On QFX5120-48Y, there is no information of auto negotiation for SFP-T in show interface extensive output. This is a software bug which has been fixed in certain software releases. This KB describes the details on this issue.

According to the technical document, QFX5120-48Y is supporting auto negotiation for SFP-T.
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Channelizing Interfaces on QFX5120-48Y Switches
QFX5120-48Y does not support autonegotiation when 1-gigabit fiber SFP transceiver is plugged in. In such cases, it is recommended to disable auto-negotiation on the remote end device. But, QFX5120-48Y switches with 1-gigabit copper SFP transceiver supports autonegotiation, as the physical layer within the transceiver handles autonegotiation.
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However, its information is not displayed as expected.
Here is the sample output, no information of auto negotiation on QFX5120-48Y.

root@QFX5120-48Y> show chassis hardware | match SFP-T
    Xcvr 31      REV 01   740-038291   XXXXXXX           SFP-T

root@QFX5120-48Y> show interfaces ge-0/0/31 extensive | match nego

{master:0}
root@QFX5120-48Y>

Here is the expected information of auto negotiation.

root@QFX5120-48Y> show chassis hardware | match SFP-T
    Xcvr 31      REV 01   740-038291   XXXXXXX           SFP-T

root@QFX5120-48Y> show interfaces ge-0/0/31 extensive | match nego
  Auto-negotiation: Enabled, Remote fault: Online, Media type: Copper, IEEE 802.3az Energy Efficient Ethernet: Disabled, Auto-MDIX: Enabled
  Autonegotiation information:
    Negotiation status: Incomplete

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This is a software bug which has been fixed through PR1739808.
https://prsearch.juniper.net/problemreport/PR1739808
This is a display bug which does not affect function of auto negotiation.

2023-07-31 : Created a KB