diff --git a/lib/model-check.sh b/lib/model-check.sh
new file mode 100644
index 0000000..1cd3cf5
--- /dev/null
+++ b/lib/model-check.sh
@@ -0,0 +1,33 @@
+#!/usr/bin/env bash
+# lib/model-check.sh — classify the persisted session model: big | small | unknown
+#
+# Witness for lib/model-gate.md (reflection requires a big model). Reads the
+# "model" key of the user-scope settings (the file /model rewrites — LRN-098).
+# Override the source with MODEL_CHECK_SETTINGS (tests use fixtures).
+#
+# stdout : <class>:<raw>   (raw = value found, empty if none)
+# exit   : 0 = big (fable/opus) · 2 = small (sonnet/haiku) · 3 = unknown
+set -u
+
+SETTINGS="${MODEL_CHECK_SETTINGS:-$HOME/.claude/settings.json}"
+
+raw=""
+if [ -f "$SETTINGS" ]; then
+  raw="$(python3 - "$SETTINGS" 2>/dev/null <<'PY'
+import json, sys
+try:
+    v = json.load(open(sys.argv[1])).get("model", "")
+    print(v if isinstance(v, str) else "")
+except Exception:
+    print("")
+PY
+)"
+fi
+
+norm="$(printf '%s' "$raw" | tr '[:upper:]' '[:lower:]')"
+case "$norm" in
+  *opusplan*)       printf 'unknown:%s\n' "$raw"; exit 3 ;; # opus-for-plan, sonnet otherwise — ambiguous
+  *fable*|*opus*)   printf 'big:%s\n'     "$raw"; exit 0 ;;
+  *sonnet*|*haiku*) printf 'small:%s\n'   "$raw"; exit 2 ;;
+  *)                printf 'unknown:%s\n' "$raw"; exit 3 ;;
+esac
diff --git a/lib/tests/model-check.test.sh b/lib/tests/model-check.test.sh
new file mode 100644
index 0000000..040a8f5
--- /dev/null
+++ b/lib/tests/model-check.test.sh
@@ -0,0 +1,25 @@
+#!/usr/bin/env bash
+# lib/tests/model-check.test.sh — flip-tests for lib/model-check.sh (LRN-096)
+set -u
+S="$(cd "$(dirname "$0")/../.." && pwd)/lib/model-check.sh"
+pass=0; fail=0
+check() { if [ "$2" = "$3" ]; then pass=$((pass+1)); else fail=$((fail+1));
+  printf 'FAIL %s: got[%s] want[%s]\n' "$1" "$2" "$3"; fi; }
+T="$(mktemp -d)"; trap 'rm -rf "$T"' EXIT
+
+fx()  { printf '{"model": "%s"}' "$1" > "$T/s.json"; }
+run() { MODEL_CHECK_SETTINGS="$T/s.json" bash "$S" >"$T/out" 2>&1; echo "$?"; }
+
+fx 'claude-fable-5[1m]';        check T1-fable-exit "$(run)" 0
+check T1-fable-class "$(cut -d: -f1 <"$T/out")" big
+fx 'claude-opus-4-8';           check T2-opus       "$(run)" 0
+fx 'claude-sonnet-5';           check T3-sonnet     "$(run)" 2
+fx 'claude-haiku-4-5-20251001'; check T4-haiku      "$(run)" 2
+fx 'opusplan';                  check T5-opusplan   "$(run)" 3
+fx 'gpt-9-mega';                check T6-foreign    "$(run)" 3
+printf '{"no_model": true}' > "$T/s.json"; check T7-no-key    "$(run)" 3
+printf '{broken'            > "$T/s.json"; check T8-malformed "$(run)" 3
+check T9-missing-file "$(MODEL_CHECK_SETTINGS="$T/absent.json" bash "$S" >/dev/null 2>&1; echo $?)" 3
+
+printf 'model-check: %d pass, %d fail\n' "$pass" "$fail"
+[ "$fail" -eq 0 ]