Total revenues were up 6%, with each of our business segments, research, conferences, and consulting, exceeding our expectations.
For Q1, GTS contract value grew 5%.
First quarter new business was up 21% as a result of new logos and upsell with existing clients.
Client engagement continue to be strong, with content and analyst interaction volumes up to 26% compared to Q 2020.
GBS achieved contract value growth of 12%, its first quarter of double-digit growth.
New business growth was a very strong 87% in the quarter.
Our Consulting segment also exceeded our expectations, with bookings up 26% during Q1.
Free cash flow for the quarter was $145 million, up significantly versus the prior year.
In addition, we used that cash flow plus cash balances to purchase more than $600 million in stock through April of this year.
With these repurchases, our Board increased our share repurchase authorization by another $500 million.
First quarter revenue was $1.1 billion, up 8% year-over-year as reported and 6% FX-neutral.
In addition, total contribution margin was 70%, up more than 320 basis points versus the prior year.
EBITDA was $320 million, up 50% year-over-year and up 44% FX-neutral.
Adjusted earnings per share was $2, and free cash flow in the quarter was $145 million.
Research revenue in the first quarter grew 8% year-over-year as reported and 6% on an FX-neutral basis, and we saw strong retention and new business throughout the quarter.
First quarter research contribution margin was 74%, up about 200 basis points versus 2020.
Total contract value grew 6% FX-neutral to $3.7 billion at March 31.
Quarterly net contract value increase, or NCVI, was $59 million, significantly better than the pandemic affected first quarter last year.
Global Technology Sales contract value at the end of the first quarter was $3 billion, up 5% versus the prior year.
GTS CV increased $34 million from the fourth quarter.
By industry, CV growth was led by technology, healthcare and services, while retention for GTS was 98% for the quarter, down about 560 basis points year-over-year.
GTS new business was up 21% versus last year with strength in new logos and an improvement in upsell with existing clients.
Global Business Sales contract value was $731 million at the end of the first quarter, up 12% year-over-year.
GBS CV increased $25 million from the fourth quarter.
While retention for GBS was 104% for the quarter, up more than 330 basis points year-over-year, GBS new business was up 87% over last year, led by very strong growth across the full portfolio.
Conferences revenue for the quarter was $25 million.
We had about $10 million of onetime revenue in the quarter.
Contribution margin in the quarter was 56%.
First quarter consulting revenues increased by 4% year-over-year to $100 million.
Consulting contribution margin was 39% in the first quarter, up 860 basis points versus the prior year quarter.
Labor-based revenues were $84 million, up 4% versus Q1 of last year and down 1% on an FX-neutral basis.
Labor-based billable headcount of 744 was down 8% due to headcount actions taken in Q2 and Q3 of last year.
Utilization was 68%, up about 550 basis points year-over-year.
Backlog at March 31 was $116 million, up 3% year-over-year on an FX-neutral basis after a strong bookings quarter.
Our Contract Optimization business was up 6% on a reported basis versus the prior year quarter and 3% FX-neutral.
Consolidated cost of services decreased 2% year-over-year and 4% FX-neutral in the first quarter.
SG&A decreased 2% year-over-year and 4% FX-neutral in the first quarter as well.
EBITDA for the first quarter was $320 million, up 50% year-over-year on a reported basis and up 44% FX-neutral.
Depreciation in the quarter was up about $3 million versus 2020, including real estate and software, which went into service since the first quarter of last year.
Net interest expense, excluding deferred financing costs in the quarter, was $25 million, flat versus the first quarter of 2020.
The Q1 adjusted tax rate, which we used for the calculation of adjusted net income, was 23.5% for the quarter.
The tax rate for the items used to adjust net income was 22.4% in the quarter.
Adjusted earnings per share in Q1 was $2.
Recall that about $6 million of equity compensation expense, which we normally would have incurred in the fourth quarter of 2020, shifted into the first quarter of 2021.
The weighted average fully diluted share count for the first quarter was 89.1 million shares.
The ending fully diluted share count at March 31st was 87.7 million shares.
Operating cash flow for the quarter was $157 million compared to $56 million last year.
capex for the quarter was $13 million, down 49% year-over-year.
Free cash flow for the quarter was $145 million, which was up about 360% versus the prior year.
Free cash flow as a percent of revenue or free cash flow margin was 22% on a rolling 4-quarter basis, continuing the improvement we've been making over the past few years.
At the end of the first quarter, we had $446 million of cash.
Our March 31st debt balance was $2 billion.
At the end of the first quarter, we had about $1 billion of revolver capacity.
Our reported gross debt to trailing 12-month EBITDA was about 2.2 times.
During the first quarter, we repurchased $398 million in stock at an average price of about $180 per share.
In the month of April, we repurchased more than $200 million of our stock.
At the end of April, the Board increased our share repurchase authorization for the second time this year, adding another $500 million.
As of April 30, we have around $790 million available for open market repurchases.
As you know, travel expenses were close to 0 from April 2020 through March 2021.
For our revenue guidance, we now expect Research revenue of at least $3.935 billion, which is growth of at least 9.2%.
We expect Conferences revenue of at least $170 million which is growth of at least 42%.
We now expect consulting revenue of at least $400 million, which is growth of at least 6.4%.
The result is an outlook for consolidated revenue of at least $4.5 billion, which is growth of 9.9%.
Based on current foreign exchange rates and business mix, the consolidated growth includes an FX benefit of about 200 basis points.
We now expect full year adjusted EBITDA of at least $1 billion, which is an increase of about 22.3% versus 2020 and reported margins of at least 22%.
The 18% to 19% expected margins in the back half of the year should provide a reasonable run rate for thinking about the margins going forward as we will have more fully restored costs and resumed growth hiring.
We expect our full year 2021 adjusted net interest expense to be $102 million.
We expect an adjusted tax rate of around 22% for 2021.
We now expect 2021 adjusted earnings per share of at least $6.25.
For 2021, we now expect free cash flow of at least $850 million.
Finally, we expect to deliver at least $270 million of EBITDA in Q2 of 2021.
With 12% to 16% research CV growth, we will deliver double-digit revenue growth.
With gross margin expansion, sales cost growing in line with CV growth over time and G&A leverage, we can modestly expand margins from a normalized 2021 level of around 18% to 19%.
We repurchased more than $600 million worth of stock this year through the end of April and remain committed to returning excess capital to our shareholders.

Summary:
With these repurchases, our Board increased our share repurchase authorization by another $500 million.
First quarter revenue was $1.1 billion, up 8% year-over-year as reported and 6% FX-neutral.
At the end of April, the Board increased our share repurchase authorization for the second time this year, adding another $500 million.