The official name of XPO is eXtra sense Pluggable Optics, an ultra high density pluggable optical module. Led by Arista, MSA was established and publicly launched by 45 optical communication companies on March 12, 2026. The core solution is a single module with 12.8 Tbps, cold plate liquid cooling, and a front panel density four times that of 1.6T OSFP.

The current bottleneck of OSFP

OSFP (Octal Small Form Factor Pluggable) is a plug-in optical module specification proposed in 2016, and it is also the main front panel of the 800G and 1.6T era. The Arista white paper states that a maximum of 32 OSFP modules can be plugged into a 1 RU front panel. A 51.2T switch can support up to 1U with 32 1.6T OSFPs, which is already the upper limit of OSFP form in terms of panel density. The problem arises in the next generation: the switching capacity doubles to 102.4T (corresponding to new generation chips such as Broadcom Tomahawk 6 and NVIDIA Spectrum-X). If you continue to use OSFP, you will encounter the following problems.

Insufficient panel space: 102.4T requires 64 1.6T OSFP modules → 2 RU; 204.8T requires 4 RU. The pressure of cabinet density is doubled.
Electrical channel collision with wall: The wiring from ASIC to front panel PCB is on the order of tens of centimeters. At 200G PAM4 (224G electrical speed), the accumulated line insertion loss, crosstalk, and jitter are approaching their limits. Continuing to stack modules requires stacking retimers, causing power consumption to take off.
Power supply and heat dissipation hitting the wall: According to the common DSP/coherent module caliber, the operating power consumption of a single module 800G OSFP is about ten to twenty watts. No matter how many modules are air-cooled, they won't be able to dissipate the heat.
This is not a "more expensive" engineering problem, but a simultaneous failure of physical constraints. There are two major directions to solve this problem in the field of optical modules, namely: changing the architecture, moving the optical engine to the ASIC chip side, and reducing the wiring from tens of centimeters to millimeter level. This is the idea of CPO and NPO, which is to change the underlying packaging of switches; The idea of XPO is to expand the module itself by adding 8 OSFP bandwidths into one module and using liquid cooling for heat dissipation. The modification is on the front panel.
XPO is the answer to 'not changing architecture, changing modules'.

What exactly has XPO changed

Simply put, XPO is a new type of pluggable optical module with a single module bandwidth of 12.8 Tbps. It relies on cold plate liquid cooling to dissipate heat, increasing the front panel density to four times that of 1.6T OSFP.

There are mainly three changes as follows.

The bandwidth of a single module jumps from 1.6T to 12.8T. An XPO module needs to accommodate 64 electrical channels, each with 200 G/lane PAM4, equivalent to combining all signals from 8 1.6T OSFPs into one module. Sixteen XPO modules aggregate 204.8 Tbps, packed within 1 OU. Compared to the OSFP era where 32 1.6T modules=51.2T/RU density, XPO increases the accessible bandwidth of a unit cabinet by four times.
Air cooled to liquid cooled plate. The top of XPO is an integrated cold plate, with a maximum thermal budget design limit of 400W/module. The cold plate is directly attached to the ASIC heating chip and optical components, and carries away heat through a liquid cooling circuit. That is to say, the temperature of the internal components of the XPO module is 20-25 ° C lower than that of the air-cooled OSFP. When the temperature drops, the reliability improves, and the MTBF margin also increases.
The circuit components inside the module are greatly simplified. According to Arista data, a 32 channel XPO motherboard only requires 1 microcontroller and 1 set of power converters, which corresponds to approximately 4 sets of OSFP combinations with the same bandwidth. After the overall shared logic, the number of internal components in the module decreased by about 75%. This is the direct benefit of merging 8 modules into 1, as many repetitive management circuits only need to be done once.
Together, XPO's commitment is to "save panel space by 4 times, double heat dissipation capacity, and reduce internal components by 75%".

What to keep, what not to keep

Key fact that is easily overlooked by readers: Many aspects of XPO are intentionally preserved.
XPO retains the front panel's pluggable form, allowing maintenance personnel to unscrew screws, remove modules, and insert new modules. Replacement is still counted in minutes, and there is no need to shut down the entire switch for maintenance. Multi vendor interchangeability allows XPO modules from different vendors to be plugged into the same switch as long as they meet MSA specifications. The standard optical interface set covers all existing optical interface categories such as DR/FR/LR/SR/ZR/Zr+, and the existing fiber infrastructure does not need to be rebuilt. Independent optical transceiver logic, each XPO module completes its own electro-optical conversion, ASIC only outputs electrical signals and does not directly touch light.

Changed the heat dissipation method from air cooling to cold plate liquid cooling. The single module bandwidth has increased from 1.6T to 12.8T. The physical size of the module has increased, approximately 2.7 × wider than OSFP. The electrical interface speed has been increased from 100G/lane to 200G/lane PAM4.

What remains unchanged is that the ASIC chip, Broadcom Tomahawk 6 or Jericho 4, is still the original ASIC and does not require a new chip for XPO. The wiring topology of the motherboard PCB, the electrical signal still travels from the ASIC to the front panel module cage, but the destination is changed from the OSFP cage to the XPO cage. The encapsulation method of the optical engine is that the optical engine is still inside the pluggable module and has not been moved to the ASIC substrate.

Putting "what has been changed and what hasn't been changed" together reveals XPO's engineering philosophy, which is radical in the front panel layer and keeps the ASIC layer stable.

Put it into the CPO/NPO coordinate system to see
The quickest way to understand XPO is to look at its respective positions when placed together with OSFP/CPO/NPO.
The fundamental difference between the four is a simple geometric question of how far away the optical engine is from the ASIC chip. It can be roughly understood as: CPO is an optical engine implemented on ASIC substrates, with wiring on the millimeter scale; NPO is an optical engine plugged into a socket next to ASIC, with wiring in the centimeter range; OSFP/XPO is an optical engine located in a front panel pluggable module, with wiring on the order of tens of centimeters.
The shorter the wiring, the smaller the signal attenuation, the less DSP/timer required, and the lower the power consumption; But the shorter the routing, the deeper the system hierarchy that needs to be changed.

维度	OSFP（今天）	XPO（新方案）	NPO	CPO
改动层级	前面板可插拔	前面板可插拔	基板外插座	ASIC 基板内
单模块带宽	800G / 1.6T	12.8T	Lightmatter L20：12.8T aggregate（6.4T each direction）	交换机级（Broadcom Davisson 102.4T）
单位带宽功耗	按常见模块口径十几到二十多瓦	按 400W 冷板上限粗算，ceiling 约 25W/800G（非典型工作点）	目标显著低于传统 pluggable	较 pluggable 降约 65%（Broadcom 官方口径；据 Meta ECOC 论文约 5.4W/800G）
面板密度	51.2T / 1 RU	204.8T / 1 OU	不适用（在基板上）	不适用（在基板上）
散热	风冷	冷板液冷	系统级散热	ASIC 共冷
可维护性	热插拔，现场换	热插拔 + 液冷接头	插座式可换，整机停机	坏了基本换整机
量产状态	已量产	据报道 2027	Demo 阶段（阿里云 102.4T 已展示）	Broadcom TH6-Davisson 2025-10 发布；NVIDIA Quantum-X 官方口径 2025 年内可用、Spectrum-X Photonics 2026 年推出
供应链冲击	基线	小（延伸现有模块生态）	中（光引擎是新环节）	大（改 ASIC 封装）

A few numbers in the table are worth noting specifically:

XPO unit bandwidth power consumption: The official XPO specification is "cold plate hot budget up to 400W/module". 400W is the upper limit for covering the highest scenarios such as coherent lite and ZR, and the typical operating power consumption will be lower than this number. Roughly estimating the ceiling by dividing 400W into 16 800G channels, it is approximately 25W/800G. But this is a rough calculation of the upper limit of thermal design, not a typical working value measured, and should not be compared accurately with the measured or paper values of CPO/NPO.

CPO power saving range: Broadcom disclosed in ECOC 2025 that TH5 Bailly CPO reduces power consumption by about 65% compared to traditional plug-in; The collaborative paper between Meta and Broadcom provides a specific number of approximately 5.4W/800G.

XPO panel density of 204.8T/1OU: This is the hardest selling point of XPO. One OCP rack unit can accommodate 16 XPO modules, each with 12.8T, resulting in an aggregate of 204.8T. This corresponds to the physical installation requirements of the next generation 102.4T/204.8T switches, which is four times higher than the 51.2T/RU in the OSFP era.

After seeing this table clearly, many confusions become apparent:

● XPO is not a substitute for CPO, and the changes made by the two are not at the same level (front panel vs ASIC substrate)
● XPO is not a "more energy-efficient module" either. Its advantages are density and heat dissipation, not energy consumption per bit
● The core value of XPO is to "exchange the density of the front panel with liquid cooling", rather than "exchange for a better light engine"