[Bug] Thunderbolt 5 Devices reporting as running at 40Gbps

[cannotcollide]

What's wrong

Hello again! I've undergone a bit of an upgrade and now have a Thunderbolt 5-equipped MacBook alongside a CalDigit TS5 Dock! Experiencing a bit of a weird issue, though, where despite registering and running at 80Gbps, WhatCable reports said connection as 40Gbps in certain locations, and 80Gbps in others.

I suspect this has something to do with there being 40Gbps in the same daisy-chain, which WhatCable seems to recognise here:

Regardless, it should be denoting the whole connection as 80Gbps. I have an 80Gbps version of the OWC 1M2 coming tomorrow, so I'll let you know if that changes how it reports.

Mac model

M5 Pro MacBook Pro (14-inch, 2025)

macOS version

27.0 latest Public Beta

WhatCable version

v1.5.0 beta 8

Cable

CalDigit Thunderbolt 5 Pro Cable, 2m, 240W, Active

What's plugged into the other end?

CalDigit TS5 Thunderbolt 5 Dock

whatcable --json --raw output

Last login: Tue Sep  8 23:22:47 on console
/Applications/WhatCable.app/Contents/Helpers/whatcable ; exit;                  
redacted@redacted-MBP-183 ~ % /Applications/WhatCable.app/Contents/Helpers/whatcable ; exit;
=== Port-MagSafe 3@1 (MagSafe 3) ===
Nothing connected
Plug a cable into Port-MagSafe 3@1 to see what it can do.

=== Port-USB-C@1 (USB-C) ===
Thunderbolt / USB4 · 98W charger
Supports high-speed data, smart cable.

  What the cable's e-marker reports
    • Cable speed: USB4 Gen 4 (80 Gbps, Thunderbolt 5 class)
    • Cable rated to 50V / 5 A, delivers up to 240W (USB-PD caps at 48V)
    • Active copper cable, re-driver

  What your Mac measured
    • Linked at up to 40 Gb/s × 2
    • Connected via 3 hops: CalDigit, Inc. TS5 → LaCie 1big Dock v2 → Apple Inc. Studio Display
    • Last leg drops from up to 40 Gb/s × 2 to up to 20 Gb/s × 2
    • Connected device: USB Peripheral, CalDigit, Inc. (0x2188) (PD 3.0)
    • Currently negotiated: 20V @ 4.9A (98W)

  What WhatCable knows
    • Made by Lintes Technology Co., Ltd. (0x2B1D), per our bundled vendor list
    • Cable identified as Cable Matters active Thunderbolt 5 cable, 2 m

  What the charger reports
    • Charger advertises up to 98W

Charging: Plugged in, charging on hold
  Charger and cable are fine. macOS has paused charging for now, usually a battery charge limit or Optimized Battery Charging. The Mac still draws power from the charger.

Data: Device runs at 40 Gbps
  This is the fastest the connected device supports. It is not a cable problem.

Display: Display running at full quality
  Your StudioDisplay is connected and the link has the bandwidth for its top mode. Nothing is holding the picture back.
  • Billboard device present

Thunderbolt fabric:
  • CalDigit, Inc. TS5 - Up to 40 Gb/s × 2
    ↳ LaCie 1big Dock v2 - Up to 20 Gb/s × 2
      ↳ Apple Inc. Studio Display - Up to 20 Gb/s × 2

Active tunnels:
  • Video → Apple Inc. Studio Display · adapter 10
  • USB data → CalDigit, Inc. TS5 · adapter 20
  • PCIe data → Apple Inc. Studio Display · adapter 8
  • PCIe data → LaCie 1big Dock v2 · adapter 8
  • PCIe data → CalDigit, Inc. TS5 · adapter 9

Connected devices:
  • CalDigit, Inc. TS5 - Thunderbolt link active at 80 Gbps
    ↳ Display: StudioDisplay · video output 10
    ↳ TS5 USB 2 Hub (CalDigit, Inc.) - High Speed (480 Mbps)
      ↳ TS5 USB 2 Hub (CalDigit, Inc.) - High Speed (480 Mbps)
        ↳ USB Receiver (Logitech) - Full Speed (12 Mbps)
        ↳ 8BitDo Pro 3 Receiver - Full Speed (12 Mbps)
      ↳ TS5 Billboard (CalDigit, Inc.) - Low Speed (1.5 Mbps)
    ↳ TS5 USB 3 Hub (CalDigit, Inc.) - Super Speed+ (10 Gbps)
    ↳ LaCie 1big Dock v2 - Thunderbolt link active at 40 Gbps
      ↳ 1big Dock (LaCie) - High Speed (480 Mbps)
        ↳ 1big Dock HID (LaCie) - Full Speed (12 Mbps)
      ↳ 1big Dock (LaCie) - Super Speed+ (10 Gbps)
        ↳ 1big Dock (LaCie) - Super Speed+ (10 Gbps)
        ↳ 1big Dock CF-SD (LaCie) - Super Speed (5 Gbps)
      ↳ Apple Inc. Studio Display - Thunderbolt link active at 40 Gbps
        ↳ USB2 Hub (Apple) - High Speed (480 Mbps)
        ↳ USB3 Gen2 Hub (Apple) - Super Speed+ (10 Gbps)
          ↳ Rugged Mini SSD (LaCie) - Super Speed+ (10 Gbps)
    ↳ USB3 HUB (Intel Corporation) - Super Speed+ (10 Gbps)

=== Port-USB-C@2 (USB-C) ===
Nothing connected
Plug a cable into Port-USB-C@2 to see what it can do.

=== Port-USB-C@3 (USB-C) ===
Nothing connected
Plug a cable into Port-USB-C@3 to see what it can do.

Saving session...
...copying shared history...
...saving history...truncating history files...
...completed.
Deleting expired sessions...none found.

[Process completed]

System Information cross-check (optional)

TS5:

Vendor Name: CalDigit, Inc.
Device Name: TS5
Mode: USB4 v2
Device ID: 0x51
Vendor ID: 0x2188
Device Revision: 0x2
UID: 0x8087ECE4723E8B00
Route String: 1
Firmware Version: 64.1
Port (Upstream):
Status: Device connected
Link Status: 0x2
Speed: 80 Gb/s
Micro Firmware Version: 1.11.0
Port:
Status: No device connected
Link Status: 0x7
Speed: Up to 120 Gb/s
Micro Firmware Version: 1.11.0
Port:
Status: Device connected
Link Status: 0x2
Speed: 40 Gb/s
Micro Firmware Version: 1.11.0
Port:
Status: No device connected
Link Status: 0x7
Speed: Up to 120 Gb/s
Micro Firmware Version: 1.11.0

1big Dock v2:

Vendor Name: LaCie
Device Name: 1big Dock v2
Mode: Thunderbolt 3
Device ID: 0x1D
Vendor ID: 0x0003
Device Revision: 0x1
UID: 0x0003B1012CE83100
Route String: 501
Firmware Version: 56.1
Port (Upstream):
Status: Device connected
Link Status: 0x2
Speed: 40 Gb/s
Link Controller Firmware Version: 1.41.0
Port:
Status: Device connected
Link Status: 0x2
Speed: 40 Gb/s
Link Controller Firmware Version: 1.41.0

Studio Display:

Vendor Name: Apple Inc.
Device Name: Studio Display
Mode: Thunderbolt 3
Device ID: 0x801F
Vendor ID: 0x0001
Device Revision: 0x1
UID: 0x0001BC6BC9405600
Route String: 30501
Firmware Version: 67.1
Port (Upstream):
Status: Device connected
Link Status: 0x2
Speed: 40 Gb/s
Link Controller Firmware Version: 1.45.0

How often does this happen?

Every time

Anything else

No response

[cannotcollide]

Update: WhatCable is randomly now stating 80Gbps as expected, with no changes on my end.

I'll keep an eye.

[cannotcollide]

now back to 40gbps

[darrylmorley]

@cannotcollide Thanks for this, and all of your reports. Really helpful.

When I started WhatCable I had very little information to work with. Now, with the contributed diagnostics data, and the bug reports, we are in a much better informed position. And, have lots of data that we can test against.

I'm currently taking a larger wholesale look at the codebase. I'm hoping that carefully working through it, from source to view, will fix the majority of the bugs we see today. 🤞

[darrylmorley]

Thanks, the raw output helps a lot. The two figures look like the same link written two ways: 40 Gb/s per lane, two lanes, which is the 80 Gb/s that System Information shows for the TS5. The verdict line is picking up the smaller figure, and that is on our side. It is now part of the Thunderbolt link rework I mentioned.

The flip between 40 and 80 across runs is the part I cannot explain from here. If you have two minutes, Settings > Community > Contribute Diagnostic Data (or whatcable --test-kit in Terminal) sends the raw Thunderbolt tree. Running it while WhatCable is showing 40 would give me the exact state to replay. The OWC 1M2 result is welcome too.

[cannotcollide]

WhatCable is currently showing 40Gbps, so I just ran the community diagnostic.

When the OWC 1M2 80Gbps arrives today, I'll plug it in and run the diagnostic again.

[cannotcollide]

OWC 1M2 arrived, and I don't seem to getting the 40gbps anymore, though I'll keep an eye.

Just ran another community diagnostic, so that should be with you now.