diff --git a/agent_sdks/python/a2ui_agent/CHANGELOG.md b/agent_sdks/python/a2ui_agent/CHANGELOG.md
index 3f227bdc9f..67814d2cd6 100644
--- a/agent_sdks/python/a2ui_agent/CHANGELOG.md
+++ b/agent_sdks/python/a2ui_agent/CHANGELOG.md
@@ -1,5 +1,8 @@
 ## Unreleased
 
+- Invoke ANTLR from the grammar's directory when regenerating the Express parser, so generated file headers no longer embed the absolute path of the machine that built them.
+- Stop rewriting the non-package fallback import in the generated Express visitor to a relative import, which pointed at a module name the rename step had already replaced. A from-source build now leaves the working tree clean.
+
 ## 0.5.0
 
 - Rename inference format `Transport` / `transport` terminology to `Direct JSON` / `direct_json` (`DirectJsonFormat`, `DirectJsonParser`, `DirectJsonStreamParser`). Deprecate `a2ui.inference_formats.transport` module alias.
diff --git a/agent_sdks/python/a2ui_agent/README.md b/agent_sdks/python/a2ui_agent/README.md
index e18deb7db0..708bf3bf1a 100644
--- a/agent_sdks/python/a2ui_agent/README.md
+++ b/agent_sdks/python/a2ui_agent/README.md
@@ -59,6 +59,10 @@ protocol.
 
 ## Building the SDK
 
+Building from source regenerates the Express parser from
+`specification/inference_formats/express/Express.g4`. That step runs ANTLR, which
+requires a Java runtime (JRE 11 or newer) on the `PATH`.
+
 To build the SDK, run the following command from the `agent_sdks/python/a2ui_agent`
 directory:
 
diff --git a/agent_sdks/python/a2ui_agent/pack_specs_hook.py b/agent_sdks/python/a2ui_agent/pack_specs_hook.py
index 57673dfbc9..09730e0c7c 100644
--- a/agent_sdks/python/a2ui_agent/pack_specs_hook.py
+++ b/agent_sdks/python/a2ui_agent/pack_specs_hook.py
@@ -132,15 +132,15 @@ def initialize(self, version, build_data):
                 "-visitor",
                 "-no-listener",
                 "-o",
-                "generated",
-                g4_path,
+                os.path.abspath(generated_dir),
+                os.path.basename(g4_path),
             ]
             env = os.environ.copy()
             env["ANTLR4_TOOLS_ANTLR_VERSION"] = "4.13.2"
 
             res = subprocess.run(
                 cmd,
-                cwd=express_dir,
+                cwd=os.path.dirname(g4_path),
                 env=env,
                 capture_output=True,
                 text=True,
@@ -190,7 +190,7 @@ def initialize(self, version, build_data):
                     "from .ExpressParser import", "from .express_parser import"
                 )
                 content = content.replace(
-                    "from ExpressParser import", "from .express_parser import"
+                    "from ExpressParser import", "from express_parser import"
                 )
                 with open(visitor_path, "w", encoding="utf-8") as f:
                     f.write(content)
diff --git a/agent_sdks/python/a2ui_agent/src/a2ui/inference_formats/experimental/express/generated/express_lexer.py b/agent_sdks/python/a2ui_agent/src/a2ui/inference_formats/experimental/express/generated/express_lexer.py
index 2696a12b7e..f35fe0070b 100644
--- a/agent_sdks/python/a2ui_agent/src/a2ui/inference_formats/experimental/express/generated/express_lexer.py
+++ b/agent_sdks/python/a2ui_agent/src/a2ui/inference_formats/experimental/express/generated/express_lexer.py
@@ -1,4 +1,4 @@
-# Generated from /usr/local/google/home/gspencer/code/a2ui/kotlin_express/specification/inference_formats/express/Express.g4 by ANTLR 4.13.2
+# Generated from Express.g4 by ANTLR 4.13.2
 from antlr4 import *
 from io import StringIO
 import sys
diff --git a/agent_sdks/python/a2ui_agent/src/a2ui/inference_formats/experimental/express/generated/express_parser.py b/agent_sdks/python/a2ui_agent/src/a2ui/inference_formats/experimental/express/generated/express_parser.py
index cb929c782c..827a9d28b7 100644
--- a/agent_sdks/python/a2ui_agent/src/a2ui/inference_formats/experimental/express/generated/express_parser.py
+++ b/agent_sdks/python/a2ui_agent/src/a2ui/inference_formats/experimental/express/generated/express_parser.py
@@ -1,4 +1,4 @@
-# Generated from /usr/local/google/home/gspencer/code/a2ui/kotlin_express/specification/inference_formats/express/Express.g4 by ANTLR 4.13.2
+# Generated from Express.g4 by ANTLR 4.13.2
 # encoding: utf-8
 from antlr4 import *
 from io import StringIO
diff --git a/agent_sdks/python/a2ui_agent/src/a2ui/inference_formats/experimental/express/generated/express_visitor.py b/agent_sdks/python/a2ui_agent/src/a2ui/inference_formats/experimental/express/generated/express_visitor.py
index 9bd827cec7..6f29f2da66 100644
--- a/agent_sdks/python/a2ui_agent/src/a2ui/inference_formats/experimental/express/generated/express_visitor.py
+++ b/agent_sdks/python/a2ui_agent/src/a2ui/inference_formats/experimental/express/generated/express_visitor.py
@@ -1,11 +1,10 @@
-# Generated from /usr/local/google/home/gspencer/code/a2ui/kotlin_express/specification/inference_formats/express/Express.g4 by ANTLR 4.13.2
+# Generated from Express.g4 by ANTLR 4.13.2
 from antlr4 import *
 if "." in __name__:
     from .express_parser import ExpressParser
 else:
     from express_parser import ExpressParser
 
-
 # This class defines a complete generic visitor for a parse tree produced by ExpressParser.
 
 class ExpressVisitor(ParseTreeVisitor):