Cat8 was standardized in 2016 to carry 25/40 Gb/s over copper at short distances — specifically for data center top-of-rack to end-of-row runs. Ten years later it has found a small, defensible niche and no more than that. Fiber has continued to win everything longer than a rack unit hop, and the gap keeps growing.
- Cat8 reach is 30 m maximum; above that, fiber is required.
- Cat8 uses larger, stiffer cable with 2 GHz bandwidth.
- Fiber uplinks (100/400G) are cheaper per-Gb than Cat8 40G in most deployments.
- Cat8 has a niche; it is not a general data center answer.
Executive summary
Cat8 is a valid choice for short intra-cabinet or top-of-rack to nearby cabinet copper runs where 25/40 Gb/s over copper is preferred and reach is under 30 m. For anything longer or higher speed, fiber is the correct answer.
Where the debate is real
Some data center operators prefer copper for short high-speed links because BASE-T optics are absent from switch product lines. Cat8 fills that gap where fiber optics would otherwise be needed. Outside of that specific case, fiber wins on cost, weight, and future-proofing.
Side-by-side
| Attribute | Cat8 | OM4 fiber |
|---|---|---|
| Max speed | 40 Gb/s | 400 Gb/s+ with modern optics |
| Max distance at top speed | 30 m | 150 m at 400G |
| Bandwidth | 2 GHz | n/a (optical) |
| Cable OD | ~0.35 in | ~0.20 in |
| Termination | Cat8-rated jacks | LC or MTP |
| Typical use | Short intra-rack copper | All backbone and long runs |
Common mistakes
- Speccing Cat8 for horizontal runs to workstations — reach is inadequate.
- Assuming BASE-T optics are always available — many switches only offer SFP+.
- Mixing Cat8 and Cat6A in the same pathway without accounting for the OD difference.
Best practices
- Fiber for anything beyond a single rack row.
- Cat8 only where the switch fleet lacks appropriate optics and reach is short.
- Validate optics availability at spec time; retrofitting to fiber is expensive.
When to call a professional
Any data center design that considers Cat8 should be reviewed with a fiber-experienced designer before commitment. The optics ecosystem changes annually; what was Cat8's advantage this year may not be next year.