diff --git a/docs/plans/CASAN_BACKLOG_STATUS.md b/docs/plans/CASAN_BACKLOG_STATUS.md
index 10e7031..cca2680 100644
--- a/docs/plans/CASAN_BACKLOG_STATUS.md
+++ b/docs/plans/CASAN_BACKLOG_STATUS.md
@@ -43,6 +43,7 @@
 | T2.5 | Billing-API telemetry thật | 🟡 Docker lab ✅ (billing API mock) | `billing-api` @ `:19093/usage`; `provider-usage-fetch.sh` import được provider telemetry. Prod: OpenAI/Anthropic usage API thật + key. |
 | T2.6 | Sandbox: rootless/nsjail + base image CI | 🟡 (container isolation live via Docker) | Thêm profile nsjail/bubblewrap cho Linux CI (không cần Docker daemon); hardened base image tối thiểu. `sandbox-container.sh` đã có bản Docker. |
 | T2.7 | Backup/restore + restore drill | 🟡 automated + test | `state-backup.sh` creates manifest/hash-bound state snapshots, requires encryption key in prod, restores only to an empty explicit directory; `phase-state-backup` is in CI. Remaining: customer object-store replication, retention/RPO/RTO, and a retained production restore-drill record. |
+| T2.8 | Upgrade/rollback compatibility | 🟡 automated + test | `upgrade-compatibility.sh` is fail-closed and permits only explicit matrix rules; the 1.0.x patch/rollback rule requires provenance, backup, artifact smoke and post-deploy Evidence Pack verification. Remaining: a reviewed migration rule for every future minor/major release and a retained live rollout/rollback record. |
 
 ## TIER 3 — Platform plans (INDEX 01–12, việc lớn nhiều phiên) 📋
 
diff --git a/infra/production/UPGRADE_ROLLBACK.md b/infra/production/UPGRADE_ROLLBACK.md
new file mode 100644
index 0000000..9aad9db
--- /dev/null
+++ b/infra/production/UPGRADE_ROLLBACK.md
@@ -0,0 +1,18 @@
+# Upgrade and Rollback Runbook
+
+The compatibility gate is mandatory before every deployment or rollback:
+
+```bash
+bash packages/casan-harness/scripts/bash/upgrade-compatibility.sh check \
+  --from 1.0.0 --to 1.0.1
+```
+
+Only an explicit rule in `compatibility-matrix.json` can permit a version pair.
+Before rollout, verify provenance, create and verify a state backup, smoke the
+extracted artifact, deploy immutable image digests, and verify an Evidence Pack
+after deployment. A rollback requires the same gate with `--rollback`, plus an
+approved change record and a verified backup.
+
+Do not infer compatibility from matching image tags, passing unit tests, or
+successful container startup. Add and review a new matrix entry before any
+cross-minor or cross-major migration.
diff --git a/infra/production/compatibility-matrix.json b/infra/production/compatibility-matrix.json
new file mode 100644
index 0000000..75ecb10
--- /dev/null
+++ b/infra/production/compatibility-matrix.json
@@ -0,0 +1,18 @@
+{
+  "schema_version": "1.0",
+  "product": "CASAN",
+  "rules": [
+    {
+      "from": "1.0.x",
+      "to": "1.0.x",
+      "policy_schema": "1",
+      "evidence_pack_schema": "1.0-mvp",
+      "rollback": "supported",
+      "notes": "Patch-level upgrades only. Back up runtime state and verify the candidate artifact before rollout."
+    }
+  ],
+  "unsupported": [
+    "Cross-major upgrades require a reviewed migration entry before deployment.",
+    "Downgrades that change policy or Evidence Pack schema are denied until an explicit rollback entry is added."
+  ]
+}
diff --git a/packages/casan-harness/scripts/bash/ci-harness-gate.sh b/packages/casan-harness/scripts/bash/ci-harness-gate.sh
index 3e300e5..93afb4b 100755
--- a/packages/casan-harness/scripts/bash/ci-harness-gate.sh
+++ b/packages/casan-harness/scripts/bash/ci-harness-gate.sh
@@ -138,6 +138,7 @@ run "phase-sec24-supplychain"    bash "$TESTS/phase-sec24-tests.sh"
 run "phase-sec25-attestation"    bash "$TESTS/phase-sec25-tests.sh"
 run "phase-production-handoff"   bash "$TESTS/phase-production-preflight-tests.sh"
 run "phase-state-backup"         bash "$TESTS/phase-state-backup-tests.sh"
+run "phase-upgrade-compatibility" bash "$TESTS/phase-upgrade-compatibility-tests.sh"
 run "phase-release-provenance"    bash "$TESTS/phase-release-provenance-tests.sh"
 run "phase-service-desk-onboard"  bash "$TESTS/phase-service-desk-onboard-tests.sh"
 
diff --git a/packages/casan-harness/scripts/bash/upgrade-compatibility.sh b/packages/casan-harness/scripts/bash/upgrade-compatibility.sh
new file mode 100755
index 0000000..8a2b92b
--- /dev/null
+++ b/packages/casan-harness/scripts/bash/upgrade-compatibility.sh
@@ -0,0 +1,56 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+# Fail-closed compatibility gate for an upgrade or rollback. This command does
+# not deploy. It produces a machine-readable plan that a release workflow must
+# verify before it changes runtime state.
+#
+# upgrade-compatibility.sh check --from 1.0.0 --to 1.0.1 [--matrix FILE]
+# upgrade-compatibility.sh check --from 1.0.1 --to 1.0.0 --rollback [--matrix FILE]
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+source "$SCRIPT_DIR/casan-paths.sh"
+CMD="${1:-}"; shift || true
+FROM=""; TO=""; ROLLBACK=false
+MATRIX="${CASAN_COMPATIBILITY_MATRIX:-$CASAN_APP_ROOT/infra/production/compatibility-matrix.json}"
+while [[ "$#" -gt 0 ]]; do
+  case "$1" in
+    --from) FROM="${2:-}"; shift 2 ;;
+    --to) TO="${2:-}"; shift 2 ;;
+    --matrix) MATRIX="${2:-}"; shift 2 ;;
+    --rollback) ROLLBACK=true; shift ;;
+    *) echo "UPGRADE_COMPATIBILITY_FAIL reason=unknown_option option=$1" >&2; exit 64 ;;
+  esac
+done
+[[ "$CMD" == "check" && -n "$FROM" && -n "$TO" && -f "$MATRIX" ]] || {
+  echo "Usage: upgrade-compatibility.sh check --from X.Y.Z --to X.Y.Z [--rollback] [--matrix FILE]" >&2; exit 64; }
+
+python3 - "$MATRIX" "$FROM" "$TO" "$ROLLBACK" <<'PY'
+import json, re, sys
+matrix, source, target, rollback = sys.argv[1:]
+def parse(v):
+    m = re.fullmatch(r'(\d+)\.(\d+)\.(\d+)', v)
+    if not m: raise ValueError('invalid_semver')
+    return tuple(map(int, m.groups()))
+try:
+    src, dst = parse(source), parse(target)
+    data = json.load(open(matrix, encoding='utf8'))
+except Exception as e:
+    print(f'UPGRADE_COMPATIBILITY_FAIL reason={str(e)[:80]}', file=sys.stderr); raise SystemExit(1)
+def matches(pattern, version):
+    m = re.fullmatch(r'(\d+)\.(\d+)\.(x|\d+)', pattern)
+    if not m: return False
+    a,b,c=m.groups()
+    return version[0] == int(a) and version[1] == int(b) and (c == 'x' or version[2] == int(c))
+for rule in data.get('rules', []):
+    if matches(str(rule.get('from','')), src) and matches(str(rule.get('to','')), dst):
+        if rollback == 'true' and rule.get('rollback') != 'supported':
+            continue
+        print(json.dumps({'decision':'allow','from':source,'to':target,'rollback':rollback == 'true',
+                          'policy_schema':rule.get('policy_schema'),'evidence_pack_schema':rule.get('evidence_pack_schema'),
+                          'required_steps':['verify_release_provenance','state_backup','artifact_smoke','post_deploy_evidence_verify']}, sort_keys=True))
+        raise SystemExit(0)
+print(json.dumps({'decision':'deny','from':source,'to':target,'rollback':rollback == 'true',
+                  'reason':'no_approved_compatibility_rule'}, sort_keys=True), file=sys.stderr)
+raise SystemExit(1)
+PY
diff --git a/packages/casan-harness/tests/phase-upgrade-compatibility-tests.sh b/packages/casan-harness/tests/phase-upgrade-compatibility-tests.sh
new file mode 100755
index 0000000..e885995
--- /dev/null
+++ b/packages/casan-harness/tests/phase-upgrade-compatibility-tests.sh
@@ -0,0 +1,13 @@
+#!/usr/bin/env bash
+set -uo pipefail
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+source "$SCRIPT_DIR/../scripts/bash/casan-paths.sh"
+S="$CASAN_HARNESS_ROOT/scripts/bash/upgrade-compatibility.sh"
+M="$CASAN_APP_ROOT/infra/production/compatibility-matrix.json"
+PASS=0; FAIL=0
+pass(){ echo "PASS: $1"; PASS=$((PASS+1)); }; fail(){ echo "FAIL: $1"; FAIL=$((FAIL+1)); }
+if bash "$S" check --from 1.0.0 --to 1.0.1 --matrix "$M" | grep -q '"decision": "allow"'; then pass "patch upgrade is explicitly allowed"; else fail "patch upgrade denied"; fi
+if bash "$S" check --from 1.0.1 --to 1.0.0 --rollback --matrix "$M" | grep -q '"rollback": true'; then pass "approved rollback is explicitly allowed"; else fail "approved rollback denied"; fi
+if bash "$S" check --from 1.0.1 --to 2.0.0 --matrix "$M" >/dev/null 2>&1; then fail "unreviewed major upgrade accepted"; else pass "unreviewed major upgrade denied"; fi
+if bash "$S" check --from invalid --to 1.0.0 --matrix "$M" >/dev/null 2>&1; then fail "invalid version accepted"; else pass "invalid version denied"; fi
+echo "===== UPGRADE COMPATIBILITY SUMMARY: PASS=$PASS FAIL=$FAIL ====="; [[ "$FAIL" -eq 0 ]]