AnyConnect supports many cipher suites. The one that is chosen is the strongest mutually agreeable as configured on the VPN headend (ASA or FTD or IOS router) to which it connects.
The AnyConnect client itself has only some non-comprehensive references to what's supported in the product data sheet:
https://www.cisco.com/c/en/us/products/collateral/security/anyconnect-secure-mobility-client/datasheet-c78-733184.html?cachemode=refresh
Is there a specific requirement you are looking to know about? We generally negotiate a pretty strong connection assuming the headend is capable of it. Here's me connecting to my lab running FTD 6.6:
> show vpn-sessiondb detail anyconnect
Session Type: AnyConnect Detailed
Username : adm-marvin Index : 5
Assigned IP : 172.31.1.211 Public IP : 192.168.0.165
Protocol : AnyConnect-Parent SSL-Tunnel DTLS-Tunnel
License : AnyConnect Premium
Encryption : AnyConnect-Parent: (1)none SSL-Tunnel: (1)AES-GCM-256 DTLS-Tunnel: (1)AES-GCM-256
Hashing : AnyConnect-Parent: (1)none SSL-Tunnel: (1)SHA384 DTLS-Tunnel: (1)SHA384
Bytes Tx : 55647 Bytes Rx : 51746
Pkts Tx : 138 Pkts Rx : 400
Pkts Tx Drop : 0 Pkts Rx Drop : 0
Group Policy : CCIELab_GP Tunnel Group : CCIELab-VPN
Login Time : 13:04:31 UTC Sun May 10 2020
Duration : 0h:01m:51s
Inactivity : 0h:00m:00s
VLAN Mapping : N/A VLAN : none
Audt Sess ID : ac1f0101000050005eb7fbdf
Security Grp : none Tunnel Zone : 0
AnyConnect-Parent Tunnels: 1
SSL-Tunnel Tunnels: 1
DTLS-Tunnel Tunnels: 1
AnyConnect-Parent:
Tunnel ID : 5.1
Public IP : 192.168.0.165
Encryption : none Hashing : none
TCP Src Port : 5859 TCP Dst Port : 443
Auth Mode : userPassword
Idle Time Out: 30 Minutes Idle TO Left : 28 Minutes
Client OS : win
Client OS Ver: 10.0.18363
Client Type : AnyConnect
Client Ver : Cisco AnyConnect VPN Agent for Windows 4.8.03052
Bytes Tx : 8136 Bytes Rx : 0
Pkts Tx : 6 Pkts Rx : 0
Pkts Tx Drop : 0 Pkts Rx Drop : 0
SSL-Tunnel:
Tunnel ID : 5.2
Assigned IP : 172.31.1.211 Public IP : 192.168.0.165
Encryption : AES-GCM-256 Hashing : SHA384
Ciphersuite : ECDHE-RSA-AES256-GCM-SHA384
Encapsulation: TLSv1.2 TCP Src Port : 5863
TCP Dst Port : 443 Auth Mode : userPassword
Idle Time Out: 30 Minutes Idle TO Left : 28 Minutes
Client OS : Windows
Client Type : SSL VPN Client
Client Ver : Cisco AnyConnect VPN Agent for Windows 4.8.03052
Bytes Tx : 8136 Bytes Rx : 701
Pkts Tx : 6 Pkts Rx : 9
Pkts Tx Drop : 0 Pkts Rx Drop : 0
Filter Name : #ACSACL#-IP-PERMIT_ALL_IPV4_TRAFFIC-57f6b0d3
DTLS-Tunnel:
Tunnel ID : 5.3
Assigned IP : 172.31.1.211 Public IP : 192.168.0.165
Encryption : AES-GCM-256 Hashing : SHA384
Ciphersuite : ECDHE-ECDSA-AES256-GCM-SHA384
Encapsulation: DTLSv1.2 UDP Src Port : 60773
UDP Dst Port : 443 Auth Mode : userPassword
Idle Time Out: 30 Minutes Idle TO Left : 29 Minutes
Client OS : Windows
Client Type : DTLS VPN Client
Client Ver : Cisco AnyConnect VPN Agent for Windows 4.8.03052
Bytes Tx : 39375 Bytes Rx : 51045
Pkts Tx : 126 Pkts Rx : 391
Pkts Tx Drop : 0 Pkts Rx Drop : 0
Filter Name : #ACSACL#-IP-PERMIT_ALL_IPV4_TRAFFIC-57f6b0d3
>
