Why do I get "eval" in the CLI prompt?

When I SSH in to my BIG-IP appliance the prompt says:

[root@bigip01:Eval:Active:Standalone]

Why does it say Eval? It's licensed with "best" and has SWG added.

[root@bigip01:Eval:Active:Standalone] log  tmsh show sys license

Sys::License
Licensed Version         12.1.1
Registration key         *****
Licensed On              2017/05/29
Service Check Date       2017/08/22
Platform ID              C115
Appliance Serial Number  ********

Active Modules
  Access Policy Manager, Base, i46XX (****)
    Anti-Virus Checks
    Base Endpoint Security Checks
    Firewall Checks
    Network Access
    Secure Virtual Keyboard
    APM, Web Application
    Machine Certificate Checks
    Protected Workspace
    Remote Desktop
    App Tunnel
  Best Bundle, i4600 (******)
    Rate Shaping
    DNSSEC
    DNS Services
    SDN Services
    BIG-IP, DNS (Max)
    Routing Bundle
    Advanced Firewall Manager, i4XXX
    Application Security Manager, i4XXX
    GTM Licensed Objects, Unlimited
    DNS Rate Fallback, Unlimited
    DNS Licensed Objects, Unlimited
    GTM Rate Fallback, (UNLIMITED)
    DNS Rate Limit, Unlimited QPS
    GTM Rate, Unlimited
    CGN, BIG-IP, AFM ONLY
    Max Compression, i4600
    Max SSL, i4600
    Protocol Security Manager

Time Limited Modules
  Secure Web Gateway, 1Yr, 4XXX/i4XXX|*********|20170822|20180823|SUBSCRIPTION