Based on Cisco My Device, my Cisco ASA Firewall 5525-X show that it end of support is 2020-08-31.
Reference link below. Nevertheless, the link shows content related to ASA-CX.
When I check another Cisco web link, no EOL / EOS mentioned on Cisco ASA 5525-X model.
I am confused.
Although 5525-x is not announced EOS yet but it might not going to support future release of firepower/ftd software code.
Instead of buying ASA5525-x, you can go with Firepower 1120/1140/1150. These new appliances offer better performance and come up in a better price also.
Once it is announce EoS , You will still have option to renew the support for some more years if you already have 5525-x.
ASA-CX is completely different software. It was Cisco first try to enter the NGFW market. It never caught up to the competition and eventually Sourcefire was bought.
Cisco has announced EOS/EOL notifications and below is the URL.
EOS for HW: September 4, 2020
Last Date of Support HW : September 30, 2025
I'm confused as well, or at least I was. While everyone talks about EoS and - as was pointed out below - it might not be a wise choice to buy a 5500x in face of the FPR2100 and the new FPR1k devices at this time, Cisco managed to hide the EoL announcement very good. I cannot find it in any of the announcement lists or with any search engine. Product page does also not link to the EoS announcement.. Good Job!
Using the Partner Helpline we managed to get hold of this link https://www.cisco.com/c/en/us/products/collateral/security/asa-firepower-services/eos-eol-notice-c51-743545.html which has the EoS/EoL dates of the 5525, 5545 and 5555 among tons of related licenses.
Afaik, 5508 and 5516 are not EoS for now. Also 5506 (but not the ruggedized and WLAN models) with ASA Image is not yet EoS/L (maybe until FPR1010 also features an image with PoE support? Maybe something still missing for the integrated HW switch?). All the rest of the 5500 family is now EoS (at least announced) in favor of the FPR appliances.