diff --git a/.env.example b/.env.example
index cd364d6..5ee0f86 100644
--- a/.env.example
+++ b/.env.example
@@ -37,9 +37,11 @@ MCP_SERVER_HOST=localhost
 # Server mode: stdio (local) or http (remote)
 MCP_MODE=stdio
 
-# Use fixed HTTP implementation (recommended for stability)
-# Set to true to bypass StreamableHTTPServerTransport issues
-USE_FIXED_HTTP=true
+# DEPRECATED: USE_FIXED_HTTP is deprecated as of v2.31.7
+# The fixed HTTP implementation does not support SSE streaming required by
+# clients like OpenAI Codex. Use the default SingleSessionHTTPServer instead.
+# See: https://github.com/czlonkowski/n8n-mcp/issues/524
+# USE_FIXED_HTTP=true  # DO NOT USE - deprecated
 
 # HTTP Server Configuration (only used when MCP_MODE=http)
 PORT=3000
diff --git a/Dockerfile.railway b/Dockerfile.railway
index 5f51442..39ddf16 100644
--- a/Dockerfile.railway
+++ b/Dockerfile.railway
@@ -74,7 +74,8 @@ ENV AUTH_TOKEN="REPLACE_THIS_AUTH_TOKEN_32_CHARS_MIN_abcdefgh"
 ENV NODE_ENV=production
 ENV IS_DOCKER=true
 ENV MCP_MODE=http
-ENV USE_FIXED_HTTP=true
+# NOTE: USE_FIXED_HTTP is deprecated and removed. SingleSessionHTTPServer is now the default.
+# See: https://github.com/czlonkowski/n8n-mcp/issues/524
 ENV LOG_LEVEL=info
 ENV TRUST_PROXY=1
 ENV HOST=0.0.0.0
diff --git a/docker-compose.yml b/docker-compose.yml
index f6e1d2a..cca6a31 100644
--- a/docker-compose.yml
+++ b/docker-compose.yml
@@ -12,7 +12,8 @@ services:
     environment:
       # Mode configuration
       MCP_MODE: ${MCP_MODE:-http}
-      USE_FIXED_HTTP: ${USE_FIXED_HTTP:-true}  # Use fixed implementation for stability
+      # NOTE: USE_FIXED_HTTP is deprecated and removed. SingleSessionHTTPServer is now the default.
+      # See: https://github.com/czlonkowski/n8n-mcp/issues/524
       AUTH_TOKEN: ${AUTH_TOKEN:?AUTH_TOKEN is required for HTTP mode}
       
       # Application settings
diff --git a/docs/DOCKER_README.md b/docs/DOCKER_README.md
index 8273192..f8b477e 100644
--- a/docs/DOCKER_README.md
+++ b/docs/DOCKER_README.md
@@ -21,7 +21,6 @@ cd n8n-mcp
 # Create .env file with auth token
 cat > .env << EOF
 AUTH_TOKEN=$(openssl rand -base64 32)
-USE_FIXED_HTTP=true
 EOF
 
 # Start the server
@@ -46,7 +45,6 @@ docker pull ghcr.io/czlonkowski/n8n-mcp:latest
 docker run -d \
   --name n8n-mcp \
   -e MCP_MODE=http \
-  -e USE_FIXED_HTTP=true \
   -e AUTH_TOKEN=your-secure-token \
   -p 3000:3000 \
   ghcr.io/czlonkowski/n8n-mcp:latest
diff --git a/docs/HTTP_DEPLOYMENT.md b/docs/HTTP_DEPLOYMENT.md
index 9c0560d..575d494 100644
--- a/docs/HTTP_DEPLOYMENT.md
+++ b/docs/HTTP_DEPLOYMENT.md
@@ -67,7 +67,6 @@ Claude Desktop → mcp-remote → https://your-server.com
 # 1. Create environment file
 cat > .env << EOF
 AUTH_TOKEN=$(openssl rand -base64 32)
-USE_FIXED_HTTP=true
 MCP_MODE=http
 PORT=3000
 # Optional: Enable n8n management tools
@@ -106,7 +105,6 @@ npm run rebuild
 
 # 2. Configure environment
 export MCP_MODE=http
-export USE_FIXED_HTTP=true  # Important: Use fixed implementation
 export AUTH_TOKEN=$(openssl rand -base64 32)
 export PORT=3000
 
@@ -144,7 +142,6 @@ Skip HTTP entirely and use stdio mode directly:
 | Variable | Description | Example |
 |----------|-------------|------|
 | `MCP_MODE` | Must be set to `http` | `http` |
-| `USE_FIXED_HTTP` | **Important**: Set to `true` for stable implementation | `true` |
 | `AUTH_TOKEN` or `AUTH_TOKEN_FILE` | Authentication method | See security section |
 
 ### Optional Settings
@@ -417,7 +414,6 @@ services:
     environment:
       # Core configuration
       MCP_MODE: http
-      USE_FIXED_HTTP: true
       NODE_ENV: production
       
       # Security - Using file-based secret
@@ -500,7 +496,6 @@ WorkingDirectory=/opt/n8n-mcp
 # Use file-based secret
 Environment="AUTH_TOKEN_FILE=/etc/n8n-mcp/auth_token"
 Environment="MCP_MODE=http"
-Environment="USE_FIXED_HTTP=true"
 Environment="NODE_ENV=production"
 Environment="TRUST_PROXY=1"
 Environment="BASE_URL=https://n8n-mcp.example.com"
@@ -772,8 +767,8 @@ sudo ufw status  # Linux
 ```
 
 **"Stream is not readable":**
-- Ensure `USE_FIXED_HTTP=true` is set
-- Fixed in v2.3.2+
+- This issue was fixed in v2.3.2+ with the SingleSessionHTTPServer
+- No additional configuration needed
 
 **Bridge script not working:**
 ```bash
diff --git a/docs/INSTALLATION.md b/docs/INSTALLATION.md
index 3dd29ca..5f432fc 100644
--- a/docs/INSTALLATION.md
+++ b/docs/INSTALLATION.md
@@ -18,7 +18,6 @@ The fastest way to get n8n-MCP running:
 # Using Docker (recommended)
 cat > .env << EOF
 AUTH_TOKEN=$(openssl rand -base64 32)
-USE_FIXED_HTTP=true
 EOF
 docker compose up -d
 ```
@@ -49,7 +48,6 @@ docker compose up -d
        
        environment:
          MCP_MODE: ${MCP_MODE:-http}
-         USE_FIXED_HTTP: ${USE_FIXED_HTTP:-true}
          AUTH_TOKEN: ${AUTH_TOKEN:?AUTH_TOKEN is required}
          NODE_ENV: ${NODE_ENV:-production}
          LOG_LEVEL: ${LOG_LEVEL:-info}
diff --git a/docs/RAILWAY_DEPLOYMENT.md b/docs/RAILWAY_DEPLOYMENT.md
index 2c807cc..28a9ab2 100644
--- a/docs/RAILWAY_DEPLOYMENT.md
+++ b/docs/RAILWAY_DEPLOYMENT.md
@@ -98,7 +98,6 @@ These are automatically set by the Railway template:
 |----------|--------------|-------------|
 | `AUTH_TOKEN` | `REPLACE_THIS...` | **⚠️ CHANGE IMMEDIATELY** |
 | `MCP_MODE` | `http` | Required for cloud deployment |
-| `USE_FIXED_HTTP` | `true` | Stable HTTP implementation |
 | `NODE_ENV` | `production` | Production optimizations |
 | `LOG_LEVEL` | `info` | Balanced logging |
 | `TRUST_PROXY` | `1` | Railway runs behind proxy |
diff --git a/docs/README.md b/docs/README.md
index 0e9873f..34dbc4c 100644
--- a/docs/README.md
+++ b/docs/README.md
@@ -40,7 +40,6 @@ Key configuration options:
 | Variable | Description | Default |
 |----------|-------------|---------|
 | `MCP_MODE` | Server mode: `stdio` or `http` | `stdio` |
-| `USE_FIXED_HTTP` | Use fixed HTTP implementation (v2.3.2+) | `true` |
 | `AUTH_TOKEN` | Authentication token for HTTP mode | Required |
 | `PORT` | HTTP server port | `3000` |
 | `LOG_LEVEL` | Logging verbosity | `info` |
diff --git a/package.json b/package.json
index 4324970..abd1a58 100644
--- a/package.json
+++ b/package.json
@@ -22,9 +22,9 @@
     "test-nodes": "node dist/scripts/test-nodes.js",
     "start": "node dist/mcp/index.js",
     "start:http": "MCP_MODE=http node dist/mcp/index.js",
-    "start:http:fixed": "MCP_MODE=http USE_FIXED_HTTP=true node dist/mcp/index.js",
+    "start:http:fixed:deprecated": "echo 'DEPRECATED: USE_FIXED_HTTP is deprecated. Use npm run start:http instead.' && MCP_MODE=http USE_FIXED_HTTP=true node dist/mcp/index.js",
     "start:n8n": "N8N_MODE=true MCP_MODE=http node dist/mcp/index.js",
-    "http": "npm run build && npm run start:http:fixed",
+    "http": "npm run build && npm run start:http",
     "dev": "npm run build && npm run rebuild && npm run validate",
     "dev:http": "MCP_MODE=http nodemon --watch src --ext ts --exec 'npm run build && npm run start:http'",
     "test:single-session": "./scripts/test-single-session.sh",
diff --git a/scripts/test-url-configuration.ts b/scripts/test-url-configuration.ts
index c0179e8..802fb45 100755
--- a/scripts/test-url-configuration.ts
+++ b/scripts/test-url-configuration.ts
@@ -71,10 +71,12 @@ const testCases: TestCase[] = [
     }
   },
   {
-    name: 'Fixed HTTP implementation',
+    // DEPRECATED: This test case tests the deprecated fixed HTTP implementation
+    // See: https://github.com/czlonkowski/n8n-mcp/issues/524
+    name: 'Fixed HTTP implementation (DEPRECATED)',
     env: {
       MCP_MODE: 'http',
-      USE_FIXED_HTTP: 'true',
+      USE_FIXED_HTTP: 'true',  // DEPRECATED: Will be removed in future version
       AUTH_TOKEN: 'test-token-for-testing-only',
       PORT: '3005',
       BASE_URL: 'https://fixed.example.com'
diff --git a/src/http-server.ts b/src/http-server.ts
index b43f5fa..0fe4106 100644
--- a/src/http-server.ts
+++ b/src/http-server.ts
@@ -1,7 +1,14 @@
 #!/usr/bin/env node
 /**
- * Fixed HTTP server for n8n-MCP that properly handles StreamableHTTPServerTransport initialization
- * This implementation ensures the transport is properly initialized before handling requests
+ * @deprecated This fixed HTTP server is deprecated as of v2.31.7.
+ * Use SingleSessionHTTPServer from http-server-single-session.ts instead.
+ *
+ * This implementation does not support SSE streaming required by clients like OpenAI Codex.
+ * See: https://github.com/czlonkowski/n8n-mcp/issues/524
+ *
+ * Original purpose: Fixed HTTP server for n8n-MCP that properly handles
+ * StreamableHTTPServerTransport initialization by bypassing it entirely.
+ * This implementation ensures the transport is properly initialized before handling requests.
  */
 import express from 'express';
 import { Server } from '@modelcontextprotocol/sdk/server/index.js';
@@ -125,7 +132,18 @@ async function shutdown() {
   }
 }
 
+/**
+ * @deprecated Use SingleSessionHTTPServer from http-server-single-session.ts instead.
+ * This function does not support SSE streaming required by clients like OpenAI Codex.
+ */
 export async function startFixedHTTPServer() {
+  // Log deprecation warning
+  logger.warn(
+    'DEPRECATION: startFixedHTTPServer() is deprecated as of v2.31.7. ' +
+    'Use SingleSessionHTTPServer which supports SSE streaming. ' +
+    'See: https://github.com/czlonkowski/n8n-mcp/issues/524'
+  );
+
   validateEnvironment();
   
   const app = express();
diff --git a/src/mcp/index.ts b/src/mcp/index.ts
index 75af544..d846a13 100644
--- a/src/mcp/index.ts
+++ b/src/mcp/index.ts
@@ -124,9 +124,23 @@ Learn more: https://github.com/czlonkowski/n8n-mcp/blob/main/PRIVACY.md
     checkpoints.push(STARTUP_CHECKPOINTS.MCP_HANDSHAKE_STARTING);
     
     if (mode === 'http') {
-      // Check if we should use the fixed implementation
+      // Check if we should use the fixed implementation (DEPRECATED)
       if (process.env.USE_FIXED_HTTP === 'true') {
-        // Use the fixed HTTP implementation that bypasses StreamableHTTPServerTransport issues
+        // DEPRECATION WARNING: Fixed HTTP implementation is deprecated
+        // It does not support SSE streaming required by clients like OpenAI Codex
+        logger.warn(
+          'DEPRECATION WARNING: USE_FIXED_HTTP=true is deprecated as of v2.31.7. ' +
+          'The fixed HTTP implementation does not support SSE streaming required by clients like OpenAI Codex. ' +
+          'Please unset USE_FIXED_HTTP to use the modern SingleSessionHTTPServer which supports both JSON-RPC and SSE. ' +
+          'This option will be removed in a future version. See: https://github.com/czlonkowski/n8n-mcp/issues/524'
+        );
+        console.warn('\n⚠️  DEPRECATION WARNING ⚠️');
+        console.warn('USE_FIXED_HTTP=true is deprecated as of v2.31.7.');
+        console.warn('The fixed HTTP implementation does not support SSE streaming.');
+        console.warn('Please unset USE_FIXED_HTTP to use SingleSessionHTTPServer.');
+        console.warn('See: https://github.com/czlonkowski/n8n-mcp/issues/524\n');
+
+        // Use the deprecated fixed HTTP implementation
         const { startFixedHTTPServer } = await import('../http-server');
         await startFixedHTTPServer();
       } else {