Joydeep Goswami
Chief Financial Officer, Chief Strategy & Corporate Development Officer at Illumina
Thank you, Jacob.
I'll start by reviewing our consolidated financial results, followed by segment results for core Illumina and GRAIL and then conclude with my remarks on our current outlook for 2024. I'll be discussing non-GAAP results, which includes stock-based compensation. I encourage you to review the GAAP reconciliation of these non-GAAP measures, which can be found in today's release and in the supplementary data available on our website.
In the fourth quarter, consolidated revenue of $1.12 billion was up 4% year-over-year, both on a reported and constant currency basis. Consolidated revenue was flat from the third quarter of 2023. Non-GAAP net income was $22 million or $0.14 per diluted share, which included dilution from GRAIL's non-GAAP operating loss of $152 million for the quarter. Non-GAAP EPS exceeded our expectations, driven by higher revenue and gross margin and lower operating expense for the quarter.
Our non-GAAP tax rate was 55.4% for the quarter and 41.8% for full year 2023 compared to 29.3% in Q4 2022 and 26% for full year 2022. Although both periods reflect the impact of R&D capitalization requirements, the impact to our effective tax rate in 2023 was more significant due to our lower earnings. In addition, our non-GAAP tax rate for both years include a meaningful impact from the consolidation of GRAIL's losses. Absent the impact of GRAIL, our full year 2023 core tax rate was in the mid-20s. Our non-GAAP weighted average diluted share count for the quarter was approximately $159 million.
Moving to segment results. Core Illumina fourth quarter revenue of $1.1 billion was up 3% year-over-year on both a reported and constant currency basis, and included an anticipated reduction of approximately 5 percentage points from 2 primary categories: one, the decrease in COVID surveillance and the effect of sanctions in Russia that together represented approximately 3 percentage points and two, the year-over-year reduction in China revenue that represented approximately 2 percentage points. Despite these impacts, core Illumina revenue exceeded expectations due to stronger-than-projected NovaSeq X placements an uptake in X consumables with strong early demand for the 25B flow cell that launched in Q4.
Core Illumina sequencing consumables revenue of $687 million was flat year-over-year. Stronger-than-expected NovaSeq X consumables purchases were largely offset by the anticipated reduction in NovaSeq 6000 consumables and the impact of pricing transitions as customers continue to adopt the NovaSeq X. Total sequencing consumables revenue was also impacted by COVID, Russia and China factors that I previously noted as well as the continued impact of macroeconomic conditions on customers' purchasing behavior. COVID surveillance contributed approximately $4 million in total revenue in Q4 2023 compared to $20 million in Q4 2022.
Turning to sequencing activity. Total activity on our connected high and mid-throughput instruments grew 46% year-over-year in the quarter following the 29% year-over-year growth we reported in Q3. Sequentially, Q4 sequencing activity grew 13% from Q3. As a reminder, we believe this data is a useful reference that shows the general activity trends across our installed base and is directionally correlated with revenue over time. Sequencing instruments revenue for core Illumina of $161 million grew 10% year-over-year in Q4, driven primarily by NovaSeq X, which more than offset the decline in NovaSeq 6000 shipments. Growth in high-throughput instruments was partially offset by the expected decline in mid- and low-throughput shipments due to capital purchase and cash flow constraints that continue to impact our customers' purchasing behaviors as well as local competition in China.
For NovaSeq X, we exited Q4 with 390 orders since launch. Our shipments of 79 NovaSeq X instruments in Q4 brought our total installed base to 352 instruments. While we expect most of our NovaSeq 6000 customers to transition to the NovaSeq X over time, we are still very early in this transition. As of the end of 2023, our net installed base for NovaSeq 6000 was approximately 1,770 instruments, which reflects approximately 110 instruments that have been deactivated between 2017 and 2023. The majority of these were in 2023 due to customer transitions to NovaSeq X. We expect this to increase in 2024 as customers continue to ramp up utilization of NovaSeq X.
Additionally, going forward, we will be reporting our annual instrument installed base figures on a net basis, which accounts for instruments that have been decommissioned or inactivated since launch. The information included on this slide includes additional details to help you with your modeling. We will be posting this presentation to our Investor Relations website following our prepared remarks. Core Illumina sequencing service and other revenue of $152 million was up 16% year-over-year, driven primarily by an increase in revenue from strategic partnerships and higher instrument service contract revenue on a growing installed base.
Moving to the rest of core Illumina P&L. Core Illumina non-GAAP gross margin of 64.7% for the quarter decreased 260 basis points year-over-year, primarily driven by the mix of lower-margin strategic partnership revenue, lower instrument margins due to the NovaSeq X launch, which is typical with a new platform introduction and increased field services and installation costs partially offset by lower freight costs. Core Illumina non-GAAP operating expenses of $507 million were down $21 million year-over-year, primarily due to continued expense reduction initiatives and lower performance-based stock compensation expense year-over-year. As a result of these factors and higher revenue, core Illumina non-GAAP operating margin was 18.5% in Q4 2023 compared to 17.8% in Q4 2022.
Transitioning to financial results for GRAIL. GRAIL revenue of $30 million for the quarter grew 30% year-over-year, driven primarily by adoption of Galleri. GRAIL non-GAAP operating expenses totaled $167 million and increased $1 million year-over-year.
Moving to consolidated cash flow and balance sheet items for the quarter. Cash flow provided by operations was $224 million. Capital expenditures were $51 million and free cash flow was $173 million. We did not repurchase any common stock. We ended the quarter with approximately $1.05 billion in cash, cash equivalents and short-term investments.
Moving now to 2024 guidance. As Illumina continues to move as quickly as possible to resolve GRAIL, given the uncertainty around the specific timing and impact of the GRAIL divestment, the company is focusing its 2024 financial outlook on core alumina. Our guidance does not assume any impact for the potential divestment of GRAIL in 2024. Upon the completion of the divestment, we will provide non-GAAP EPS guidance for the full year 2024. As Jacob mentioned, our outlook assumes the current challenging macroeconomic environment persists in 2024 and tighter funding and budget pressures continue to impact our customers' purchasing decisions. We expect full year 2024 core revenue to be approximately flat from 2023, reflecting the following offsetting factors.
We expect core Illumina sequencing instrument revenue to decline in the high teens year-over-year driven primarily by a decrease in NovaSeq X instrument placements. The reduction reflects the expected transition in our adoption curve to early majority customers from early adopters and the lower backlog entering 2024 compared to 2023. We also expect capital and cash flow constraints to continue to impact purchasing behavior and moderate instrument placements in 2024. We expect core Illumina sequencing consumables revenue to grow in the low single digits year-over-year, driven primarily by modest growth in high throughput consumables, as increased NovaSeq X consumables purchases and sequencing volume outpaced the expected decline in NovaSeq 6000 consumables and the impact of pricing transitions.
Moving to annual pull-through. Going forward, we will be calculating and providing pull-through figures based on the instruments net installed base. As I mentioned previously, supplemental information is included in our earnings presentation to help with modeling, which will be posted to our Investor Relations website following our prepared remarks. Importantly, this does not change reported revenue in any way. We expect annual pull-through for NovaSeq 6000 of approximately $700,000 to $800,000 per system in 2024, as customers continue to transition sequencing volume to NovaSeq X. We expect annual pull-through for NextSeq 1K/2K in the range of $80,000 to $130,000 per system in 2024, which primarily reflects the impact of customers transitioning to X lead chemistry as it becomes available on NextSeq 1K/2K. We expect annual pull-through for MiSeq in the range of $30,000 to $40,000. We expect the remainder of our pull-through ranges to be in line with historical guidance.
We expect core Illumina total sequencing revenue to be approximately flat year-over-year. This includes intercompany sales to GRAIL of approximately $30 million, which are eliminated in consolidation. We expect core Illumina non-GAAP operating margin of approximately 20%. Our operating margin expectations reflect the benefit of our continued gross margin improvement and expense reduction initiatives offset by normalization of our performance-based compensation as well as the impact of inflation and market-based merit increases. For the first quarter of 2024, we expect core Illumina revenue in the range of $1.03 billion to $1.04 billion, reflecting a year-over-year decrease of 3.5% to 4.5%, driven predominantly by the following factors. We expect lower NovaSeq X instrument shipments year-over-year, given that we are entering 2024 with a more modest backlog compared to the significant pre-order book we entered 2023 following the launch of NovaSeq X.
We expect the increase in NovaSeq X consumables purchases year-over-year to be largely offset by the anticipated reduction in NovaSeq 6000 consumables and the impact of pricing transitions consistent with the trend we saw in Q4. We expect an increase in sequencing service and other revenue year-over-year driven by strategic partnership initiatives and higher instrument service contract revenue on a growing installed base. For the first quarter, we expect core Illumina non-GAAP operating margin of approximately 18%. Lastly, for the first quarter, we expect core Illumina non-GAAP net other expense of approximately $12 million with the year-over-year increase driven primarily by lower interest income on our lower cash balance following the repayment of our convertible notes in mid-2023.
I will now turn it back over to Jacob for his closing remarks. Thank you.