diff --git a/README.md b/README.md
index ae310c0..6c30954 100644
--- a/README.md
+++ b/README.md
@@ -474,6 +474,13 @@ outputs.
     sqrbx-update lazygit      # update, or explicitly install, one tool
     sqrbx-update --list       # list all tools and current versions
 
+Setup and `sqrbx-update` read GitHub release metadata through the GitHub API,
+which allows only 60 unauthenticated requests per hour per IP address. On a
+shared NAT or CI runner, authenticate those requests to avoid HTTP 403 rate
+limits: export `GH_TOKEN` (or `GITHUB_TOKEN`), or run `gh auth login` inside
+the Box. The token is optional, is sent only to the GitHub API, and a rejected
+token falls back to unauthenticated requests.
+
 ### Full rebuild (from the host)
 
     sqrbx-rebuild
diff --git a/SECURITY.md b/SECURITY.md
index 3701a7e..39d20cc 100644
--- a/SECURITY.md
+++ b/SECURITY.md
@@ -169,6 +169,17 @@ Unsupported architectures and invalid Tool-tier/destination combinations fail
 before network or destination mutation. Extracted archives reject escaping
 links, special files, and ambiguous executable matches before promotion.
 
+GitHub API metadata requests are optionally authenticated to raise the
+unauthenticated rate limit. The token comes from `GH_TOKEN`, then
+`GITHUB_TOKEN`, then an already-authenticated `gh` CLI (`gh auth token`, only
+for the default `https://api.github.com` base; never prompted). It is sent as
+an `Authorization: Bearer` header only to the configured HTTPS API base, never
+to artifact downloads or redirect targets, and reaches curl through a stdin
+config rather than its command line. It is not logged or written to the
+metadata cache. An HTTP 401 drops the token for the rest of that run and
+retries once unauthenticated. Authentication changes only rate limits; it does
+not relax digest verification.
+
 The GitHub CLI and Eza APT repositories are configured only while the image
 builds (then removed). Their signing keys are not trusted on download alone:
 the Dockerfile pins each key's expected full 40-hex primary-key fingerprint set
diff --git a/scripts/lib/tool-lib.sh b/scripts/lib/tool-lib.sh
index 74067e4..eb94ff3 100644
--- a/scripts/lib/tool-lib.sh
+++ b/scripts/lib/tool-lib.sh
@@ -376,8 +376,68 @@ _sb_gh_cache_failure() {
 	/bin/mv -fT -- "$stage" "$path" 2>/dev/null || rm -f -- "$stage" 2>/dev/null || true
 }
 
+# Optional GitHub API authentication raises the unauthenticated 60 requests per
+# hour limit. Precedence: GH_TOKEN, GITHUB_TOKEN, then an already-authenticated
+# gh CLI (evaluated lazily, at most once per shell; never prompts). The token is
+# sent only to the configured HTTPS SB_GITHUB_API_BASE, reaches curl through a
+# stdin config rather than argv, and is never logged or written to the metadata
+# cache. curl does not forward a custom Authorization header to another host
+# when following a redirect.
+_SB_GH_TOKEN=""
+_SB_GH_TOKEN_RESOLVED=false
+_SB_GH_TOKEN_DISABLED=false
+
+_sb_gh_resolve_token() {
+	local token="" source=""
+	[ "$_SB_GH_TOKEN_RESOLVED" = false ] || return 0
+	_SB_GH_TOKEN_RESOLVED=true
+	_SB_GH_TOKEN=""
+	if [ -n "${GH_TOKEN:-}" ]; then
+		token=$GH_TOKEN; source=GH_TOKEN
+	elif [ -n "${GITHUB_TOKEN:-}" ]; then
+		token=$GITHUB_TOKEN; source=GITHUB_TOKEN
+	elif [ "${SB_GITHUB_API_BASE%/}" = "https://api.github.com" ] && command -v gh >/dev/null 2>&1; then
+		# gh's stored credential belongs to github.com; never offer it to a
+		# custom API base. Without a stored login this fails without prompting.
+		token=$(GH_PROMPT_DISABLED=1 gh auth token --hostname github.com </dev/null 2>/dev/null) || token=""
+		source="gh auth token"
+	fi
+	[ -n "$token" ] || return 0
+	# Restrict to token characters so the value cannot alter curl's config.
+	if ! [[ "$token" =~ ^[A-Za-z0-9_.-]+$ ]]; then
+		echo "Warning: ignoring malformed GitHub token from ${source}; using unauthenticated GitHub API requests" >&2
+		return 0
+	fi
+	_SB_GH_TOKEN=$token
+}
+
+# Succeed (with _SB_GH_TOKEN set) only when url targets the configured HTTPS
+# API base and a usable token exists. Runs in the current shell so lazy token
+# resolution is remembered.
+_sb_gh_token_applies() {
+	local url="$1" base="${SB_GITHUB_API_BASE%/}"
+	[ "$_SB_GH_TOKEN_DISABLED" = false ] || return 1
+	[[ "$base" == https://?* ]] || return 1
+	[[ "$url" == "$base/"* ]] || return 1
+	_sb_gh_resolve_token
+	[ -n "$_SB_GH_TOKEN" ]
+}
+
+# One metadata GET. With authentication, the header is supplied through a curl
+# config here-string on stdin so the token never appears in argv or ps output.
+_sb_gh_curl_metadata() {
+	local url="$1" authenticated="$2"
+	if [ "$authenticated" = true ]; then
+		curl -K - -sSL -w '\n%{http_code}' "$url" 2>/dev/null \
+			<<<"header = \"Authorization: Bearer ${_SB_GH_TOKEN}\""
+	else
+		curl -sSL -w '\n%{http_code}' "$url" 2>/dev/null
+	fi
+}
+
 _sb_gh_api_get() {
 	local url="$1" context="$2" response curl_rc http_code body message cache_path failed_path
+	local authenticated=false
 	if [ -n "${_SB_GH_BODY_CACHE[$url]+x}" ]; then
 		SB_GH_API_BODY=${_SB_GH_BODY_CACHE[$url]}
 		printf '%s\n' "$SB_GH_API_BODY"
@@ -400,8 +460,19 @@ _sb_gh_api_get() {
 		_SB_GH_FAILED_CACHE[$url]=1
 		return 1
 	fi
-	response=$(curl -sSL -w '\n%{http_code}' "$url" 2>/dev/null)
+	! _sb_gh_token_applies "$url" || authenticated=true
+	response=$(_sb_gh_curl_metadata "$url" "$authenticated")
 	curl_rc=$?
+	if [ "$authenticated" = true ] && [ "$curl_rc" -eq 0 ] && [ "${response##*$'\n'}" = "401" ]; then
+		# A rejected token must not block public metadata: drop it for the rest
+		# of this shell and retry once without credentials.
+		echo "Warning: GitHub API rejected the configured token (HTTP 401) for ${context}; retrying unauthenticated" >&2
+		_SB_GH_TOKEN_DISABLED=true
+		_SB_GH_TOKEN=""
+		authenticated=false
+		response=$(_sb_gh_curl_metadata "$url" false)
+		curl_rc=$?
+	fi
 	if [ "$curl_rc" -ne 0 ]; then
 		_SB_GH_FAILED_CACHE[$url]=1
 		_sb_gh_cache_failure "$url"
@@ -440,8 +511,10 @@ _sb_gh_api_get() {
 	_SB_GH_FAILED_CACHE[$url]=1
 	_sb_gh_cache_failure "$url"
 	message=$(printf '%s' "$body" | jq -r '.message // empty' 2>/dev/null || true)
-	if [ "$http_code" = "403" ]; then
-		echo "Error: GitHub API returned HTTP 403 for ${context}${message:+: $message} (possible rate limit)" >&2
+	if { [ "$http_code" = "403" ] || [ "$http_code" = "429" ]; } && [ "$authenticated" = false ]; then
+		echo "Error: GitHub API returned HTTP ${http_code} for ${context}${message:+: $message} (possible unauthenticated rate limit; set GH_TOKEN or run 'gh auth login' to raise it)" >&2
+	elif [ "$http_code" = "403" ] || [ "$http_code" = "429" ]; then
+		echo "Error: GitHub API returned HTTP ${http_code} for ${context}${message:+: $message} (possible rate limit)" >&2
 	else
 		echo "Error: GitHub API returned HTTP ${http_code} for ${context}${message:+: $message}" >&2
 	fi
diff --git a/tests/test-tool-lib.sh b/tests/test-tool-lib.sh
index 07961ae..390b2d6 100755
--- a/tests/test-tool-lib.sh
+++ b/tests/test-tool-lib.sh
@@ -421,6 +421,122 @@ if (
 	[ "$(grep -c 'api.test/' "$CACHE_CASE/curl.log")" -eq 1 ]
 ); then ok "release metadata cache survives command substitution and exact-version install"; else not_ok "release metadata cache survives command substitution and exact-version install"; fi
 
+# ── Optional GitHub API authentication ───────────────────────────────
+# The auth mock curl records every argv element and, only when given a config
+# on stdin (-K -), that config. AUTH_STATUS_WITH_TOKEN overrides the API status
+# for authenticated requests (401 fallback). Downloads copy PAYLOAD.
+AUTH_TOKEN_VALUE=ghp_SyntheticSecretToken0123456789
+run_auth_case() {
+	local name=$1 body=$2
+	local case_dir="$TMP/auth-$name"
+	mkdir -p "$case_dir/home" "$case_dir/cache"
+	(
+		unset GH_TOKEN GITHUB_TOKEN
+		export HOME="$case_dir/home" SB_TOOLS_YAML="$REGISTRY" SB_DPKG_ARCH=amd64
+		export SB_GITHUB_API_BASE=https://api.test SB_GH_METADATA_CACHE_DIR="$case_dir/cache"
+		export CASE_DIR="$case_dir" PAYLOAD_HASH
+		source "$REPO_ROOT/scripts/lib/tool-lib.sh"
+		gh() { printf 'gh %s\n' "$*" >> "$CASE_DIR/gh.log"; return 1; }
+		curl() {
+			local output="" url="" config="" arg
+			for arg in "$@"; do printf '%s\n' "$arg" >> "$CASE_DIR/argv.log"; done
+			printf -- '--\n' >> "$CASE_DIR/argv.log"
+			while [ "$#" -gt 0 ]; do
+				case "$1" in
+					-K) [ "$2" = - ] && config=$(cat); shift 2 ;;
+					-w) shift 2 ;;
+					-o) output=$2; shift 2 ;;
+					-*o) output=$2; shift 2 ;;
+					-*) shift ;;
+					*) url=$1; shift ;;
+				esac
+			done
+			printf '%s|%s\n' "$url" "${config:-none}" >> "$CASE_DIR/requests.log"
+			if [[ "$url" == http*://api.test/* || "$url" == https://api.github.com/* ]]; then
+				if [ -n "$config" ] && [ -n "${AUTH_STATUS_WITH_TOKEN:-}" ]; then
+					printf '{"message":"Bad credentials"}\n%s\n' "$AUTH_STATUS_WITH_TOKEN"
+				else
+					printf '{"tag_name":"v1.0.0","assets":[{"name":"sample-1.0.0-amd64","digest":"sha256:%s"}]}\n%s\n' \
+						"$PAYLOAD_HASH" "${API_STATUS:-200}"
+				fi
+			else
+				cp "$PAYLOAD" "$output"
+			fi
+		}
+		eval "$body"
+	) >"$case_dir/out" 2>"$case_dir/err"
+}
+auth_header_line="header = \"Authorization: Bearer $AUTH_TOKEN_VALUE\""
+token_leaked() {
+	local case_dir=$1
+	grep -rqF "$AUTH_TOKEN_VALUE" "$case_dir/argv.log" "$case_dir/cache" "$case_dir/out" "$case_dir/err" 2>/dev/null
+}
+
+if run_auth_case gh-token "export GH_TOKEN=$AUTH_TOKEN_VALUE GITHUB_TOKEN=other_token; sb_install sample latest" \
+	&& grep -qxF "https://api.test/repos/example/sample/releases/latest|$auth_header_line" "$TMP/auth-gh-token/requests.log" \
+	&& [ -x "$TMP/auth-gh-token/home/.local/bin/sample" ]; then
+	ok "GH_TOKEN sends a Bearer Authorization header to the GitHub API"
+else not_ok "GH_TOKEN sends a Bearer Authorization header to the GitHub API"; fi
+
+if ! token_leaked "$TMP/auth-gh-token" && [ -n "$(ls -A "$TMP/auth-gh-token/cache")" ]; then
+	ok "GitHub token is absent from curl argv, output, and the metadata cache"
+else not_ok "GitHub token is absent from curl argv, output, and the metadata cache"; fi
+
+if grep -q '/releases/download/v1.0.0/sample-1.0.0-amd64|none$' "$TMP/auth-gh-token/requests.log" \
+	&& [ "$(grep -c '|none$' "$TMP/auth-gh-token/requests.log")" -eq 1 ]; then
+	ok "GitHub token is never sent with artifact downloads"
+else not_ok "GitHub token is never sent with artifact downloads"; fi
+
+if run_auth_case github-token "export GITHUB_TOKEN=$AUTH_TOKEN_VALUE; sb_gh_latest_tag example/sample >/dev/null" \
+	&& grep -qxF "https://api.test/repos/example/sample/releases/latest|$auth_header_line" "$TMP/auth-github-token/requests.log" \
+	&& [ ! -e "$TMP/auth-github-token/gh.log" ]; then
+	ok "GITHUB_TOKEN authenticates when GH_TOKEN is unset"
+else not_ok "GITHUB_TOKEN authenticates when GH_TOKEN is unset"; fi
+
+if run_auth_case no-token "sb_gh_latest_tag example/sample >/dev/null" \
+	&& grep -qxF 'https://api.test/repos/example/sample/releases/latest|none' "$TMP/auth-no-token/requests.log" \
+	&& ! grep -qx -- '-K' "$TMP/auth-no-token/argv.log" \
+	&& [ ! -e "$TMP/auth-no-token/gh.log" ]; then
+	ok "without a token no Authorization header is sent and gh is not consulted for a custom API base"
+else not_ok "without a token no Authorization header is sent and gh is not consulted for a custom API base"; fi
+
+if run_auth_case plain-http "export GH_TOKEN=$AUTH_TOKEN_VALUE SB_GITHUB_API_BASE=http://api.test; sb_gh_latest_tag example/sample >/dev/null" \
+	&& grep -qxF 'http://api.test/repos/example/sample/releases/latest|none' "$TMP/auth-plain-http/requests.log"; then
+	ok "GitHub token is withheld from a non-HTTPS API base"
+else not_ok "GitHub token is withheld from a non-HTTPS API base"; fi
+
+if run_auth_case fallback-401 "export GH_TOKEN=$AUTH_TOKEN_VALUE AUTH_STATUS_WITH_TOKEN=401
+	sb_gh_latest_tag example/sample >/dev/null && sb_gh_latest_tag example/packed >/dev/null" \
+	&& [ "$(sed -n 1p "$TMP/auth-fallback-401/requests.log")" = "https://api.test/repos/example/sample/releases/latest|$auth_header_line" ] \
+	&& [ "$(sed -n 2p "$TMP/auth-fallback-401/requests.log")" = 'https://api.test/repos/example/sample/releases/latest|none' ] \
+	&& [ "$(sed -n 3p "$TMP/auth-fallback-401/requests.log")" = 'https://api.test/repos/example/packed/releases/latest|none' ] \
+	&& [ "$(wc -l < "$TMP/auth-fallback-401/requests.log")" -eq 3 ] \
+	&& grep -q 'rejected the configured token (HTTP 401).*retrying unauthenticated' "$TMP/auth-fallback-401/err" \
+	&& ! token_leaked "$TMP/auth-fallback-401"; then
+	ok "HTTP 401 with a token retries once unauthenticated, warns, and drops the token"
+else not_ok "HTTP 401 with a token retries once unauthenticated, warns, and drops the token"; fi
+
+if ! run_auth_case rate-limit "export API_STATUS=403; sb_gh_latest_tag example/sample >/dev/null" \
+	&& grep -q "HTTP 403.*set GH_TOKEN or run 'gh auth login'" "$TMP/auth-rate-limit/err"; then
+	ok "unauthenticated HTTP 403 fails closed and suggests GH_TOKEN or gh auth login"
+else not_ok "unauthenticated HTTP 403 fails closed and suggests GH_TOKEN or gh auth login"; fi
+
+if run_auth_case gh-cli "export SB_GITHUB_API_BASE=https://api.github.com
+	gh() { printf 'gh %s\n' \"\$*\" >> \"\$CASE_DIR/gh.log\"; [ \"\$1 \$2\" = 'auth token' ] && printf '%s\n' $AUTH_TOKEN_VALUE; }
+	sb_gh_latest_tag example/sample >/dev/null && sb_gh_latest_tag example/packed >/dev/null" \
+	&& [ "$(wc -l < "$TMP/auth-gh-cli/gh.log")" -eq 1 ] \
+	&& [ "$(grep -cF "|$auth_header_line" "$TMP/auth-gh-cli/requests.log")" -eq 2 ] \
+	&& ! token_leaked "$TMP/auth-gh-cli"; then
+	ok "authenticated gh CLI token is resolved lazily once for the default API base"
+else not_ok "authenticated gh CLI token is resolved lazily once for the default API base"; fi
+
+if run_auth_case malformed-token "export GH_TOKEN='bad\"token'; sb_gh_latest_tag example/sample >/dev/null" \
+	&& grep -qxF 'https://api.test/repos/example/sample/releases/latest|none' "$TMP/auth-malformed-token/requests.log" \
+	&& grep -q 'ignoring malformed GitHub token from GH_TOKEN' "$TMP/auth-malformed-token/err" \
+	&& ! grep -qF 'bad"token' "$TMP/auth-malformed-token/err"; then
+	ok "malformed token is ignored without being printed"
+else not_ok "malformed token is ignored without being printed"; fi
+
 BAD_REGISTRY="$TMP/bad-tools.yaml"
 cp "$REGISTRY" "$BAD_REGISTRY"
 sed -i '0,/method: binary/s//method: shell-pipe/' "$BAD_REGISTRY"