Skip to content

[Bugfix] Fix step3p5 reasoning with interleaved thinking #34211

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
chaunceyjiang merged 2 commits into from
Feb 25, 2026
Merged

[Bugfix] Fix step3p5 reasoning with interleaved thinking #34211

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
2 commits
Select commit Hold shift + click to select a range
7875fdb
fix step3p5 reasoning
mariohong128 Feb 10, 2026
ab1e739
Merge branch 'main' into fix_step3p5_reasoning
chaunceyjiang Feb 25, 2026
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
341 changes: 341 additions & 0 deletions tests/reasoning/test_step3p5_reasoning_parser.py
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1,341 @@
# SPDX-License-Identifier: Apache-2.0
# SPDX-FileCopyrightText: Copyright contributors to the vLLM project

import pytest
from transformers import AutoTokenizer

from tests.reasoning.utils import run_reasoning_extraction
from vllm.reasoning import ReasoningParser, ReasoningParserManager

parser_name = "step3p5"
start_token = "<think>"
end_token = "</think>"

REASONING_MODEL_NAME = "stepfun-ai/Step-3.5-Flash"


@pytest.fixture(scope="module")
def step3p5_tokenizer():
return AutoTokenizer.from_pretrained(REASONING_MODEL_NAME)


SIMPLE_REASONING = {
"output": "This is a reasoning section</think>This is the rest",
"reasoning_content": "This is a reasoning section",
"content": "This is the rest",
"is_reasoning_end": True,
}
# need to get into parser again to remove newline after </think>
COMPLETE_REASONING = {
"output": "This is a reasoning section</think>",
"reasoning_content": "This is a reasoning section",
"content": None,
"is_reasoning_end": False,
}
NO_CONTENT = {
"output": "This is content",
"reasoning_content": "This is content",
"content": None,
"is_reasoning_end": False,
}
NO_REASONING_STREAMING = {
"output": "This is a reasoning section",
"reasoning_content": "This is a reasoning section",
"content": None,
"is_reasoning_end": False,
}
MULTIPLE_LINES = {
"output": "This\nThat</think>This is the rest\nThat",
"reasoning_content": "This\nThat",
"content": "This is the rest\nThat",
"is_reasoning_end": True,
}
SHORTEST_REASONING_NO_STREAMING = {
"output": "</think>This is the rest",
"reasoning_content": None,
"content": "This is the rest",
"is_reasoning_end": True,
}
SHORTEST_REASONING = {
"output": "</think>This is the rest",
"reasoning_content": None,
"content": "This is the rest",
"is_reasoning_end": True,
}
REASONING_WITH_THINK = {
"output": "<think>This is a reasoning section</think>This is the rest",
"reasoning_content": "This is a reasoning section",
"content": "This is the rest",
"is_reasoning_end": True,
}
COMPLETE_REASONING_WITH_THINK = {
"output": "<think>This is a reasoning section</think>",
"reasoning_content": "This is a reasoning section",
"content": None,
"is_reasoning_end": False,
}
MULTIPLE_LINES_WITH_THINK = {
"output": "<think>This\nThat</think>This is the rest\nThat",
"reasoning_content": "This\nThat",
"content": "This is the rest\nThat",
"is_reasoning_end": True,
}
SHORTEST_REASONING_NO_STREAMING_WITH_THINK = {
"output": "</think>This is the rest",
"reasoning_content": None,
"content": "This is the rest",
"is_reasoning_end": True,
}
SHORTEST_REASONING_WITH_THINK = {
"output": "</think>This is the rest",
"reasoning_content": None,
"content": "This is the rest",
"is_reasoning_end": True,
}
THINK_NO_END = {
"output": "<think>This is a reasoning section",
"reasoning_content": "This is a reasoning section",
"content": None,
"is_reasoning_end": False,
}
EMPTY = {
"output": "",
"reasoning_content": None,
"content": None,
"is_reasoning_end": False,
}
EMPTY_STREAMING = {
"output": "",
"reasoning_content": None,
"content": None,
"is_reasoning_end": False,
}
NEW_LINE = {
"output": "\n<think>This is a reasoning section</think>\nThis is the rest",
"reasoning_content": "This is a reasoning section",
"content": "This is the rest",
"is_reasoning_end": True,
}

NEW_LINE_STREAMING = {
"output": "\n<think>This is a reasoning section\n</think>\nThis is the rest",
"reasoning_content": "\nThis is a reasoning section",
"content": "This is the rest",
"is_reasoning_end": True,
}

NEW_LINE_STREAMING_COMPLEX_CONTENT = {
"output": "\n This is a \n reasoning section\n\n\n</think>\n\nThis is the rest",
"reasoning_content": "\n This is a \n reasoning section\n\n",
"content": "\nThis is the rest",
"is_reasoning_end": True,
}

MULTI_TURN_PROMPT_CONTENT = {
"output": "<think> This is last turn's reasoning section </think> hello <think>",
"reasoning_content": "",
"content": "",
"is_reasoning_end": False,
}

TEST_CASES = [
pytest.param(
False,
SIMPLE_REASONING,
id="simple_reasoning",
),
pytest.param(
True,
SIMPLE_REASONING,
id="simple_reasoning_streaming",
),
pytest.param(
False,
COMPLETE_REASONING,
id="complete_reasoning",
),
pytest.param(
True,
COMPLETE_REASONING,
id="complete_reasoning_streaming",
),
pytest.param(
False,
NO_CONTENT,
id="no_content_token",
),
pytest.param(
True,
NO_REASONING_STREAMING,
id="no_reasoning_token_streaming",
),
pytest.param(
False,
MULTIPLE_LINES,
id="multiple_lines",
),
pytest.param(
True,
MULTIPLE_LINES,
id="multiple_lines_streaming",
),
pytest.param(
True,
SHORTEST_REASONING,
id="shortest",
),
pytest.param(
False,
SHORTEST_REASONING_NO_STREAMING,
id="shortest_streaming",
),
pytest.param(
False,
REASONING_WITH_THINK,
id="reasoning_with_think",
),
pytest.param(
True,
REASONING_WITH_THINK,
id="reasoning_with_think_streaming",
),
pytest.param(
False,
COMPLETE_REASONING_WITH_THINK,
id="complete_reasoning_with_think",
),
pytest.param(
True,
COMPLETE_REASONING_WITH_THINK,
id="complete_reasoning_with_think_streaming",
),
pytest.param(
False,
MULTIPLE_LINES_WITH_THINK,
id="multiple_lines_with_think",
),
pytest.param(
True,
MULTIPLE_LINES_WITH_THINK,
id="multiple_lines_with_think_streaming",
),
pytest.param(
False,
SHORTEST_REASONING_NO_STREAMING_WITH_THINK,
id="shortest_with_think",
),
pytest.param(
True,
SHORTEST_REASONING_WITH_THINK,
id="shortest_with_think_streaming",
),
pytest.param(
False,
THINK_NO_END,
id="think_no_end",
),
pytest.param(
True,
THINK_NO_END,
id="think_no_end_streaming",
),
pytest.param(
False,
EMPTY,
id="empty",
),
pytest.param(
True,
EMPTY_STREAMING,
id="empty_streaming",
),
pytest.param(
False,
NEW_LINE,
id="new_line",
),
pytest.param(
True,
NEW_LINE_STREAMING,
id="new_line_streaming",
),
pytest.param(
True,
NEW_LINE_STREAMING_COMPLEX_CONTENT,
id="new_line_streaming_complex_content",
),
pytest.param(
True,
MULTI_TURN_PROMPT_CONTENT,
id="multi_turn_prompt_content",
),
]


@pytest.mark.parametrize("streaming, param_dict", TEST_CASES)
def test_reasoning(
streaming: bool,
param_dict: dict,
step3p5_tokenizer,
request,
):
output = step3p5_tokenizer.tokenize(param_dict["output"])
# decode everything to tokens
output_tokens: list[str] = [
step3p5_tokenizer.convert_tokens_to_string([token]) for token in output
]
parser: ReasoningParser = ReasoningParserManager.get_reasoning_parser(parser_name)(
step3p5_tokenizer
)

reasoning, content = run_reasoning_extraction(
parser, output_tokens, streaming=streaming
)

print(f"reasoning: {reasoning}")
print(f"content: {content}")
test_id = request.node.callspec.id if hasattr(request.node, "callspec") else None
if request.node.callspec.id != "multi_turn_prompt_content":
assert reasoning == param_dict["reasoning_content"]
assert content == param_dict["content"]

# Test is_reasoning_end
output_ids = step3p5_tokenizer.convert_tokens_to_ids(output)
if streaming:
is_reasoning_end = parser.is_reasoning_end(output_ids)
assert is_reasoning_end == param_dict["is_reasoning_end"]
Comment on lines +304 to +306
Copy link
Contributor

@gemini-code-assist gemini-code-assist bot Feb 10, 2026

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

high

The test for is_reasoning_end in streaming mode is not correctly testing the streaming behavior. It calls the non-streaming parser.is_reasoning_end(output_ids) method, which evaluates the entire output at once. The stateful, incremental logic of is_reasoning_end_streaming which operates on delta_ids is not being exercised. This is a significant testing gap for a critical part of the bug fix.

To properly test the streaming logic, you should simulate the streaming process and call is_reasoning_end_streaming at each step. Here is an example of how you could structure such a test:

def run_is_reasoning_end_streaming(parser, output_ids):
    is_end = False
    current_ids = []
    for token_id in output_ids:
        delta_ids = [token_id]
        current_ids.append(token_id)
        is_end = parser.is_reasoning_end_streaming(current_ids, delta_ids)
    return is_end

# In test_reasoning, under the `if streaming:` block:
streaming_parser = ReasoningParserManager.get_reasoning_parser(parser_name)(step3p5_tokenizer)
is_reasoning_end = run_is_reasoning_end_streaming(streaming_parser, output_ids)
assert is_reasoning_end == param_dict["is_reasoning_end"]

This would ensure the state transitions of the parser are correctly handled in streaming mode.


# Test extract_content
if param_dict["content"] is not None:
content = parser.extract_content_ids(output_ids)
# Fixed expected token ids for specific test cases
test_id = (
request.node.callspec.id if hasattr(request.node, "callspec") else None
)
# Match most specific first
if test_id not in [
"new_line_streaming_complex_content",
"new_line_streaming",
"new_line",
"multi_turn_prompt_content",
]:
expected_content_ids = step3p5_tokenizer.convert_tokens_to_ids(
step3p5_tokenizer.tokenize(param_dict["content"])
)
assert content == expected_content_ids
else:
content = parser.extract_content_ids(output)
assert content == []


def test_step3p5_streaming_drops_leading_newline(step3p5_tokenizer):
parser_cls = ReasoningParserManager.get_reasoning_parser("step3p5")
parser = parser_cls(step3p5_tokenizer)
output = "<think>calc</think>\nAnswer"
tokens = step3p5_tokenizer.tokenize(output)
output_tokens = [
step3p5_tokenizer.convert_tokens_to_string([token]) for token in tokens
]

_, content = run_reasoning_extraction(parser, output_tokens, streaming=True)
assert content == "Answer"
Loading