diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 6ad8522..5f7988f 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -9,7 +9,10 @@ env:
   CARGO_TERM_COLOR: always
   # Pin the toolchain to the declared MSRV so CI matches production.
   RUST_TOOLCHAIN: 1.90.0
-  GO_VERSION: "1.25.0"
+  # The differential check compares Rust against net/http behaviour, which
+  # changes between Go releases (e.g. ServeMux redirects 301 -> 307), so the
+  # reference must be built with the same Go the Rust port mirrors.
+  GO_VERSION: "1.27.3"
 
 jobs:
   rust:
diff --git a/README.md b/README.md
index b76f77e..7df5762 100644
--- a/README.md
+++ b/README.md
@@ -124,7 +124,8 @@ against the same `BALANCE_DB_PATH`; do not run both writers simultaneously.
 Existing accounts, access/refresh tokens and saved device cursors remain usable.
 See [deployment and rollback](docs/DEPLOYMENT.md) for the full procedure.
 
-Verify the implementations locally with Go 1.25+, Rust and Python 3:
+Verify the implementations locally with Go 1.27.3 (the version CI uses for the
+differential check), Rust and Python 3:
 
 ```sh
 cargo test --locked
diff --git a/docs/DEVELOPMENT.md b/docs/DEVELOPMENT.md
index fd38cf6..1c2923f 100644
--- a/docs/DEVELOPMENT.md
+++ b/docs/DEVELOPMENT.md
@@ -2,7 +2,7 @@
 
 ## Требования
 
-Production-сервер использует Rust 1.90+ и bundled SQLite. Go 1.25+ нужен для сохранённой эталонной реализации и differential-проверок. Python 3 используется без сторонних пакетов.
+Production-сервер использует Rust 1.90+ и bundled SQLite. Go 1.25+ нужен для сохранённой эталонной реализации; differential-проверки (`tools/compatibility.py`) требуют Go 1.27.3, как в CI: поведение `net/http` (например, код редиректа ServeMux 301/307) зависит от версии Go. Python 3 используется без сторонних пакетов.
 
 Проверить локальную версию: