Sec-CH-UA-Full-Version-List

Sec-CH-UA-Full-Version-List is Sec-CH-UA with the resolution turned up: the same brand list, but each brand carries its complete version number instead of just the major.

Accept-CH: Sec-CH-UA-Full-Version-List

Sec-CH-UA-Full-Version-List: "Chromium";v="126.0.6478.127",
  "Google Chrome";v="126.0.6478.127", "Not/A)Brand";v="8.0.0.0"

Full build numbers are one of the strongest fingerprinting signals a browser can emit (they can identify an individual rollout cohort), which is why this data moved out of the default User-Agent string (see User-Agent reduction) and now requires an explicit Accept-CH opt-in.

Legitimate reasons to request it

• Security telemetry: correlating traffic with known-vulnerable browser builds, or gating access from versions with known exploits.
• Bug triage: a crash reproducible only in 126.0.6478.127 needs the full number; the major version is useless.
• Bot and fraud analysis: mismatches between the claimed full version and observed behavior (TLS fingerprint, JS features) are a classic spoofing tell.

If all you need is “Chrome 126 or newer”, stay with the default Sec-CH-UA and leave this one alone; every hint you request is entropy you become responsible for.

The same GREASE rules apply

The fake brand entry is still there, still with junk punctuation, and brand order is still randomized. Parse it as a structured-field list and look up brands by name.

In JavaScript

const { fullVersionList } = await navigator.userAgentData
  .getHighEntropyValues(['fullVersionList']);
// [{ brand: "Chromium", version: "126.0.6478.127" }, ...]

This hint supersedes the deprecated single-value Sec-CH-UA-Full-Version.