diff --git a/python/Makefile b/python/Makefile
index 45d9595a..cf6c567c 100644
--- a/python/Makefile
+++ b/python/Makefile
@@ -14,6 +14,7 @@ generate: require install-deps
 		--input $(HERE)../jsonschema/Envelope.json \
 		--output $(HERE)src/_messages.py \
 		--use-generic-container-types \
+		--allow-extra-fields \
 		--allow-population-by-field-name \
 		--snake-case-field \
 		--input-file-type=jsonschema \
diff --git a/python/src/_messages.py b/python/src/_messages.py
index 97dc5918..e37c6d53 100644
--- a/python/src/_messages.py
+++ b/python/src/_messages.py
@@ -21,7 +21,7 @@ class MediaType(Enum):
 
 class Source(BaseModel):
     model_config = ConfigDict(
-        extra="forbid",
+        extra="allow",
         populate_by_name=True,
     )
     uri: str = Field(
@@ -38,7 +38,7 @@ class Source(BaseModel):
 
 class Location(BaseModel):
     model_config = ConfigDict(
-        extra="forbid",
+        extra="allow",
         populate_by_name=True,
     )
     line: int
@@ -47,7 +47,7 @@ class Location(BaseModel):
 
 class Comment(BaseModel):
     model_config = ConfigDict(
-        extra="forbid",
+        extra="allow",
         populate_by_name=True,
     )
     location: Location = Field(..., description="The location of the comment")
@@ -56,7 +56,7 @@ class Comment(BaseModel):
 
 class DocString(BaseModel):
     model_config = ConfigDict(
-        extra="forbid",
+        extra="allow",
         populate_by_name=True,
     )
     location: Location
@@ -75,7 +75,7 @@ class KeywordType(Enum):
 
 class TableCell(BaseModel):
     model_config = ConfigDict(
-        extra="forbid",
+        extra="allow",
         populate_by_name=True,
     )
     location: Location = Field(..., description="The location of the cell")
@@ -84,7 +84,7 @@ class TableCell(BaseModel):
 
 class TableRow(BaseModel):
     model_config = ConfigDict(
-        extra="forbid",
+        extra="allow",
         populate_by_name=True,
     )
     location: Location = Field(..., description="The location of the first cell in the row")
@@ -94,7 +94,7 @@ class TableRow(BaseModel):
 
 class Tag(BaseModel):
     model_config = ConfigDict(
-        extra="forbid",
+        extra="allow",
         populate_by_name=True,
     )
     location: Location = Field(..., description="Location of the tag")
@@ -104,7 +104,7 @@ class Tag(BaseModel):
 
 class JavaMethod(BaseModel):
     model_config = ConfigDict(
-        extra="forbid",
+        extra="allow",
         populate_by_name=True,
     )
     class_name: str = Field(..., alias="className")
@@ -114,7 +114,7 @@ class JavaMethod(BaseModel):
 
 class JavaStackTraceElement(BaseModel):
     model_config = ConfigDict(
-        extra="forbid",
+        extra="allow",
         populate_by_name=True,
     )
     class_name: str = Field(..., alias="className")
@@ -124,7 +124,7 @@ class JavaStackTraceElement(BaseModel):
 
 class Git(BaseModel):
     model_config = ConfigDict(
-        extra="forbid",
+        extra="allow",
         populate_by_name=True,
     )
     remote: str
@@ -135,7 +135,7 @@ class Git(BaseModel):
 
 class Product(BaseModel):
     model_config = ConfigDict(
-        extra="forbid",
+        extra="allow",
         populate_by_name=True,
     )
     name: str = Field(..., description="The product name")
@@ -144,7 +144,7 @@ class Product(BaseModel):
 
 class PickleDocString(BaseModel):
     model_config = ConfigDict(
-        extra="forbid",
+        extra="allow",
         populate_by_name=True,
     )
     media_type: str | None = Field(None, alias="mediaType")
@@ -160,7 +160,7 @@ class Type(Enum):
 
 class PickleTableCell(BaseModel):
     model_config = ConfigDict(
-        extra="forbid",
+        extra="allow",
         populate_by_name=True,
     )
     value: str
@@ -168,7 +168,7 @@ class PickleTableCell(BaseModel):
 
 class PickleTableRow(BaseModel):
     model_config = ConfigDict(
-        extra="forbid",
+        extra="allow",
         populate_by_name=True,
     )
     cells: Sequence[PickleTableCell] = Field(..., min_length=1)
@@ -176,7 +176,7 @@ class PickleTableRow(BaseModel):
 
 class PickleTag(BaseModel):
     model_config = ConfigDict(
-        extra="forbid",
+        extra="allow",
         populate_by_name=True,
     )
     name: str
@@ -190,7 +190,7 @@ class Type1(Enum):
 
 class StepDefinitionPattern(BaseModel):
     model_config = ConfigDict(
-        extra="forbid",
+        extra="allow",
         populate_by_name=True,
     )
     source: str
@@ -199,7 +199,7 @@ class StepDefinitionPattern(BaseModel):
 
 class Group(BaseModel):
     model_config = ConfigDict(
-        extra="forbid",
+        extra="allow",
         populate_by_name=True,
     )
     children: Sequence[Group]
@@ -209,7 +209,7 @@ class Group(BaseModel):
 
 class StepMatchArgument(BaseModel):
     model_config = ConfigDict(
-        extra="forbid",
+        extra="allow",
         populate_by_name=True,
     )
     group: Group = Field(
@@ -221,7 +221,7 @@ class StepMatchArgument(BaseModel):
 
 class StepMatchArgumentsList(BaseModel):
     model_config = ConfigDict(
-        extra="forbid",
+        extra="allow",
         populate_by_name=True,
     )
     step_match_arguments: Sequence[StepMatchArgument] = Field(..., alias="stepMatchArguments")
@@ -229,7 +229,7 @@ class StepMatchArgumentsList(BaseModel):
 
 class TestStep(BaseModel):
     model_config = ConfigDict(
-        extra="forbid",
+        extra="allow",
         populate_by_name=True,
     )
     hook_id: str | None = Field(None, alias="hookId", description="Pointer to the `Hook` (if derived from a Hook)")
@@ -251,7 +251,7 @@ class TestStep(BaseModel):
 
 class Timestamp(BaseModel):
     model_config = ConfigDict(
-        extra="forbid",
+        extra="allow",
         populate_by_name=True,
     )
     seconds: int = Field(
@@ -266,7 +266,7 @@ class Timestamp(BaseModel):
 
 class TestCaseStarted(BaseModel):
     model_config = ConfigDict(
-        extra="forbid",
+        extra="allow",
         populate_by_name=True,
     )
     attempt: int = Field(
@@ -288,7 +288,7 @@ class TestCaseStarted(BaseModel):
 
 class Exception(BaseModel):
     model_config = ConfigDict(
-        extra="forbid",
+        extra="allow",
         populate_by_name=True,
     )
     type: str = Field(
@@ -305,7 +305,7 @@ class Exception(BaseModel):
 
 class TestRunStarted(BaseModel):
     model_config = ConfigDict(
-        extra="forbid",
+        extra="allow",
         populate_by_name=True,
     )
     timestamp: Timestamp
@@ -323,7 +323,7 @@ class Status(Enum):
 
 class Duration(BaseModel):
     model_config = ConfigDict(
-        extra="forbid",
+        extra="allow",
         populate_by_name=True,
     )
     seconds: int
@@ -335,7 +335,7 @@ class Duration(BaseModel):
 
 class TestStepStarted(BaseModel):
     model_config = ConfigDict(
-        extra="forbid",
+        extra="allow",
         populate_by_name=True,
     )
     test_case_started_id: str = Field(..., alias="testCaseStartedId")
@@ -345,7 +345,7 @@ class TestStepStarted(BaseModel):
 
 class UndefinedParameterType(BaseModel):
     model_config = ConfigDict(
-        extra="forbid",
+        extra="allow",
         populate_by_name=True,
     )
     expression: str
@@ -354,7 +354,7 @@ class UndefinedParameterType(BaseModel):
 
 class Attachment(BaseModel):
     model_config = ConfigDict(
-        extra="forbid",
+        extra="allow",
         populate_by_name=True,
     )
     body: str = Field(
@@ -387,7 +387,7 @@ class Attachment(BaseModel):
 
 class DataTable(BaseModel):
     model_config = ConfigDict(
-        extra="forbid",
+        extra="allow",
         populate_by_name=True,
     )
     location: Location
@@ -396,7 +396,7 @@ class DataTable(BaseModel):
 
 class Examples(BaseModel):
     model_config = ConfigDict(
-        extra="forbid",
+        extra="allow",
         populate_by_name=True,
     )
     location: Location = Field(..., description="The location of the `Examples` keyword")
@@ -411,7 +411,7 @@ class Examples(BaseModel):
 
 class Step(BaseModel):
     model_config = ConfigDict(
-        extra="forbid",
+        extra="allow",
         populate_by_name=True,
     )
     location: Location = Field(..., description="The location of the steps' `keyword`")
@@ -429,7 +429,7 @@ class Step(BaseModel):
 
 class SourceReference(BaseModel):
     model_config = ConfigDict(
-        extra="forbid",
+        extra="allow",
         populate_by_name=True,
     )
     uri: str | None = None
@@ -440,7 +440,7 @@ class SourceReference(BaseModel):
 
 class Ci(BaseModel):
     model_config = ConfigDict(
-        extra="forbid",
+        extra="allow",
         populate_by_name=True,
     )
     name: str = Field(..., description='Name of the CI product, e.g. "Jenkins", "CircleCI" etc.')
@@ -455,7 +455,7 @@ class Ci(BaseModel):
 
 class ParameterType(BaseModel):
     model_config = ConfigDict(
-        extra="forbid",
+        extra="allow",
         populate_by_name=True,
     )
     name: str = Field(..., description="The name is unique, so we don't need an id.")
@@ -468,7 +468,7 @@ class ParameterType(BaseModel):
 
 class ParseError(BaseModel):
     model_config = ConfigDict(
-        extra="forbid",
+        extra="allow",
         populate_by_name=True,
     )
     source: SourceReference
@@ -477,7 +477,7 @@ class ParseError(BaseModel):
 
 class PickleTable(BaseModel):
     model_config = ConfigDict(
-        extra="forbid",
+        extra="allow",
         populate_by_name=True,
     )
     rows: Sequence[PickleTableRow]
@@ -485,7 +485,7 @@ class PickleTable(BaseModel):
 
 class StepDefinition(BaseModel):
     model_config = ConfigDict(
-        extra="forbid",
+        extra="allow",
         populate_by_name=True,
     )
     id: str
@@ -495,7 +495,7 @@ class StepDefinition(BaseModel):
 
 class TestCase(BaseModel):
     model_config = ConfigDict(
-        extra="forbid",
+        extra="allow",
         populate_by_name=True,
     )
     id: str
@@ -505,7 +505,7 @@ class TestCase(BaseModel):
 
 class TestCaseFinished(BaseModel):
     model_config = ConfigDict(
-        extra="forbid",
+        extra="allow",
         populate_by_name=True,
     )
     test_case_started_id: str = Field(..., alias="testCaseStartedId")
@@ -515,7 +515,7 @@ class TestCaseFinished(BaseModel):
 
 class TestRunFinished(BaseModel):
     model_config = ConfigDict(
-        extra="forbid",
+        extra="allow",
         populate_by_name=True,
     )
     message: str | None = Field(
@@ -535,7 +535,7 @@ class TestRunFinished(BaseModel):
 
 class TestStepResult(BaseModel):
     model_config = ConfigDict(
-        extra="forbid",
+        extra="allow",
         populate_by_name=True,
     )
     duration: Duration
@@ -549,7 +549,7 @@ class TestStepResult(BaseModel):
 
 class Background(BaseModel):
     model_config = ConfigDict(
-        extra="forbid",
+        extra="allow",
         populate_by_name=True,
     )
     location: Location = Field(..., description="The location of the `Background` keyword")
@@ -562,7 +562,7 @@ class Background(BaseModel):
 
 class Scenario(BaseModel):
     model_config = ConfigDict(
-        extra="forbid",
+        extra="allow",
         populate_by_name=True,
     )
     location: Location = Field(..., description="The location of the `Scenario` keyword")
@@ -577,7 +577,7 @@ class Scenario(BaseModel):
 
 class Hook(BaseModel):
     model_config = ConfigDict(
-        extra="forbid",
+        extra="allow",
         populate_by_name=True,
     )
     id: str
@@ -588,7 +588,7 @@ class Hook(BaseModel):
 
 class Meta(BaseModel):
     model_config = ConfigDict(
-        extra="forbid",
+        extra="allow",
         populate_by_name=True,
     )
     protocol_version: str = Field(
@@ -603,7 +603,7 @@ class Meta(BaseModel):
 
 class PickleStepArgument(BaseModel):
     model_config = ConfigDict(
-        extra="forbid",
+        extra="allow",
         populate_by_name=True,
     )
     doc_string: PickleDocString | None = Field(None, alias="docString")
@@ -612,7 +612,7 @@ class PickleStepArgument(BaseModel):
 
 class TestStepFinished(BaseModel):
     model_config = ConfigDict(
-        extra="forbid",
+        extra="allow",
         populate_by_name=True,
     )
     test_case_started_id: str = Field(..., alias="testCaseStartedId")
@@ -623,7 +623,7 @@ class TestStepFinished(BaseModel):
 
 class RuleChild(BaseModel):
     model_config = ConfigDict(
-        extra="forbid",
+        extra="allow",
         populate_by_name=True,
     )
     background: Background | None = None
@@ -632,7 +632,7 @@ class RuleChild(BaseModel):
 
 class PickleStep(BaseModel):
     model_config = ConfigDict(
-        extra="forbid",
+        extra="allow",
         populate_by_name=True,
     )
     argument: PickleStepArgument | None = None
@@ -652,7 +652,7 @@ class PickleStep(BaseModel):
 
 class Rule(BaseModel):
     model_config = ConfigDict(
-        extra="forbid",
+        extra="allow",
         populate_by_name=True,
     )
     location: Location = Field(..., description="The location of the `Rule` keyword")
@@ -666,7 +666,7 @@ class Rule(BaseModel):
 
 class Pickle(BaseModel):
     model_config = ConfigDict(
-        extra="forbid",
+        extra="allow",
         populate_by_name=True,
     )
     id: str = Field(..., description="*\n A unique id for the pickle")
@@ -688,7 +688,7 @@ class Pickle(BaseModel):
 
 class FeatureChild(BaseModel):
     model_config = ConfigDict(
-        extra="forbid",
+        extra="allow",
         populate_by_name=True,
     )
     rule: Rule | None = None
@@ -698,7 +698,7 @@ class FeatureChild(BaseModel):
 
 class Feature(BaseModel):
     model_config = ConfigDict(
-        extra="forbid",
+        extra="allow",
         populate_by_name=True,
     )
     location: Location = Field(..., description="The location of the `Feature` keyword")
@@ -717,7 +717,7 @@ class Feature(BaseModel):
 
 class GherkinDocument(BaseModel):
     model_config = ConfigDict(
-        extra="forbid",
+        extra="allow",
         populate_by_name=True,
     )
     uri: str | None = Field(
@@ -730,7 +730,7 @@ class GherkinDocument(BaseModel):
 
 class Envelope(BaseModel):
     model_config = ConfigDict(
-        extra="forbid",
+        extra="allow",
         populate_by_name=True,
     )
     attachment: Attachment | None = None