diff --git a/src/inspect_ai/model/_openai.py b/src/inspect_ai/model/_openai.py
index b2459c530..0084d6196 100644
--- a/src/inspect_ai/model/_openai.py
+++ b/src/inspect_ai/model/_openai.py
@@ -38,6 +38,7 @@
 from inspect_ai._util.url import is_http_url
 from inspect_ai.model._call_tools import parse_tool_call
 from inspect_ai.model._model_output import ChatCompletionChoice, Logprobs
+from inspect_ai.model._reasoning import parse_content_with_reasoning
 from inspect_ai.tool import ToolCall, ToolChoice, ToolFunction, ToolInfo
 
 from ._chat_message import (
@@ -154,14 +155,14 @@ async def openai_chat_message(
         if message.tool_calls:
             return ChatCompletionAssistantMessageParam(
                 role=message.role,
-                content=message.text,
+                content=openai_assistant_content(message),
                 tool_calls=[
                     openai_chat_tool_call_param(call) for call in message.tool_calls
                 ],
             )
         else:
             return ChatCompletionAssistantMessageParam(
-                role=message.role, content=message.text
+                role=message.role, content=openai_assistant_content(message)
             )
     elif message.role == "tool":
         return ChatCompletionToolMessageParam(
@@ -181,16 +182,29 @@ async def openai_chat_messages(
     return [await openai_chat_message(message, model) for message in messages]
 
 
+def openai_assistant_content(message: ChatMessageAssistant) -> str:
+    if isinstance(message.content, str):
+        content = message.content
+    else:
+        content = ""
+        for c in message.content:
+            if c.type == "reasoning":
+                attribs = ""
+                if c.signature is not None:
+                    attribs = f'{attribs} signature="{c.signature}"'
+                if c.redacted:
+                    attribs = f'{attribs} redacted="true"'
+                content = f"{content}\n<think{attribs}>\n{c.reasoning}\n</think>\n"
+            elif c.type == "text":
+                content = f"{content}\n{c.text}"
+    return content
+
+
 def openai_chat_choices(choices: list[ChatCompletionChoice]) -> list[Choice]:
     oai_choices: list[Choice] = []
 
     for index, choice in enumerate(choices):
-        if isinstance(choice.message.content, str):
-            content = choice.message.content
-        else:
-            content = "\n".join(
-                [c.text for c in choice.message.content if c.type == "text"]
-            )
+        content = openai_assistant_content(choice.message)
         if choice.message.tool_calls:
             tool_calls = [openai_chat_tool_call(tc) for tc in choice.message.tool_calls]
         else:
@@ -280,35 +294,47 @@ def chat_messages_from_openai(
     chat_messages: list[ChatMessage] = []
 
     for message in messages:
+        content: str | list[Content] = []
         if message["role"] == "system" or message["role"] == "developer":
             sys_content = message["content"]
             if isinstance(sys_content, str):
                 chat_messages.append(ChatMessageSystem(content=sys_content))
             else:
-                chat_messages.append(
-                    ChatMessageSystem(
-                        content=[content_from_openai(c) for c in sys_content]
-                    )
-                )
+                content = []
+                for sc in sys_content:
+                    content.extend(content_from_openai(sc))
+                chat_messages.append(ChatMessageSystem(content=content))
         elif message["role"] == "user":
             user_content = message["content"]
             if isinstance(user_content, str):
                 chat_messages.append(ChatMessageUser(content=user_content))
             else:
-                chat_messages.append(
-                    ChatMessageUser(
-                        content=[content_from_openai(c) for c in user_content]
-                    )
-                )
+                content = []
+                for uc in user_content:
+                    content.extend(content_from_openai(uc))
+                chat_messages.append(ChatMessageUser(content=content))
         elif message["role"] == "assistant":
             # resolve content
             asst_content = message.get("content", None)
             if isinstance(asst_content, str):
-                content: str | list[Content] = asst_content
+                result = parse_content_with_reasoning(asst_content)
+                if result is not None:
+                    content = [
+                        ContentReasoning(
+                            reasoning=result.reasoning,
+                            signature=result.signature,
+                            redacted=result.redacted,
+                        ),
+                        ContentText(text=result.content),
+                    ]
+                else:
+                    content = asst_content
             elif asst_content is None:
                 content = message.get("refusal", None) or ""
             else:
-                content = [content_from_openai(c) for c in asst_content]
+                content = []
+                for ac in asst_content:
+                    content.extend(content_from_openai(ac, parse_reasoning=True))
 
             # resolve reasoning (OpenAI doesn't suport this however OpenAI-compatible
             # interfaces e.g. DeepSeek do include this field so we pluck it out)
@@ -324,9 +350,9 @@ def chat_messages_from_openai(
             # return message
             if "tool_calls" in message:
                 tool_calls: list[ToolCall] = []
-                for tc in message["tool_calls"]:
-                    tool_calls.append(tool_call_from_openai(tc))
-                    tool_names[tc["id"]] = tc["function"]["name"]
+                for call in message["tool_calls"]:
+                    tool_calls.append(tool_call_from_openai(call))
+                    tool_names[call["id"]] = call["function"]["name"]
 
             else:
                 tool_calls = []
@@ -342,7 +368,9 @@ def chat_messages_from_openai(
             if isinstance(tool_content, str):
                 content = tool_content
             else:
-                content = [content_from_openai(c) for c in tool_content]
+                content = []
+                for tc in tool_content:
+                    content.extend(content_from_openai(tc))
             chat_messages.append(
                 ChatMessageTool(
                     content=content,
@@ -366,20 +394,40 @@ def tool_call_from_openai(tool_call: ChatCompletionMessageToolCallParam) -> Tool
 
 def content_from_openai(
     content: ChatCompletionContentPartParam | ChatCompletionContentPartRefusalParam,
-) -> Content:
+    parse_reasoning: bool = False,
+) -> list[Content]:
     if content["type"] == "text":
-        return ContentText(text=content["text"])
+        text = content["text"]
+        if parse_reasoning:
+            result = parse_content_with_reasoning(text)
+            if result:
+                return [
+                    ContentReasoning(
+                        reasoning=result.reasoning,
+                        signature=result.signature,
+                        redacted=result.redacted,
+                    ),
+                    ContentText(text=result.content),
+                ]
+            else:
+                return [ContentText(text=text)]
+        else:
+            return [ContentText(text=text)]
     elif content["type"] == "image_url":
-        return ContentImage(
-            image=content["image_url"]["url"], detail=content["image_url"]["detail"]
-        )
+        return [
+            ContentImage(
+                image=content["image_url"]["url"], detail=content["image_url"]["detail"]
+            )
+        ]
     elif content["type"] == "input_audio":
-        return ContentAudio(
-            audio=content["input_audio"]["data"],
-            format=content["input_audio"]["format"],
-        )
+        return [
+            ContentAudio(
+                audio=content["input_audio"]["data"],
+                format=content["input_audio"]["format"],
+            )
+        ]
     elif content["type"] == "refusal":
-        return ContentText(text=content["refusal"])
+        return [ContentText(text=content["refusal"])]
 
 
 def chat_message_assistant_from_openai(
diff --git a/src/inspect_ai/model/_reasoning.py b/src/inspect_ai/model/_reasoning.py
index 7e9a5befa..d341acfb5 100644
--- a/src/inspect_ai/model/_reasoning.py
+++ b/src/inspect_ai/model/_reasoning.py
@@ -5,13 +5,26 @@
 class ContentWithReasoning(NamedTuple):
     content: str
     reasoning: str
+    signature: str | None = None
+    redacted: bool = False
 
 
 def parse_content_with_reasoning(content: str) -> ContentWithReasoning | None:
-    match = re.match(r"\s*<think>(.*?)</think>(.*)", content, re.DOTALL)
+    # Match <think> tag with optional attributes
+    pattern = r'\s*<think(?:\s+signature="([^"]*)")?(?:\s+redacted="(true)")?\s*>(.*?)</think>(.*)'
+    match = re.match(pattern, content, re.DOTALL)
+
     if match:
+        signature = match.group(1)  # This will be None if not present
+        redacted_value = match.group(2)  # This will be "true" or None
+        reasoning = match.group(3).strip()
+        content_text = match.group(4).strip()
+
         return ContentWithReasoning(
-            content=match.group(2).strip(), reasoning=match.group(1).strip()
+            content=content_text,
+            reasoning=reasoning,
+            signature=signature,
+            redacted=redacted_value == "true",
         )
     else:
         return None
diff --git a/tests/model/test_reasoning_parse.py b/tests/model/test_reasoning_parse.py
index 5818da11a..3af46c4c8 100644
--- a/tests/model/test_reasoning_parse.py
+++ b/tests/model/test_reasoning_parse.py
@@ -6,6 +6,8 @@ def test_reasoning_parse_basic():
     assert result is not None
     assert result.reasoning == "Simple reasoning"
     assert result.content == "Normal text"
+    assert result.signature is None
+    assert result.redacted is False
 
 
 def test_reasoning_parse_with_leading_whitespace():
@@ -15,6 +17,8 @@ def test_reasoning_parse_with_leading_whitespace():
     assert result is not None
     assert result.reasoning == "Indented reasoning"
     assert result.content == "Text"
+    assert result.signature is None
+    assert result.redacted is False
 
 
 def test_reasoning_parse_with_trailing_whitespace():
@@ -22,6 +26,8 @@ def test_reasoning_parse_with_trailing_whitespace():
     assert result is not None
     assert result.reasoning == "Reasoning"
     assert result.content == "Text"
+    assert result.signature is None
+    assert result.redacted is False
 
 
 def test_reasoning_parse_with_newlines_in_reasoning():
@@ -29,6 +35,8 @@ def test_reasoning_parse_with_newlines_in_reasoning():
     assert result is not None
     assert result.reasoning == "Multi\nline\nreasoning"
     assert result.content == "Text"
+    assert result.signature is None
+    assert result.redacted is False
 
 
 def test_reasoning_parse_empty():
@@ -36,6 +44,8 @@ def test_reasoning_parse_empty():
     assert result is not None
     assert result.reasoning == ""
     assert result.content == "Text"
+    assert result.signature is None
+    assert result.redacted is False
 
 
 def test_reasoning_parse_empty_content():
@@ -43,6 +53,8 @@ def test_reasoning_parse_empty_content():
     assert result is not None
     assert result.reasoning == "Just reasoning"
     assert result.content == ""
+    assert result.signature is None
+    assert result.redacted is False
 
 
 def test_reasoning_parse_whitespace_everywhere():
@@ -57,6 +69,8 @@ def test_reasoning_parse_whitespace_everywhere():
     assert result is not None
     assert result.reasoning == "Messy\n            reasoning"
     assert result.content == "Messy\n            text"
+    assert result.signature is None
+    assert result.redacted is False
 
 
 def test_reasoning_parse_no_think_tag():
@@ -67,3 +81,68 @@ def test_reasoning_parse_no_think_tag():
 def test_reasoning_parse_unclosed_tag():
     result = parse_content_with_reasoning("<think>Unclosed reasoning")
     assert result is None
+
+
+# New tests for signature attribute
+def test_reasoning_parse_with_signature():
+    result = parse_content_with_reasoning(
+        '<think signature="45ef5ab">Reasoning with signature</think>Content'
+    )
+    assert result is not None
+    assert result.reasoning == "Reasoning with signature"
+    assert result.content == "Content"
+    assert result.signature == "45ef5ab"
+    assert result.redacted is False
+
+
+# New tests for redacted attribute
+def test_reasoning_parse_with_redacted():
+    result = parse_content_with_reasoning(
+        '<think redacted="true">Redacted reasoning</think>Content'
+    )
+    assert result is not None
+    assert result.reasoning == "Redacted reasoning"
+    assert result.content == "Content"
+    assert result.signature is None
+    assert result.redacted is True
+
+
+# New tests for both attributes
+def test_reasoning_parse_with_signature_and_redacted():
+    result = parse_content_with_reasoning(
+        '<think signature="45ef5ab" redacted="true">Both attributes</think>Content'
+    )
+    assert result is not None
+    assert result.reasoning == "Both attributes"
+    assert result.content == "Content"
+    assert result.signature == "45ef5ab"
+    assert result.redacted is True
+
+
+# Test with whitespace in attributes
+def test_reasoning_parse_with_whitespace_in_attributes():
+    result = parse_content_with_reasoning(
+        '<think  signature="45ef5ab"  redacted="true" >Whitespace in attributes</think>Content'
+    )
+    assert result is not None
+    assert result.reasoning == "Whitespace in attributes"
+    assert result.content == "Content"
+    assert result.signature == "45ef5ab"
+    assert result.redacted is True
+
+
+# Test with attributes and multiline content
+def test_reasoning_parse_with_attributes_and_multiline():
+    result = parse_content_with_reasoning("""
+        <think signature="45ef5ab" redacted="true">
+            Complex
+            reasoning
+        </think>
+            Content
+            here
+    """)
+    assert result is not None
+    assert result.reasoning == "Complex\n            reasoning"
+    assert result.content == "Content\n            here"
+    assert result.signature == "45ef5ab"
+    assert result.redacted is True