA margin expansion, our 13th straight quarter of doing so.
In the quarter, we generated $30.5 million of adjusted EBITDA, up 27% year-to-year with 40 basis points of margin expansion to 15.6%. Cash flow from 1Q operating activities was $25 million, up 23% year-on-year, with free cash flow of $15 million, up 51% year-to-year. This brings me to my final topic, our increased 2024 revenue and profit guidance.
With structural forces driving our momentum, the expansion and visibility we have into the sales pipeline and strong productivity of our sellers, we're increasing our revenue and adjusted EBITDA outlook for each quarter in 2024. Details can be found on Slide 17 in our earnings supplemental.
For the full year of 2024, we're increasing the midpoint of revenue guidance to $900 million, representing 24% growth year-over-year. This is a $25 million increase from our prior guidance, well above the $8 million upside we achieved in Q1 and represents an acceleration of full year growth through 2023.
As mentioned earlier, none of the increase is attributable to higher political candidate revenue assumptions. Those remain constant from our prior guidance at $15 million for the full year.
For the second quarter of 2024, we're increasing the midpoint of revenue guidance by $8 million to $212 million, up 23% year-on-year. In terms of adjusted EBITDA, we're increasing the midpoint of 2024 guidance to $171 million, representing a year-over-year increase of 32% or 19% margin.
For the second quarter of 2024, we're increasing the midpoint of adjusted EBITDA guidance by $1.3 million to $35.5 million, up 32% year-to-year or 16.8% margin. We continue to expect full year free cash flow in the range of $75 million to $85 million. We started the year with a wide free cash flow range. And with these increases, we can see scenarios where we start to gravitate to the higher end of the range.
The gating factor here is simply the timing of collections from newer agency customers who, we've discussed previously have longer payment cycles than our enterprise customers.
In summary, there's obviously a lot we're happy about. And with the increased visibility, we feel very good about the increased guidance. Our growth catalysts are showing green shoots. We're seeing encouraging returns on investments across product development, sales and marketing. And we're creating deeper and stickier relationships with our enterprise and new agency customers.
It's good when all those vectors are pointing up. Now, let me hand the call back to the operator for me and David to take your questions. Operator?