How ISP proxies work
A proxy provider partners with a consumer ISP (or gets a sub-allocation of addresses from one) so it can run a block of IPs registered under that ISP's ASN. The IPs physically live in the provider's datacenter, but the public records that say who owns them — BGP announcements (how networks tell the internet which IPs they route) and WHOIS (the public registry of IP ownership) — list the consumer ISP. So when an anti-bot system looks up the ASN, the IP appears to be an ordinary Comcast or BT home connection, not a datacenter IP.
Because the IP never changes and the provider owns the hardware, there is no rotation by default. You lease one specific IP for a fixed term (monthly or yearly), and for that period it is yours alone or shared by a small group.
Why multi-request scoring rewards ISP static
Multi-request bot managers score you across many requests, not just one: trust builds up as the same client keeps making consistent, successful requests. Its _abck cookie starts as untrusted (~-1~) and flips to trusted (~0~) after the first successful sensor.js POST — the data the sensor script collects about your browser — then stays trusted as long as the session looks consistent. If you swap to a different residential IP partway through, that built-up trust resets, because the system now sees a brand-new, unproven client. A static ISP IP keeps the same identity for hours or days, which is exactly how a real person browses from home.
For scraping that depends on being logged in (account workflows, a persistent shopping cart), ISP static is the only sensible choice, since the session cookies have to stay attached to one stable identity.
When to use ISP vs residential vs mobile
ISP static: long sessions, multi-request trust scoring, account-tied scraping — anything where trust needs to build up across multiple requests.
Rotating residential: lots of independent requests where each one stands alone as its own session — search scraping, SERP collection (search-results pages), listing snapshots.
Mobile: the toughest anti-bot targets, where the IP's reputation by itself decides whether you get through.
On cost: ISP at roughly $2 per IP per month, supporting hundreds of long-lived sessions, is far cheaper than the per-gigabyte pricing of rotating residential for the same job.