Sure, history time (feeling old now). In the very old days (Anyconnect 2.x and 3.x) we had a different licensing model: Anyconnect Essentials, Anyconnect Premium and add-ons like Anyconnect for mobile, Anyconnect for Phones, Advanced Endpoint Assesment.
Anyconnect Essentials allowed just basic VPN connection via SSL or IKEv2, this was intended for customers coming from the legacy IPSec VPN Client that did not need advanced features of anyconnect or clientless.
Then starting with Anyconnect 4.x we simplified the licensing model and started offering Anyconnect Plus and Anyconnect Apex (now rebranded to Anyconnect Advantage and Anyconnect Premier) https://www.cisco.com/c/en/us/products/collateral/security/anyconnect-secure-mobility-client/secure-client-og.html#3Licenses
In this picture you can see the features mapping from the old licensing model to the new one:
Essentials and Premium are discontinued licenses and should not co-exist with Advantage (formerly Plus) or Apex (formerly Apex). The old licensing model applied only to Anyconnect 3.x which is EoL:
https://www.cisco.com/c/en/us/products/collateral/security/anyconnect-secure-mobility-client/eos-eol-notice-c51-734084.html
https://www.cisco.com/c/en/us/support/docs/security/anyconnect-secure-mobility-client/200191-AnyConnect-Licensing-Frequently-Asked-Qu.html#anc28
https://www.cisco.com/c/en/us/support/docs/security/anyconnect-secure-mobility-client/200191-AnyConnect-Licensing-Frequently-Asked-Qu.html#anc42
- You need to make sure you have the right licensing to be compliant.
- Essentials should not even be configured as it's discontinued.
- Disabling essentials with the "no anyconnect-essentials" will not have any impact in terms of number of users as you have the same amount of Premium Licenses (10K) from the "sh version".
- After 4.9 since we removed unsecure algorithms, Anyconnect clients will not be able to establish IKEv2 sessions to headends with anyconnect-essentials enabled or Advantage (formerly Plus). It will require Premier (formerly Apex): https://www.cisco.com/c/en/us/products/collateral/security/anyconnect-secure-mobility-client/secure-client-og.html#3Licenses
