AI clusters have pushed optical interconnects into a new phase. As GPU counts climb into the tens of thousands, the network has to move more traffic in shorter windows with less tolerance for latency, heat, and cable sprawl. Pluggable optics still carry that traffic, but the density and cooling demands of hyperscale AI fabrics are starting to outrun what air-cooled form factors can handle. XPO is the industry's first serious answer to that wall, introduced by Arista and a multi-vendor group at OFC 2026 in March 2026.
What Are XPO Transceivers?
XPO (eXtra-dense Pluggable Optics) is a liquid-cooled, high-density pluggable optical module built for AI-scale networks. Each module delivers 12.8 Tbps and packs an integrated cold plate, so a single rack unit can expose 204.8 Tbps of front-panel bandwidth, roughly four times the density of 1600G-OSFP. It does not replace OSFP across the board, and it is not co-packaged optics (CPO): XPO keeps the module field-replaceable from the front panel while solving density and thermal limits. It is also brand new, defined by a multi-source agreement (MSA) that launched in March 2026, so it is something to plan around rather than deploy today.
Why AI Data Centers Need a New Pluggable Optics Form Factor
Faster links alone do not solve the AI networking problem; you also need more links in the same physical space. The lineage of pluggable form factors, from QSFP through QSFP-DD to OSFP, has been about packing more lanes into a serviceable module, and if you want a refresher on where the current generation sits, this QSFP-DD technical overview covers the eight-lane design that 400G and 800G optics rely on today. XPO is the next step when even that runs out of room.
Why Front-Panel Density Became a Hard Limit
As switch ASIC capacity grows, the front panel turns into the bottleneck. If every optics generation needs more ports, more faceplate area, more cables, and more racks, the network footprint grows faster than the compute it serves. OSFP has been hugely successful and is not going away, but at AI scale its bandwidth per rack unit, cooling headroom, and reliability budget are all under pressure. XPO answers that by lifting bandwidth per module and per rack unit at the same time.
Why XPO Uses Liquid Cooling
At higher speeds, more lanes, faster signaling, and dense photonic integration all dump more heat into the module. Beyond a point, air-cooling fans burn more power moving heat than the networking silicon itself consumes, which is the wall AI operators have been hitting at 800G and 1.6T. XPO is built liquid-first, with the cold plate inside the module rather than bolted on as an afterthought. That alignment matters because large AI data centers are already moving their compute racks to liquid cooling, and the switches in those rooms need to follow.
Why Pluggability Still Matters Compared With CPO
CPO shortens the electrical path by placing optics next to the switching ASIC, but it changes the maintenance model. Once optics are integrated into the package, repair, replacement, and upgrades all get harder. That is not a small concern at AI scale: as Network World reports, a single module failure inside a fabric of 50,000-plus optical links can stall a multi-million-dollar training job, and OSFP, with over 100 million modules projected to ship this year, remains the most widely deployed form factor by a wide margin. XPO keeps the field-replaceable model operators already depend on, which is the whole point of staying pluggable.
Key XPO Specifications
| Specification | What it means for AI data centers |
|---|---|
| 12.8 Tbps per module | One module aggregates roughly eight times the bandwidth of an OSFP module. |
| 64 electrical lanes at 200 Gbps | High lane count and 200G-per-lane signaling combine to reach 12.8T per module. |
| 204.8 Tbps per OCP rack unit | A 1RU switch can expose about 4X the front-panel bandwidth of a 1600G-OSFP design. |
| Integrated cold plate (up to 400W) | Liquid cooling is built into the module instead of treated as an external workaround. |
| Linear, half-retimed, or fully-retimed interfaces | Flexible interface options let designers trade power against signal-integrity margin. |
| DR, FR, LR, SR, ZR/ZR+ and beyond | Covers in-rack to metro reach, including coherent-lite and RF/microwave variants. |
These numbers change the design question. Instead of asking only what speed a module runs, architects now have to ask how much front-panel bandwidth the switch can expose, how many switch racks a target GPU count actually needs, whether the facility can supply the cooling loop, which interface model the platform requires, and what maintenance model the cluster can live with.
XPO vs OSFP vs CPO
XPO is best read as a bridge between today's high-volume pluggables and more integrated future optics, not a winner-takes-all replacement for either.
| Technology | Core idea | Main strength | Main limitation |
|---|---|---|---|
| OSFP | Widely deployed high-speed pluggable form factor | Mature ecosystem, high volume, serviceable, broad standards support | AI-scale density and cooling are pushing past its design envelope |
| XPO | Extra-dense, liquid-cooled pluggable optics | Much higher density while keeping field serviceability | Needs new switch designs and a liquid-cooling-ready facility |
| CPO | Optics integrated next to or with the switch ASIC | Shortest electrical paths, potential power and signal gains | Harder manufacturing, testing, serviceability, and upgrades |
| LPO / linear optics | Pluggable optics that lean on the host DSP | Lower power and latency potential | Demands strong host signal integrity; does not solve density |
XPO vs OSFP: Density and Cooling
The honest framing is that XPO is not a drop-in OSFP upgrade. They share the pluggable model, but XPO needs a different switch cage and a cooling loop. For most current 400G and 800G deployments, OSFP is still the safer near-term choice. XPO becomes the better option only when faceplate density and cooling capacity are both genuine limits, which is mainly the case at the top end of AI build-outs.
XPO vs CPO: Serviceability vs Integration
CPO is not a failure, and XPO is not a full substitute for it. They solve different problems at different layers. CPO chases the lowest possible power and latency by integrating at the package, accepting harder serviceability and manufacturing as the trade. XPO keeps modules replaceable and standards-flexible, which suits operators whose workflows already revolve around pluggable inventory and incremental upgrades. Where you land depends on whether package-level power savings or field serviceability matters more for your fabric.
A Practical Comparison: A 204.8T Switch With XPO vs OSFP
The density claim is easier to judge with a concrete build. As Marvell, an XPO founding member, describes, a 204.8T switch needs just 16 XPO modules inside a single 1U chassis, versus 128 1.6T pluggable modules across a 4U chassis to reach the same capacity. Extended across a full scale-up and scale-out build, Marvell estimates XPO can cut the rack space for optical modules by up to 75% and overall floor space by roughly 44%.
That footprint reduction is where the cabling story gets interesting. Fewer modules and racks mean fewer fiber connections, less congestion, and cleaner airflow paths, but high density does not make cabling discipline optional. With this many parallel lanes terminating in one place, connector and polarity choices decide whether the rack stays serviceable, so it is worth being deliberate about choosing between MTP and MPO before you commit to a high-density layout. The point is not that XPO eliminates cabling work; it concentrates it, which raises the cost of getting it wrong.
Where XPO Fits in AI Network Architectures
Scale-Up Fabrics
Scale-up networks bind accelerators tightly inside a high-performance domain, and these links are the most sensitive to latency, bandwidth, and reliability. XPO fits here when the design needs extreme density near GPU clusters and the rack is already liquid-cooled. For the shortest in-room hops, SR-type optics over multimode fiber still apply, and the practical reach there is easy to overestimate, so check the multimode fiber distance limits against your actual runs before standardizing on a media type.
Scale-Out Fabrics
Scale-out networks stitch many servers, racks, and GPU pods into one training fabric. As clusters grow from thousands to tens of thousands of accelerators, the sheer number of optical links becomes the management problem, and denser modules directly reduce switch count, cabling pressure, and floor space. This is the layer where XPO's density math pays off most clearly.
Scale-Across and Metro Reach
Arista positions XPO for scale-across and metro fabrics too, not just in-hall links, because AI infrastructure is increasingly spread across halls, buildings, and campuses. In those designs the same module family has to serve both short reaches and coherent long reaches, which is why XPO's support for DR, FR, LR, and ZR/ZR+ in one form factor is part of the pitch.
XPO Is Not for Every Data Center
Treating XPO as universally better is the wrong read. If you run a standard enterprise data center, a moderate cloud, or an air-cooled facility, retrofitting a liquid loop just to gain optical density rarely pencils out, and OSFP plus current 400G/800G/1.6T pluggables will serve you better for the near term. The same goes for teams deploying this year with low risk tolerance: a form factor whose production hardware and ecosystem are still maturing is not where you want a critical path. XPO earns its place at the top end of AI build-outs, not on every link.
FAQ: XPO Transceivers
Q: What does XPO stand for?
A: XPO stands for eXtra-dense Pluggable Optics, a liquid-cooled, high-density pluggable optical module form factor defined by an Arista-led multi-source agreement for AI data center networks.
Q: Is XPO the same as CPO?
A: No. CPO (co-packaged optics) integrates the optics next to the switch ASIC and changes how the system is repaired and upgraded. XPO stays pluggable and field-replaceable from the front panel, prioritizing serviceability while still raising density and adding liquid cooling.
Q: Can XPO replace OSFP?
A: Not broadly, and not soon. OSFP remains the dominant form factor and will keep serving most 800G and 1.6T links. XPO targets the highest-density AI fabrics, and it requires new switches and a cooling loop, so it complements OSFP rather than replacing it everywhere.
Q: Is XPO available for production deployment yet?
A: Not yet. The XPO MSA launched in March 2026 with live prototypes at OFC 2026, and industry analysts expect production hardware around 2027. For now it is a planning and evaluation target, not a shipping product.
Q: Why does XPO need liquid cooling?
A: At 12.8 Tbps with 64 lanes per module, the heat load is well beyond what airflow handles efficiently. XPO's integrated cold plate, rated to 400W per module, lets it run in the liquid-cooled racks that large AI data centers are already adopting.
Q: What is the difference between XPO and LPO?
A: LPO (linear pluggable optics) lowers power by leaning on the host DSP, but it does not raise module density. XPO raises both bandwidth density and thermal capacity, and it can itself use a low-power linear interface, so the two ideas address different constraints.
The Bottom Line
XPO marks a real shift in AI data center optics: extreme front-panel density and built-in liquid cooling, without giving up the pluggable, field-replaceable model operators rely on. It is not a universal OSFP replacement, and it is not yet shipping, so the right move for most teams is to understand it, map it against the decision framework above, and watch ecosystem maturity rather than rush a deployment. Whatever form factor you standardize on, the fiber plant behind it still has to be planned with care, and our fiber optic cabling solutions can help you build a structured foundation that carries 800G and 1.6T today and is ready for what comes next.
