diff --git a/tests/build_cython.py b/tests/build_cython.py
deleted file mode 100644
index 444434e8f0a79..0000000000000
--- a/tests/build_cython.py
+++ /dev/null
@@ -1,39 +0,0 @@
-# SPDX-License-Identifier: Apache-2.0
-# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
-import Cython.Compiler.Options
-from Cython.Build import cythonize
-from setuptools import setup
-
-Cython.Compiler.Options.annotate = True
-
-infiles = []
-
-infiles += [
-    "vllm/engine/llm_engine.py",
-    "vllm/transformers_utils/detokenizer.py",
-    "vllm/engine/output_processor/single_step.py",
-    "vllm/outputs.py",
-    "vllm/engine/output_processor/stop_checker.py",
-]
-
-infiles += [
-    "vllm/core/scheduler.py",
-    "vllm/sequence.py",
-    "vllm/core/block_manager.py",
-]
-
-infiles += [
-    "vllm/model_executor/layers/sampler.py",
-    "vllm/sampling_params.py",
-    "vllm/utils/__init__.py",
-]
-
-setup(ext_modules=cythonize(infiles,
-                            annotate=False,
-                            force=True,
-                            compiler_directives={
-                                'language_level': "3",
-                                'infer_types': True
-                            }))
-
-# example usage: python3 build_cython.py build_ext --inplace
diff --git a/vllm/engine/output_processor/__init__.py b/vllm/engine/output_processor/__init__.py
deleted file mode 100644
index e69de29bb2d1d..0000000000000
diff --git a/vllm/engine/output_processor/interfaces.py b/vllm/engine/output_processor/interfaces.py
deleted file mode 100644
index 587a9221e32c8..0000000000000
--- a/vllm/engine/output_processor/interfaces.py
+++ /dev/null
@@ -1,59 +0,0 @@
-# SPDX-License-Identifier: Apache-2.0
-# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
-
-from abc import ABC, abstractmethod
-from typing import List
-
-from vllm.config import SchedulerConfig
-from vllm.core.scheduler import Scheduler
-from vllm.engine.output_processor.stop_checker import StopChecker
-from vllm.sequence import SequenceGroup, SequenceGroupOutput
-from vllm.transformers_utils.detokenizer import Detokenizer
-from vllm.utils import Counter
-
-
-class SequenceGroupOutputProcessor(ABC):
-    """Interface for logic that processes new token ids in sequence groups,
-    managing detokenization, stop checking, and freeing/forking sequences with
-    the scheduler.
-
-    This is highly coupled with the LLMEngine and should be seen as an extension
-    of it. The logic is separated to simplify the LLMEngine class and allow
-    separate implementations for single-step decoding (which supports beam
-    search sequence forking) and multi-step decoding (which does not support
-    beam search, but does support speculative decoding).
-    """
-
-    @staticmethod
-    def create_output_processor(
-        scheduler_config: SchedulerConfig,
-        detokenizer: Detokenizer,
-        scheduler: List[Scheduler],
-        seq_counter: Counter,
-        stop_checker: "StopChecker",
-    ):
-        """Create an output processor.
-
-        Multi-step scheduling is no longer supported. Always return a
-        single-step output processor.
-        """
-        from vllm.engine.output_processor.single_step import (
-            SingleStepOutputProcessor)
-        return SingleStepOutputProcessor(scheduler_config, detokenizer,
-                                         scheduler, seq_counter, stop_checker)
-
-    @abstractmethod
-    def process_outputs(self, sequence_group: SequenceGroup,
-                        outputs: List[SequenceGroupOutput],
-                        is_async: bool) -> None:
-        """Process new token ids for the sequence group. Handles logic such as
-        detokenization, stop checking, and freeing/forking sequences in the
-        scheduler.
-        """
-        pass
-
-    @abstractmethod
-    def process_prompt_logprob(self, seq_group: SequenceGroup,
-                               outputs: List[SequenceGroupOutput]) -> None:
-        """Update prompt logprobs received from outputs to seq_group."""
-        pass
diff --git a/vllm/engine/output_processor/single_step.py b/vllm/engine/output_processor/single_step.py
deleted file mode 100644
index dbf6a371d050a..0000000000000
--- a/vllm/engine/output_processor/single_step.py
+++ /dev/null
@@ -1,145 +0,0 @@
-# SPDX-License-Identifier: Apache-2.0
-# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
-
-from typing import List
-
-from vllm.config import SchedulerConfig
-from vllm.core.scheduler import Scheduler
-from vllm.engine.output_processor.interfaces import (
-    SequenceGroupOutputProcessor)
-from vllm.engine.output_processor.stop_checker import StopChecker
-from vllm.logger import init_logger
-from vllm.sequence import (CompletionSequenceGroupOutput, SequenceGroup,
-                           SequenceGroupOutput)
-from vllm.transformers_utils.detokenizer import Detokenizer
-from vllm.utils import Counter
-
-logger = init_logger(__name__)
-
-
-def single_step_process_prompt_logprob(
-        sg_output_proc: SequenceGroupOutputProcessor, seq_group: SequenceGroup,
-        output: CompletionSequenceGroupOutput) -> None:
-    """Process prompt logprobs associated with the
-    [`SequenceGroupOutput`][vllm.sequence.SequenceGroupOutput] for a given step.
-
-    Do nothing if the output has no prompt logprobs.
-
-    Account for the fact that transformers do not compute first-token logprobs.
-    
-    Args:
-      sg_output_proc:
-          [`SequenceGroupOutputProcessor`][vllm.engine.output_processor.interfaces.SequenceGroupOutputProcessor]
-          instance
-      seq_group: the output is associated with this
-          [`SequenceGroup`][vllm.sequence.SequenceGroup]
-      output: the [`SequenceGroupOutput`][vllm.sequence.SequenceGroupOutput]
-          for a single scheduler step
-    """
-    prompt_logprobs = output.prompt_logprobs
-
-    # If this is the first (or only) "chunk" of the prefill, we need
-    # to prepend None to the list of prompt logprobs. The reason for this
-    # is that for N prompt tokens, the Sampler will generate N-1 total
-    # prompt logprobs during prefill since the token at idx 0 will not
-    # have a logprob associated with it.
-    if prompt_logprobs is not None:
-        if not seq_group.prompt_logprobs:
-            prompt_logprobs = [None] + prompt_logprobs
-            seq_group.prompt_logprobs = []
-
-        assert hasattr(sg_output_proc, 'detokenizer')
-        if (seq_group.sampling_params.detokenize
-                and sg_output_proc.detokenizer):
-            sg_output_proc.detokenizer.decode_prompt_logprobs_inplace(
-                seq_group,
-                prompt_logprobs,
-                position_offset=len(seq_group.prompt_logprobs))
-
-        seq_group.prompt_logprobs.extend(prompt_logprobs)
-
-
-class SingleStepOutputProcessor(SequenceGroupOutputProcessor):
-    """SequenceGroupOutputProcessor which handles "output processing" logic,
-    which happens after the model returns generated token ids and before
-    scheduling of the next batch. Output processing logic includes
-    detokenization, and determining if a sequence is finished (e.g. via max len
-    or eos token).
-
-    The SingleStepOutputProcessor is specialized to the case where the model
-    emits at most a single token per invocation, which precludes configurations
-    such as speculative decoding or multi-step decoding. This enables beam
-    search sampling, which requires forking/finishing/freeing sequences in a way
-    that is currently difficult to schedule multiple steps ahead of time.
-    """
-
-    def __init__(self, scheduler_config: SchedulerConfig,
-                 detokenizer: Detokenizer, scheduler: List[Scheduler],
-                 seq_counter: Counter, stop_checker: StopChecker):
-        self.scheduler_config = scheduler_config
-        self.detokenizer = detokenizer
-        self.scheduler = scheduler
-        self.seq_counter = seq_counter
-        self.stop_checker = stop_checker
-
-    def process_outputs(self, sequence_group: SequenceGroup,
-                        outputs: List[SequenceGroupOutput],
-                        is_async: bool) -> None:
-        """Append all new tokens to sequences in the sequence group. Fork any
-        surviving beam candidates; free any unsurviving ones.
-
-        Invokes detokenizer to detokenize new tokens, and also marks sequences
-        as finished if they meet stop conditions.
-        
-        is_async - Indicates whether this postprocessor runs in 
-            parallel with the GPU forward pass and is processing 
-            tokens from the previous step. If this is true, then
-            no tokens need to be appended since it is already done
-            externally (before the next schedule() call)
-        """
-        assert (len(outputs) == 1
-                ), f"{type(self)} does not support multiple outputs per step"
-        return self._process_sequence_group_outputs(sequence_group, outputs[0],
-                                                    is_async)
-
-    def process_prompt_logprob(self, seq_group: SequenceGroup,
-                               outputs: List[SequenceGroupOutput]) -> None:
-        """Process prompt logprobs associated with one step of a single-step-
-        scheduled computation.
-        
-        Args:
-          seq_group: the output is associated with this
-              [`SequenceGroup`][vllm.sequence.SequenceGroup]
-          outputs: the
-              [`SequenceGroupOutput`][vllm.sequence.SequenceGroupOutput]
-              for a single scheduler step
-        """
-        assert len(outputs) == 1, "Single step should only have 1 output."
-        output = outputs[0]
-        assert isinstance(output, CompletionSequenceGroupOutput)
-        single_step_process_prompt_logprob(self, seq_group, output)
-
-    def _process_sequence_group_outputs(self, seq_group: SequenceGroup,
-                                        outputs: SequenceGroupOutput,
-                                        is_async: bool) -> None:
-        sampling_params = seq_group.sampling_params
-
-        sample = outputs.samples[0]
-        seq = seq_group.first_seq
-        if not is_async:
-            seq.append_token_id(sample.output_token, sample.logprobs,
-                                sample.output_embed)
-        if sampling_params.detokenize and self.detokenizer:
-            new_char_count = self.detokenizer.decode_sequence_inplace(
-                seq, sampling_params)
-        else:
-            new_char_count = 0
-        self.stop_checker.maybe_stop_sequence(
-            seq,
-            new_char_count,
-            sampling_params,
-            lora_req=seq_group.lora_request,
-        )
-        if seq.is_finished():
-            for scheduler in self.scheduler:
-                scheduler.free_seq(seq)
diff --git a/vllm/engine/output_processor/stop_checker.py b/vllm/engine/output_processor/stop_checker.py
deleted file mode 100644
index 0916f1c918c85..0000000000000
--- a/vllm/engine/output_processor/stop_checker.py
+++ /dev/null
@@ -1,139 +0,0 @@
-# SPDX-License-Identifier: Apache-2.0
-# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
-
-from typing import List, Optional, Tuple
-
-from vllm.lora.request import LoRARequest
-from vllm.reasoning import ReasoningParser
-from vllm.sampling_params import SamplingParams
-from vllm.sequence import Sequence, SequenceStatus
-
-
-class StopChecker:
-    """LLMEngine helper class which separates out the logic involving stop
-    checking. This checks things such as: whether the eos token was emitted,
-    whether the max_tokens has been consumed, whether a stop string has been
-    emitted, or if we have exceeded the max model len.
-    """
-
-    def __init__(
-        self,
-        max_model_len: int,
-        reasoner: Optional[ReasoningParser] = None,
-    ):
-        # Do not use it directly, but use `self._get_max_model_len`.
-        self._max_model_len = max_model_len
-        self.reasoner = reasoner
-
-    def _get_max_model_len(self, lora_req: Optional[LoRARequest]):
-        if lora_req and lora_req.long_lora_max_len:
-            return lora_req.long_lora_max_len
-        else:
-            return self._max_model_len
-
-    def maybe_stop_sequence(
-        self,
-        seq: Sequence,
-        new_char_count: int,
-        sampling_params: SamplingParams,
-        lora_req: Optional[LoRARequest] = None,
-    ) -> None:
-        """Stop the finished sequences.
-
-       new_char_count is the number of chars added to the
-           sequence's output text for the newly generated token
-        """
-
-        # Check if the minimum number of tokens has been generated yet;
-        # skip the stop string/token checks if not
-        if seq.get_output_len() < sampling_params.min_tokens:
-            return
-
-        # Check if the sequence has generated the EOS token.
-        if ((not sampling_params.ignore_eos)
-                and seq.get_last_token_id() == seq.eos_token_id):
-            # Remove the last EOS token unless explicitly specified
-            # This prevents unintended exposure of the EOS token
-            if new_char_count and (
-                    not sampling_params.include_stop_str_in_output):
-                seq.output_text = seq.output_text[:-new_char_count]
-            seq.status = SequenceStatus.FINISHED_STOPPED
-            return
-
-        # Skip stop string/token checks if in reasoning content generation
-        if self.reasoner is not None and \
-            not self.reasoner.is_reasoning_end(seq.get_token_ids()):
-            return
-
-        # Check if a stop token was encountered.
-        # This assumes a single token produced per step.
-        last_token_id = seq.get_last_token_id()
-        if last_token_id in (sampling_params.stop_token_ids or ()):
-            if new_char_count and (
-                    not sampling_params.include_stop_str_in_output):
-                # Remove last token
-                seq.output_text = seq.output_text[:-new_char_count]
-            seq.status = SequenceStatus.FINISHED_STOPPED
-            seq.stop_reason = last_token_id
-            return
-
-        # Check if any stop strings are matched.
-        stop = self.check_stop_strings(
-            seq.output_text, new_char_count, sampling_params.stop,
-            sampling_params.include_stop_str_in_output)
-        if stop is not None:
-            stop_str, truncate_to = stop
-            if truncate_to != -1:
-                seq.output_text = seq.output_text[:truncate_to]
-            seq.status = SequenceStatus.FINISHED_STOPPED
-            seq.stop_reason = stop_str
-            return
-
-        # Check if the sequence has reached max_model_len.
-        if seq.get_len() >= self._get_max_model_len(lora_req):
-            seq.status = SequenceStatus.FINISHED_LENGTH_CAPPED
-            return
-
-        # Check if the sequence has reached max_tokens.
-        if seq.get_output_len() == sampling_params.max_tokens:
-            seq.status = SequenceStatus.FINISHED_LENGTH_CAPPED
-            return
-
-    @staticmethod
-    def check_stop_strings(
-        output_text: str,
-        new_char_count: int,
-        stop: List[str],
-        include_in_output: bool,
-    ) -> Optional[Tuple[str, int]]:
-        """Check if any stop strings are matched and truncate sequence
-        output text accordingly.
-
-        Returns tuple (stop_string, offset) if matched or else None.
-
-        Where stop_string is the matched stop string and offset is the
-        length to which output_text should be truncated, or -1 for no
-        truncation.
-        """
-        if not new_char_count or not stop:
-            return None
-
-        for stop_str in stop:
-            stop_string_len = len(stop_str)
-            # Avoid searching already-searched text.
-            stop_index = output_text.find(stop_str,
-                                          1 - new_char_count - stop_string_len)
-            if stop_index == -1:
-                continue
-
-            if include_in_output:
-                # Truncate to end of stop string.
-                stop_index += stop_string_len
-                if stop_index >= len(output_text):
-                    # No truncation required.
-                    return stop_str, -1
-
-            # Truncate the output text to either the beginning
-            # or end of the stop string.
-            return stop_str, stop_index
-        return None
diff --git a/vllm/v1/engine/detokenizer.py b/vllm/v1/engine/detokenizer.py
index 8aa36d6a439c1..0f993a74c8103 100644
--- a/vllm/v1/engine/detokenizer.py
+++ b/vllm/v1/engine/detokenizer.py
@@ -9,7 +9,6 @@ from tokenizers import Tokenizer
 from tokenizers.decoders import DecodeStream
 from transformers import PreTrainedTokenizerFast
 
-from vllm.engine.output_processor.stop_checker import StopChecker
 from vllm.logger import init_logger
 from vllm.transformers_utils.detokenizer_utils import (
     AnyTokenizer, convert_prompt_ids_to_tokens, detokenize_incrementally)
@@ -129,7 +128,7 @@ class BaseIncrementalDetokenizer(IncrementalDetokenizer, ABC):
         # 2) Evaluate stop strings.
         stop_string = None
         if self.stop and len(self.output_token_ids) > self.min_tokens:
-            stop = StopChecker.check_stop_strings(
+            stop = check_stop_strings(
                 output_text=self.output_text,
                 new_char_count=len(self.output_text) - stop_check_offset,
                 stop=self.stop,
@@ -309,3 +308,42 @@ class SlowIncrementalDetokenizer(BaseIncrementalDetokenizer):
         self.read_offset = read_offset
 
         return decoded_text
+
+
+def check_stop_strings(
+    output_text: str,
+    new_char_count: int,
+    stop: list[str],
+    include_in_output: bool,
+) -> Optional[tuple[str, int]]:
+    """Check if any stop strings are matched and truncate sequence
+    output text accordingly.
+
+    Returns tuple (stop_string, offset) if matched or else None.
+
+    Where stop_string is the matched stop string and offset is the
+    length to which output_text should be truncated, or -1 for no
+    truncation.
+    """
+    if not new_char_count or not stop:
+        return None
+
+    for stop_str in stop:
+        stop_string_len = len(stop_str)
+        # Avoid searching already-searched text.
+        stop_index = output_text.find(stop_str,
+                                      1 - new_char_count - stop_string_len)
+        if stop_index == -1:
+            continue
+
+        if include_in_output:
+            # Truncate to end of stop string.
+            stop_index += stop_string_len
+            if stop_index >= len(output_text):
+                # No truncation required.
+                return stop_str, -1
+
+        # Truncate the output text to either the beginning
+        # or end of the stop string.
+        return stop_str, stop_index
+    return None