diff --git a/TEST_SUITE_MODERNIZATION_PLAN.md b/TEST_SUITE_MODERNIZATION_PLAN.md
index 8bd8c5dc..036b830d 100644
--- a/TEST_SUITE_MODERNIZATION_PLAN.md
+++ b/TEST_SUITE_MODERNIZATION_PLAN.md
@@ -1,9 +1,9 @@
 # WebSocket-Node Test Suite Modernization Plan
 
-**Status:** 88% Complete ✅
+**Status:** 91% Complete ✅
 **Last Updated:** October 6, 2025
-**Current Phase:** Phases 1-4 Complete + Phase 5 Browser Testing - Coverage Target Achieved
-**Latest Milestone:** Browser Testing Infrastructure Complete (628 total tests, 85.05% overall coverage)
+**Current Phase:** Phases 1-4 Complete + Phase 5 Browser Testing + Phase 6 Multi-Version CI
+**Latest Milestone:** Multi-Version Node.js Testing Complete (18.x, 20.x, 22.x all passing)
 
 ---
 
@@ -36,7 +36,7 @@ This document tracks the comprehensive modernization of the WebSocket-Node test
 
 ## Current Status
 
-### Overall Progress: 88% Complete ✅
+### Overall Progress: 91% Complete ✅
 
 ```
 Phase 1: Foundation Setup             ✅ 100% Complete
@@ -44,7 +44,7 @@ Phase 2: Test Migration & Helpers     ✅ 100% Complete
 Phase 3: Component Testing            ✅ 100% Complete (Coverage target achieved!)
 Phase 4: Integration Testing          ✅ 100% Complete
 Phase 5: E2E Testing                  ✅  70% Complete (Autobahn + Browser Testing)
-Phase 6: CI/CD Optimization           ✅  50% Complete (GitHub Actions + Autobahn)
+Phase 6: CI/CD Optimization           ✅  75% Complete (Multi-Version Testing)
 ```
 
 ### Test Execution Status
@@ -754,11 +754,11 @@ test/
 
 ---
 
-## ✅ Phase 6: CI/CD Optimization - 50% COMPLETE
+## ✅ Phase 6: CI/CD Optimization - 75% COMPLETE
 
-**Status:** GitHub Actions with Protocol Testing
+**Status:** GitHub Actions with Multi-Version Testing
 **Priority:** LOW
-**Completion Date:** October 6, 2025 (Autobahn CI integration)
+**Completion Date:** October 6, 2025 (Autobahn CI + Multi-Version Testing)
 
 ### ✅ 6.1 GitHub Actions CI Pipeline - COMPLETE
 
@@ -788,12 +788,26 @@ test/
 - [ ] Regression alerts
 - [ ] Historical performance tracking
 
-### 6.4 Multi-Version Testing - NOT STARTED
+### ✅ 6.4 Multi-Version Testing - COMPLETE
 
-**Needed:**
-- [ ] Node.js version matrix (16.x, 18.x, 20.x, 22.x)
-- [ ] Parallel test execution in CI
-- [ ] Test result aggregation
+**Status:** Complete
+**Completion Date:** October 6, 2025
+
+**Implemented:**
+- ✅ Node.js version matrix testing (18.x, 20.x, 22.x)
+- ✅ Parallel test execution in CI (fail-fast: false)
+- ✅ Test result aggregation via GitHub Actions
+- ✅ All 628 unit/integration tests run on each version
+- ✅ Autobahn protocol compliance tests (517 tests) on each version
+
+**Node.js versions tested:**
+- Node.js 18.x (Active LTS) - ✅ All tests passing
+- Node.js 20.x (Active LTS) - ✅ All tests passing
+- Node.js 22.x (Current) - ✅ All tests passing
+
+**Note:** Node.js 16.x excluded due to EOL status (September 2023) and Vitest/Vite compatibility issues with crypto APIs.
+
+**File:** `.github/workflows/websocket-tests.yml`
 
 ---
 
@@ -1012,19 +1026,20 @@ Lines:           85.05% ✅
 
 ## Quick Reference
 
-**Current Phase:** E2E Testing - Browser Compatibility
-**Current Sprint:** Complete Phase 5 & Phase 6 remaining items
+**Current Phase:** CI/CD Optimization - Multi-Version Testing
+**Current Sprint:** Complete Phase 6 remaining items (Coverage reporting, Performance benchmarks)
 **Tests Passing:** 1,145/1,145 (100%) - 616 unit + 35 integration + 12 browser + 517 Autobahn
 **Coverage:** 85.05% overall (Target: 85%+) ✅ **ACHIEVED**
-**Next Milestone:** Complete CI/CD optimization, finalize v2.0 release preparation
-**Estimated Completion:** 1-2 weeks
+**Next Milestone:** Coverage reporting integration, finalize v2.0 release preparation
+**Estimated Completion:** 1 week
 
 **Recent Achievements:**
-- ✅ All 628 tests passing (616 unit/integration + 12 browser)
+- ✅ Multi-version Node.js testing (18.x, 20.x, 22.x all passing)
+- ✅ All 628 tests passing across all Node.js versions
 - ✅ Playwright browser testing infrastructure complete
 - ✅ 85%+ coverage target achieved (85.05%)
 - ✅ Autobahn protocol compliance (517 tests, 100% pass rate)
-- ✅ GitHub Actions CI with Autobahn integration
+- ✅ GitHub Actions CI with parallel matrix testing
 - ✅ Cross-platform Docker support
 
 ---