diff --git a/run_agent.py b/run_agent.py
index 0051fce63f..33635ef2fe 100644
--- a/run_agent.py
+++ b/run_agent.py
@@ -2172,17 +2172,49 @@ class AIAgent:
return bool(cleaned.strip())
def _strip_think_blocks(self, content: str) -> str:
- """Remove reasoning/thinking blocks from content, returning only visible text."""
+ """Remove reasoning/thinking blocks from content, returning only visible text.
+
+ Handles four cases:
+ 1. Closed tag pairs (``…``) — the common path when
+ the provider emits complete reasoning blocks.
+ 2. Unterminated open tag at a block boundary (start of text or
+ after a newline) — e.g. MiniMax M2.7 / NIM endpoints where the
+ closing tag is dropped. Everything from the open tag to end
+ of string is stripped. The block-boundary check mirrors
+ ``gateway/stream_consumer.py``'s filter so models that mention
+ ```` in prose aren't over-stripped.
+ 3. Stray orphan open/close tags that slip through.
+ 4. Tag variants: ````, ````, ````,
+ ````, ```` (Gemma 4), all
+ case-insensitive.
+ """
if not content:
return ""
- # Strip all reasoning tag variants: , , ,
- # , , (Gemma 4)
- content = re.sub(r'.*?', '', content, flags=re.DOTALL)
+ # 1. Closed tag pairs — case-insensitive for all variants so
+ # mixed-case tags (, ) don't slip through to
+ # the unterminated-tag pass and take trailing content with them.
+ content = re.sub(r'.*?', '', content, flags=re.DOTALL | re.IGNORECASE)
content = re.sub(r'.*?', '', content, flags=re.DOTALL | re.IGNORECASE)
- content = re.sub(r'.*?', '', content, flags=re.DOTALL)
- content = re.sub(r'.*?', '', content, flags=re.DOTALL)
+ content = re.sub(r'.*?', '', content, flags=re.DOTALL | re.IGNORECASE)
+ content = re.sub(r'.*?', '', content, flags=re.DOTALL | re.IGNORECASE)
content = re.sub(r'.*?', '', content, flags=re.DOTALL | re.IGNORECASE)
- content = re.sub(r'\s*', '', content, flags=re.IGNORECASE)
+ # 2. Unterminated reasoning block — open tag at a block boundary
+ # (start of text, or after a newline) with no matching close.
+ # Strip from the tag to end of string. Fixes #8878 / #9568
+ # (MiniMax M2.7 leaking raw reasoning into assistant content).
+ content = re.sub(
+ r'(?:^|\n)[ \t]*<(?:think|thinking|reasoning|thought|REASONING_SCRATCHPAD)\b[^>]*>.*$',
+ '',
+ content,
+ flags=re.DOTALL | re.IGNORECASE,
+ )
+ # 3. Stray orphan open/close tags that slipped through.
+ content = re.sub(
+ r'\s*',
+ '',
+ content,
+ flags=re.IGNORECASE,
+ )
return content
@staticmethod
diff --git a/tests/run_agent/test_run_agent.py b/tests/run_agent/test_run_agent.py
index 86f95580f0..bde5ed5aae 100644
--- a/tests/run_agent/test_run_agent.py
+++ b/tests/run_agent/test_run_agent.py
@@ -317,6 +317,60 @@ class TestStripThinkBlocks:
result = agent._strip_think_blocks("orphaned reasoning without close")
assert "" not in result
+ # ─── Unterminated-block coverage (#8878, #9568, #10408) ──────────────
+ # Reasoning models served via NIM / MiniMax M2.7 frequently drop the
+ # closing tag, leaking raw reasoning into assistant content. The open
+ # tag appears at a block boundary (start of text or after a newline);
+ # everything from that tag to end-of-string is stripped.
+
+ def test_unterminated_think_block_content_stripped(self, agent):
+ """Content after unterminated is fully stripped."""
+ result = agent._strip_think_blocks("orphaned reasoning without close")
+ assert "orphaned reasoning" not in result
+ assert result.strip() == ""
+
+ def test_unterminated_thought_block_content_stripped(self, agent):
+ """Gemma-style with no close is fully stripped."""
+ result = agent._strip_think_blocks("orphaned reasoning without close")
+ assert "orphaned reasoning" not in result
+ assert result.strip() == ""
+
+ def test_unterminated_multiline_block_stripped(self, agent):
+ """Multi-line unterminated blocks are stripped in full."""
+ result = agent._strip_think_blocks(
+ "\nmulti\nline\nreasoning\nthat never closes"
+ )
+ assert "multi" not in result
+ assert "never closes" not in result
+
+ def test_unterminated_block_after_answer_preserves_prefix(self, agent):
+ """Visible answer before a line-starting unterminated tag is kept."""
+ result = agent._strip_think_blocks(
+ "Answer is 42.\nactually let me reconsider"
+ )
+ assert "Answer is 42." in result
+ assert "reconsider" not in result
+
+ def test_inline_think_mention_in_prose_not_over_stripped(self, agent):
+ """Mid-line `` mentioned in prose must not swallow the rest
+ of the content (the block-boundary check prevents this)."""
+ text = "Use the tag like this in your prose."
+ result = agent._strip_think_blocks(text)
+ # Block-boundary check prevents unterminated-strip from firing
+ assert "prose" in result
+ assert "Use the" in result
+
+ def test_mixed_case_closed_pair_stripped(self, agent):
+ """Mixed-case variants …, … are
+ handled by case-insensitive closed-pair regex, so the trailing
+ content is preserved."""
+ result = agent._strip_think_blocks("upperfinal")
+ assert "upper" not in result
+ assert "final" in result
+ result = agent._strip_think_blocks("mixedfinal")
+ assert "mixed" not in result
+ assert "final" in result
+
class TestExtractReasoning:
def test_reasoning_field(self, agent):