diff --git a/.fusa-reqs.json b/.fusa-reqs.json
index 970cb4c..533cf5a 100644
--- a/.fusa-reqs.json
+++ b/.fusa-reqs.json
@@ -852,7 +852,7 @@
     {
       "id": "REQ-RELAY-001",
       "title": "Protocol enum values are defined and stable",
-      "description": "relay::Protocol shall define CAN=1, DDS=2, LIN=3, MQTT=4, RCP=5, SOMEIP=6 as stable integer values matching RELAY spec v1.10 §3.",
+      "description": "relay::Protocol shall define CAN=1, DDS=2, LIN=3, MQTT=4, RCP=5, SOMEIP=6 as stable integer values matching RELAY spec v1.11 §3.",
       "asil": "ASIL-B",
       "rationale": "Protocol values are wire-format identifiers; changing them breaks cross-language interop.",
       "tags": ["relay", "protocol"]
@@ -1003,8 +1003,8 @@
     },
     {
       "id": "REQ-RELAY-020",
-      "title": "kSpecVersion constant equals '1.10'",
-      "description": "relay::kSpecVersion shall be a constexpr const char* equal to '1.10'.",
+      "title": "kSpecVersion constant equals '1.11'",
+      "description": "relay::kSpecVersion shall be a constexpr const char* equal to '1.11'.",
       "asil": "ASIL-B",
       "rationale": "RELAY §2: spec version constant enables runtime conformance checking.",
       "tags": ["relay", "version"]
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 1e6aa4e..e69f502 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -65,7 +65,9 @@ endif()
 # ── CLI binary ────────────────────────────────────────────────────────────────
 
 option(CPPLIN_BUILD_CLI "Build RELAY convert CLI" ON)
-if(CPPLIN_BUILD_CLI)
+# RELAY spec v1.11 §17.7: C++ implementations must be buildable via -DRELAY_BUILD_CLI=ON
+option(RELAY_BUILD_CLI "Alias for CPPLIN_BUILD_CLI (RELAY spec §17.7)" OFF)
+if(CPPLIN_BUILD_CLI OR RELAY_BUILD_CLI)
     add_subdirectory(cli)
 endif()
 
diff --git a/HARA.md b/HARA.md
index b690af0..05ee1da 100644
--- a/HARA.md
+++ b/HARA.md
@@ -131,6 +131,6 @@ ASIL-D at system level if required.
 
 - ISO 26262:2018 Part 3 — Concept phase
 - LIN Specification Package Rev 2.2A — Section 2 (Frame structure)
-- RELAY Specification v1.10 — §15 (Error handling)
+- RELAY Specification v1.11 — §15 (Error handling)
 - `SEOOC.md` — Assumptions on use
 - `SAFETY_PLAN.md` — Development process
diff --git a/INCIDENT-RESPONSE.md b/INCIDENT-RESPONSE.md
index 2218f0b..a0a6367 100644
--- a/INCIDENT-RESPONSE.md
+++ b/INCIDENT-RESPONSE.md
@@ -125,6 +125,6 @@ For safety-critical (ASIL-B) vulnerabilities, the following additional steps app
 - **ISO/SAE 21434:2021** §7.4 — Vulnerability management and disclosure
 - **IEC 62443-4-1:2018** SM-2 — Security management (vulnerability response)
 - **IEC/TR 62443-2-3:2015** — Patch management for IACS
-- **RELAY Spec v1.10** §22 — Security considerations
+- **RELAY Spec v1.11** §22 — Security considerations
 - `SECURITY.md` — Public-facing vulnerability disclosure policy
 - `SEOOC.md` — Safety Element out of Context assumptions (integrator scope)
diff --git a/README.md b/README.md
index 845a2e6..f952427 100644
--- a/README.md
+++ b/README.md
@@ -3,14 +3,14 @@
 C++ LIN bus library — RELAY-conformant, ISO 26262 ASIL-B.
 
 [![CI](https://github.com/SoundMatt/cpp-LIN/actions/workflows/ci.yml/badge.svg)](https://github.com/SoundMatt/cpp-LIN/actions/workflows/ci.yml)
-[![RELAY Conformant](https://img.shields.io/badge/RELAY-v1.10%20conformant-blue)](https://github.com/SoundMatt/RELAY)
+[![RELAY Conformant](https://img.shields.io/badge/RELAY-v1.11%20conformant-blue)](https://github.com/SoundMatt/RELAY)
 [![ASIL-B](https://img.shields.io/badge/ISO%2026262-ASIL--B-orange)](SAFETY_PLAN.md)
 [![License: MPL 2.0](https://img.shields.io/badge/License-MPL%202.0-brightgreen.svg)](LICENSE)
 
 ## Overview
 
 cpp-LIN is a production-quality C++ implementation of the LIN (Local Interconnect
-Network) protocol, following the RELAY specification v1.10. It is the C++ sibling
+Network) protocol, following the RELAY specification v1.11. It is the C++ sibling
 of [go-LIN](https://github.com/SoundMatt/go-LIN) and is patterned after
 [cpp-CAN](https://github.com/SoundMatt/cpp-CAN).
 
@@ -49,7 +49,7 @@ ctest --test-dir build --output-on-failure
 ```
 include/lin/
   channel.hpp        — Chan<T>: bounded, thread-safe FIFO
-  relay.hpp          — RELAY v1.10 types (Protocol, Message, INode, …)
+  relay.hpp          — RELAY v1.11 types (Protocol, Message, INode, …)
   lin.hpp            — IBus, IMasterBus, Frame, Filter, free functions
   virtual/bus.hpp    — In-process virtual LIN bus
   safety/e2e.hpp     — E2E Protector / Receiver
@@ -95,7 +95,7 @@ P1 = NOT(ID1 ^ ID3 ^ ID4 ^ ID5)   (bit 7)
 
 ## RELAY Integration
 
-cpp-LIN exposes a RELAY v1.10 `INode` adapter:
+cpp-LIN exposes a RELAY v1.11 `INode` adapter:
 
 ```cpp
 #include <lin/lin.hpp>
diff --git a/ROADMAP.md b/ROADMAP.md
index e0787ff..2782728 100644
--- a/ROADMAP.md
+++ b/ROADMAP.md
@@ -8,7 +8,7 @@
 - [x] Master node with schedule table runner (`std::stop_token`)
 - [x] Slave node with per-ID response registration
 - [x] E2E safety: Protector and Receiver (CRC-16/CCITT-FALSE, 10-byte header)
-- [x] RELAY v1.10 adapter (`relay::INode`)
+- [x] RELAY v1.11 adapter (`relay::INode`)
 - [x] CLI binary (`cpp-lin-cli`) for relay conform/interop
 - [x] ISO 26262 ASIL-B requirements traceability
 - [x] CI pipeline: build, test, coverage, sanitizers, RELAY conform, cpfusa
diff --git a/SAFETY_MANUAL.md b/SAFETY_MANUAL.md
index 11a2031..b1159fb 100644
--- a/SAFETY_MANUAL.md
+++ b/SAFETY_MANUAL.md
@@ -245,7 +245,7 @@ must ensure:
 4. The `id` field in `relay::Message` carries the decimal string representation
    of the LIN frame ID (e.g., `"16"` for frame 0x10).
 
-See `RELAY Spec v1.10 §8.3` for the complete LIN-over-RELAY envelope specification.
+See `RELAY Spec v1.11 §8.3` for the complete LIN-over-RELAY envelope specification.
 
 ---
 
@@ -290,4 +290,4 @@ Reproducing from `SEOOC.md` for convenience:
 - `sas.md` — Software Architecture Specification
 - ISO 26262:2018 Part 6 §7 — Software integration and verification
 - ISO 26262:2018 Part 10 §9 — Safety element out of context
-- RELAY Specification v1.10 §8.3 — LIN bus binding
+- RELAY Specification v1.11 §8.3 — LIN bus binding
diff --git a/SAFETY_PLAN.md b/SAFETY_PLAN.md
index f8e2b15..c5278b9 100644
--- a/SAFETY_PLAN.md
+++ b/SAFETY_PLAN.md
@@ -13,7 +13,7 @@
 
 This Safety Plan governs the development of **cpp-LIN**, a C++ software
 component implementing the LIN (Local Interconnect Network) bus protocol,
-conformant to the RELAY specification v1.10.
+conformant to the RELAY specification v1.11.
 
 cpp-LIN is classified as a **Safety Element out of Context (SEooC)** per
 ISO 26262-10 §9. It is intended for integration into automotive ECUs and
@@ -131,7 +131,7 @@ See [HARA.md](HARA.md).
 - IEC 61508:2010 — Functional safety of E/E/PE safety-related systems
 - ISO/SAE 21434:2021 — Road vehicles — Cybersecurity engineering
 - LIN Specification Package, Revision 2.2A (LIN Consortium)
-- RELAY Specification v1.10 (SoundMatt)
+- RELAY Specification v1.11 (SoundMatt)
 - `.fusa-reqs.json` — Machine-readable requirements
 - `HARA.md` — Hazard Analysis and Risk Assessment
 - `SEOOC.md` — Safety Element out of Context document
diff --git a/SECURITY.md b/SECURITY.md
index 51093df..0dfd0d0 100644
--- a/SECURITY.md
+++ b/SECURITY.md
@@ -67,4 +67,4 @@ escalation contacts.
 
 - ISO/SAE 21434:2021 §7.4 — Vulnerability management
 - IEC 62443-4-1:2018 SM-2 — Security management
-- RELAY Spec v1.10 §22 — Security considerations
+- RELAY Spec v1.11 §22 — Security considerations
diff --git a/cli/json.hpp b/cli/json.hpp
index ad18916..727b9a5 100644
--- a/cli/json.hpp
+++ b/cli/json.hpp
@@ -177,7 +177,7 @@ inline std::string version_json() {
            "\"protocol\":\"LIN\","
            "\"protocol_int\":3,"
            "\"version\":\"0.1.0\","
-           "\"spec_version\":\"1.10\","
+           "\"spec_version\":\"1.11\","
            "\"language\":\"cpp\","
            "\"runtime\":\"c++17\""
            "}";
@@ -191,7 +191,7 @@ inline std::string capabilities_json() {
            "\"protocol\":\"LIN\","
            "\"protocol_int\":3,"
            "\"version\":\"0.1.0\","
-           "\"spec_version\":\"1.10\","
+           "\"spec_version\":\"1.11\","
            "\"commands\":[\"version\",\"capabilities\",\"status\",\"convert\"],"
            "\"transports\":[\"LIN\"],"
            "\"features\":[\"ldf\",\"e2e\",\"master\",\"slave\",\"virtual\"],"
diff --git a/include/lin/lin.hpp b/include/lin/lin.hpp
index 3bea917..1610b1e 100644
--- a/include/lin/lin.hpp
+++ b/include/lin/lin.hpp
@@ -28,7 +28,7 @@ namespace lin {
 
 // ── Spec version ─────────────────────────────────────────────────────────────
 
-inline constexpr const char* kSpecVersion = "1.10";
+inline constexpr const char* kSpecVersion = "1.11";
 
 // ── Constants ─────────────────────────────────────────────────────────────────
 
diff --git a/include/lin/relay.hpp b/include/lin/relay.hpp
index 782538a..1b061d0 100644
--- a/include/lin/relay.hpp
+++ b/include/lin/relay.hpp
@@ -4,7 +4,7 @@
 // file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 // relay.hpp — RELAY spec types shared across all protocol implementations.
-// Mirrors the RELAY Go package spec v1.10.
+// Mirrors the RELAY Go package spec v1.11.
 
 #pragma once
 
@@ -24,7 +24,7 @@ namespace relay {
 // ── Spec version ─────────────────────────────────────────────────────────────
 
 // fusa:req REQ-RELAY-020
-inline constexpr const char* kSpecVersion = "1.10";
+inline constexpr const char* kSpecVersion = "1.11";
 
 // ── Protocol ─────────────────────────────────────────────────────────────────
 
diff --git a/requirements/requirements.json b/requirements/requirements.json
index 1bd7d8e..03121d6 100644
--- a/requirements/requirements.json
+++ b/requirements/requirements.json
@@ -5,7 +5,7 @@
     "language": "cpp",
     "standard": "iso26262",
     "asil": "ASIL-B",
-    "spec": "RELAY v1.10"
+    "spec": "RELAY v1.11"
   },
   "requirements": [
     {"id": "REQ-LIN-001",  "title": "ValidateFrame rejects ID > 0x3F",                  "asil": "ASIL-B", "tags": ["core", "validation"]},
diff --git a/sas.md b/sas.md
index 03459b4..b196940 100644
--- a/sas.md
+++ b/sas.md
@@ -272,7 +272,7 @@ class Node {
 - `SubscriberOption` / `SubscriberConfig` / `apply_options()`
 - `INode`, `ICaller` abstract interfaces
 - Optional capability interfaces: `IHealthProvider`, `IMetricsProvider`, `IDrainer`
-- kSpecVersion constant "1.10"
+- kSpecVersion constant "1.11"
 
 **Requirements:** REQ-RELAY-001..029, REQ-RELAY-051, REQ-RELAY-056, REQ-RELAY-059
 
diff --git a/testdata/relay-vectors/errors/lin-diagnostic-wrong-checksum.json b/testdata/relay-vectors/errors/lin-diagnostic-wrong-checksum.json
index f85eb51..5895c60 100644
--- a/testdata/relay-vectors/errors/lin-diagnostic-wrong-checksum.json
+++ b/testdata/relay-vectors/errors/lin-diagnostic-wrong-checksum.json
@@ -7,7 +7,7 @@
     "lin.checksum": "99",
     "lin.checksum_type": "1"
   },
-  "spec_version": "1.10",
+  "spec_version": "1.11",
   "expected_error": "ErrInvalidFrame",
   "error_reason": "diagnostic frames (0x3C/0x3D) must use Classic checksum (type 0)"
 }
diff --git a/testdata/relay-vectors/errors/lin-id-overflow.json b/testdata/relay-vectors/errors/lin-id-overflow.json
index b3c75aa..b5e6096 100644
--- a/testdata/relay-vectors/errors/lin-id-overflow.json
+++ b/testdata/relay-vectors/errors/lin-id-overflow.json
@@ -7,7 +7,7 @@
     "lin.checksum": "0",
     "lin.checksum_type": "1"
   },
-  "spec_version": "1.10",
+  "spec_version": "1.11",
   "expected_error": "ErrInvalidFrame",
   "error_reason": "LIN frame ID must be in range 0x00–0x3F (max 63); 64 overflows the 6-bit field"
 }
diff --git a/testdata/relay-vectors/lin-frame.json b/testdata/relay-vectors/lin-frame.json
index b97580b..da4aefd 100644
--- a/testdata/relay-vectors/lin-frame.json
+++ b/testdata/relay-vectors/lin-frame.json
@@ -7,5 +7,5 @@
     "lin.checksum": "73",
     "lin.checksum_type": "1"
   },
-  "spec_version": "1.10"
+  "spec_version": "1.11"
 }