Looks like PSR-7 will be Psr\Http\Message"

Author: Phil Sturgeon

composer.json

@@ -11,7 +11,7 @@
     ],
     "autoload": {
         "psr-4": {
-            "Psr\\HttpMessage\\": "src"
+            "Psr\\Http\\Message\\": "src"
         }
     },
     "extra": {

src/MessageInterface.php

@@ -1,6 +1,6 @@
 <?php
 
-namespace Psr\HttpMessage;
+namespace Psr\Http\Message;
 
 /**
  * HTTP messages consist of requests from a client to a server and responses

src/RequestInterface.php

@@ -1,6 +1,6 @@
 <?php
 
-namespace Psr\HttpMessage;
+namespace Psr\Http\Message;
 
 /**
  * A HTTP request message.

src/ResponseInterface.php

@@ -1,6 +1,6 @@
 <?php
 
-namespace Psr\HttpMessage;
+namespace Psr\Http\Message;
 
 /**
  * A HTTP response message.

src/StreamInterface.php

@@ -1,6 +1,6 @@
 <?php
 
-namespace Psr\HttpMessage;
+namespace Psr\Http\Message;
 
 /**
  * Describes a stream instance.