400G QSFP-DD vs OSFP: How to Choose the Right Module (SR8, DR4, FR4, LR4) in 2025?

The shift to 400G networking is no longer optional for hyperscale data centers, AI/ML clusters, and 5G backbones. But procurement teams face a dilemma: QSFP-DD or OSFP? SR8, DR4, LR4, or 400G-QDD-FR4 Transceivers? Costs are high, compatibility worries are real, and lead times are shrinking. This guide cuts through the noise.

Snippet (Featured Answer):
400G QSFP-DD and OSFP both deliver 400Gbps using 8×50G PAM4 lanes. QSFP-DD is backward compatible with QSFP28, ideal for gradual upgrades. OSFP is slightly larger, with better thermal management, supporting higher power optics for AI and HPC clusters. SR8 is best for ≤100m multimode, DR4 for 500m SMF, FR4 for 2km, and LR4 for 10km links. ¹

I saw this debate firsthand at a client’s AI training cluster deployment. The vendor recommended OSFP for cooling efficiency, but the network team needed QSFP-DD for reuse of existing QSFP28 panels. The compromise? A dual-path strategy: QSFP-DD for core aggregation and OSFP for GPU-to-GPU interconnects. The result—smooth migration without forklift upgrades.

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What are the differences between 400G QSFP-DD and OSFP form factors?

Both QSFP-DD and OSFP were created to handle 400G and beyond, but their design philosophies differ.

Snippet:
QSFP-DD extends QSFP to double density (8 lanes) while keeping the same compact size, ensuring backward compatibility with QSFP28. OSFP is a new, larger module with improved cooling and higher power support, but no backward compatibility. ²

QSFP-DD (Quad Small Form Factor Pluggable – Double Density)

• Derived from QSFP form factor, doubles electrical lanes to 8×50G PAM4.
• Backward compatible with QSFP28 ports.
• Compact design for smooth upgrades in data centers.
• Power dissipation up to ~14–16W.
• Common for 400G SR8, DR4, FR4, LR4 optics.

OSFP (Octal Small Form Factor Pluggable)

• Brand-new form factor, slightly wider and deeper than QSFP-DD.
• No backward compatibility with QSFP28.
• Better thermal management, handles 15–20W+ optics.
• Supports future 800G optics (8×100G PAM4).
• Strong fit for HPC, AI/ML fabrics, and 5G networks.

Feature	QSFP-DD	OSFP
Size	Compact, same as QSFP28	Larger, wider, deeper
Backward comp.	✅ Yes (QSFP/QSFP28)	❌ No
Power support	~14–16W	Up to 20W+
Cooling	Moderate	Excellent, more surface area
Upgrade path	Smooth to 400G from 100G	Future-proof for 800G
Ecosystem	Strong, widespread	Growing fast in AI/HPC clusters

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SR8 vs DR4 vs FR4 vs LR4: Which 400G optics fit your distance and fiber plant?

400G modules come in several optical variants. Picking the right one depends on reach, fiber type, and connector availability.

Snippet:
SR8: ≤100m OM3/OM4 MMF with MPO-16. DR4: 500m SMF with MPO-12. FR4: 2km SMF with duplex LC. LR4: 10km SMF with duplex LC. Match reach and fiber plant before ordering. ³

Quick comparison of 400G optical types

Module	Reach	Fiber Type	Connector	Typical Use
400G SR8	70m (OM3), 100m (OM4)	MMF	MPO-16	Short-reach in racks, leaf-spine
400G DR4	500m	SMF	MPO-12	Campus, TOR–spine links
400G FR4	2 km	SMF	LC duplex	Metro/DCI short-haul
400G LR4	10 km	SMF	LC duplex	Metro aggregation, DCI

Pro tip: FR4 often wins on total cost for 1–2 km links since it uses just 2 fibers, while DR4 consumes 8. But if your backbone is already MPO-12 based, DR4 simplifies rollout. ⁴

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Where are 400G modules used in real-world projects?

The jump to 400G is driven by workloads, not marketing. Here’s where they land:

Snippet:
400G transceivers are widely used in AI/ML clusters, hyperscale cloud, high-performance computing, 5G transport, and metro/DCI interconnects. OSFP is favored in AI fabrics for cooling, while QSFP-DD fits upgrades from 100G QSFP28. ⁵

Typical applications

• AI/ML clusters: OSFP SR8 or DR4 between GPU servers.
• Hyperscale data centers: QSFP-DD FR4 for spine-to-spine.
• HPC fabrics: OSFP LR4 where long SMF reach is required.
• 5G metro transport: QSFP-DD LR4 for 10 km links.
• DCI (Data Center Interconnect): FR4 or LR4 depending on site distance.

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Compatibility & coding: avoiding vendor lock-in

400G modules are expensive. Avoid paying OEM premiums without testing.

Snippet:
Request CMIS compliance, coding screenshots, and DOM accuracy proof from vendors. Run a quick acceptance checklist (loopback, BER, DOM). This prevents lock-in and ensures multi-vendor operation. ⁶

Quick acceptance checklist

1. Insert into target NOS (Cisco, Arista, Juniper).
2. Run show interface transceiver—check coding.
3. Verify DOM/DDM data (Tx/Rx, temp, Vcc).
4. Loopback test for BER errors.
5. Confirm reach against fiber plant.

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ABPTEL advantage in 400G procurement

Choosing between OEM and third-party can make or break budgets. Here’s why ABPTEL stands out:

• Price advantage: competitive vs OEM with global delivery.
• After-sales support: fast DOA replacement and RMA SLA.
• OEM/ODM options: custom EEPROM coding, labeling, packaging.
• 400G product line: QSFP-DD and OSFP, covering SR8, DR4, FR4, LR4.
• Logistics: stable stock on SR8/DR4, predictable lead time on FR4/LR4.

Explore: 400G QSFP-DD/OSFP Transceivers

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A simple decision tree for 400G rollout

Step 1: What’s your distance?

• ≤100m → SR8 (MPO-16)
• 500m → DR4 (MPO-12)
• 2 km → FR4 (LC duplex)
• 10 km → LR4 (LC duplex)

Step 2: What’s your fiber plant?

• OM3/OM4 MMF → SR8
• SMF backbone (MPO-12) → DR4
• SMF duplex LC → FR4/LR4

Step 3: Platform choice

• Need backward compatibility → QSFP-DD
• Need future 800G scalability → OSFP

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Call to action

Ready to evaluate 400G?

• Browse: 400G QSFP-DD/OSFP Transceivers
• Explore: AOC & DAC Cables for ≤30m links.
• Learn: MTP/MPO Cables for backbone builds.

📧 Email Candy (Shenzhen, China) at Candy@abptel.com for samples, quotes, and OEM/ODM requests.

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