feat: add --disaggregation-mode enum to vLLM backend (#6483)

Signed-off-by: alec-flowers <aflowers@nvidia.com>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

benchmarks/router/run_engines.sh

@@ -186,10 +186,10 @@ if [ "$USE_MOCKERS" = true ]; then
     # Set endpoint based on worker mode
     if [ "$MODE" = "prefill" ]; then
         MOCKER_ARGS+=("--endpoint" "dyn://test.prefill.generate")
-        MOCKER_ARGS+=("--is-prefill-worker")
+        MOCKER_ARGS+=("--disaggregation-mode" "prefill")
     elif [ "$MODE" = "decode" ]; then
         MOCKER_ARGS+=("--endpoint" "dyn://test.mocker.generate")
-        MOCKER_ARGS+=("--is-decode-worker")
+        MOCKER_ARGS+=("--disaggregation-mode" "decode")
     else
         MOCKER_ARGS+=("--endpoint" "dyn://test.mocker.generate")
     fi
@@ -254,9 +254,9 @@ else
                     VLLM_ARGS+=("--data-parallel-size" "$DATA_PARALLEL_SIZE")
                 fi
                 if [ "$MODE" = "prefill" ]; then
-                    VLLM_ARGS+=("--is-prefill-worker")
+                    VLLM_ARGS+=("--disaggregation-mode" "prefill")
                 elif [ "$MODE" = "decode" ]; then
-                    VLLM_ARGS+=("--is-decode-worker")
+                    VLLM_ARGS+=("--disaggregation-mode" "decode")
                 fi
                 VLLM_ARGS+=("${EXTRA_ARGS[@]}")
 

components/src/dynamo/common/__init__.py

@@ -12,7 +12,7 @@ Main submodules:
     - utils: Common utilities including environment and prometheus helpers
 """
 
-from dynamo.common import config_dump, utils
+from dynamo.common import config_dump, constants, utils
 
 try:
     from ._version import __version__
@@ -24,4 +24,4 @@ except Exception:
     except Exception:
         __version__ = "0.0.0+unknown"
 
-__all__ = ["__version__", "config_dump", "utils"]
+__all__ = ["__version__", "config_dump", "constants", "utils"]

components/src/dynamo/common/constants.py

+# SPDX-FileCopyrightText: Copyright (c) 2025-2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
+# SPDX-License-Identifier: Apache-2.0
+
+"""Shared constants for Dynamo backends."""
+
+from enum import Enum
+
+
+class DisaggregationMode(Enum):
+    """Disaggregation mode for LLM workers."""
+
+    AGGREGATED = "agg"
+    PREFILL = "prefill"
+    DECODE = "decode"

components/src/dynamo/mocker/README.md

@@ -26,7 +26,7 @@ The mocker engine now supports a vLLM-style CLI interface with individual argume
 - `--data-parallel-size`: Number of data parallel workers to simulate (default: 1)
 - `--num-workers`: Number of mocker workers to launch in the same process (default: 1). All workers share the same tokio runtime and thread pool
 - `--stagger-delay`: Delay in seconds between launching each worker to avoid overwhelming etcd/NATS/frontend. Set to 0 to disable staggering. Use -1 for auto mode (stagger dependent on number of workers). Default: -1 (auto)
-- `--is-prefill-worker` / `--is-decode-worker`: Whether the worker is a prefill or decode worker for disaggregated deployment. If not specified, mocker will be in aggregated mode.
+- `--disaggregation-mode prefill` / `--disaggregation-mode decode`: Whether the worker is a prefill or decode worker for disaggregated deployment. If not specified, mocker will be in aggregated mode.
 
 **Environment variables:**
 

components/src/dynamo/mocker/args.py

@@ -142,14 +142,48 @@ def create_temp_engine_args_file(args) -> Path:
 
 def validate_worker_type_args(args):
     """
-    Validate that is_prefill_worker and is_decode_worker are not both True.
+    Resolve disaggregation mode from --disaggregation-mode or legacy boolean flags.
     Raises ValueError if validation fails.
     """
+    import warnings
+
+    explicit_mode = args.disaggregation_mode is not None
+    has_legacy = args.is_prefill_worker or args.is_decode_worker
+
+    if has_legacy and explicit_mode:
+        raise ValueError(
+            "Cannot combine --is-prefill-worker/--is-decode-worker with "
+            "--disaggregation-mode. Use only --disaggregation-mode."
+        )
+
+    if has_legacy:
         if args.is_prefill_worker and args.is_decode_worker:
             raise ValueError(
                 "Cannot specify both --is-prefill-worker and --is-decode-worker. "
                 "A worker must be either prefill, decode, or aggregated (neither flag set)."
             )
+        if args.is_prefill_worker:
+            warnings.warn(
+                "--is-prefill-worker is deprecated, use --disaggregation-mode=prefill",
+                DeprecationWarning,
+                stacklevel=2,
+            )
+            args.disaggregation_mode = "prefill"
+        elif args.is_decode_worker:
+            warnings.warn(
+                "--is-decode-worker is deprecated, use --disaggregation-mode=decode",
+                DeprecationWarning,
+                stacklevel=2,
+            )
+            args.disaggregation_mode = "decode"
+
+    # Apply default if neither new flag nor legacy flags were provided
+    if args.disaggregation_mode is None:
+        args.disaggregation_mode = "agg"
+
+    # Sync booleans from disaggregation_mode
+    args.is_prefill_worker = args.disaggregation_mode == "prefill"
+    args.is_decode_worker = args.disaggregation_mode == "decode"
 
 
 def parse_bootstrap_ports(ports_str: str | None) -> list[int]:
@@ -305,17 +339,27 @@ def parse_args():
     )
 
     # Worker type configuration
+    parser.add_argument(
+        "--disaggregation-mode",
+        type=str,
+        default=None,
+        choices=["agg", "prefill", "decode"],
+        help="Worker disaggregation mode: 'agg' (default, aggregated), "
+        "'prefill' (prefill-only worker), or 'decode' (decode-only worker).",
+    )
     parser.add_argument(
         "--is-prefill-worker",
         action="store_true",
         default=False,
-        help="Register as Prefill model type instead of Chat+Completions (default: False)",
+        help="DEPRECATED: use --disaggregation-mode=prefill. "
+        "Register as Prefill model type instead of Chat+Completions (default: False)",
     )
     parser.add_argument(
         "--is-decode-worker",
         action="store_true",
         default=False,
-        help="Mark this as a decode worker which does not publish KV events and skips prefill cost estimation (default: False)",
+        help="DEPRECATED: use --disaggregation-mode=decode. "
+        "Mark this as a decode worker which does not publish KV events (default: False)",
     )
     parser.add_argument(
         "--durable-kv-events",

components/src/dynamo/profiler/utils/config_modifiers/vllm.py

@@ -108,7 +108,8 @@ class VllmV1ConfigModifier(BaseConfigModifier):
             args = validate_and_get_worker_args(worker_service, backend="vllm")
             args = break_arguments(args)
 
-            # remove --is-prefill-worker flag
+            # remove --disaggregation-mode and its value (or legacy --is-prefill-worker)
+            args = remove_valued_arguments(args, "--disaggregation-mode")
             if "--is-prefill-worker" in args:
                 args.remove("--is-prefill-worker")
 

components/src/dynamo/router/README.md

@@ -67,7 +67,7 @@ python -m dynamo.router \
 python -m dynamo.vllm --model MODEL_NAME --block-size 64 &
 
 # Start prefill workers
-python -m dynamo.vllm --model MODEL_NAME --block-size 64 --is-prefill-worker &
+python -m dynamo.vllm --model MODEL_NAME --block-size 64 --disaggregation-mode prefill &
 ```
 
 >[!Note]

components/src/dynamo/sglang/args.py

@@ -9,7 +9,6 @@ import socket
 import sys
 import tempfile
 from argparse import Namespace
-from enum import Enum
 from pathlib import Path
 from typing import Any, Dict, Generator, Optional
 
@@ -20,6 +19,7 @@ from sglang.srt.server_args_config_parser import ConfigArgumentMerger
 from dynamo.common.config_dump import register_encoder
 from dynamo.common.configuration.groups import DynamoRuntimeConfig
 from dynamo.common.configuration.groups.runtime_args import DynamoRuntimeArgGroup
+from dynamo.common.constants import DisaggregationMode
 from dynamo.common.utils.runtime import parse_endpoint
 from dynamo.llm import fetch_model
 from dynamo.runtime.logging import configure_dynamo_logging
@@ -28,12 +28,6 @@ from dynamo.sglang.backend_args import DynamoSGLangArgGroup, DynamoSGLangConfig
 configure_dynamo_logging()
 
 
-class DisaggregationMode(Enum):
-    AGGREGATED = "agg"
-    PREFILL = "prefill"
-    DECODE = "decode"
-
-
 class DynamoConfig(DynamoRuntimeConfig, DynamoSGLangConfig):
     """Combined configuration container for SGLang server and Dynamo args."""
 

components/src/dynamo/sglang/main.py

@@ -16,6 +16,7 @@ import uvloop
 
 from dynamo import prometheus_names
 from dynamo.common.config_dump import dump_config
+from dynamo.common.constants import DisaggregationMode
 from dynamo.common.storage import get_fs
 from dynamo.common.utils.endpoint_types import parse_endpoint_types
 from dynamo.common.utils.graceful_shutdown import graceful_shutdown_with_discovery
@@ -23,7 +24,7 @@ from dynamo.common.utils.runtime import create_runtime
 from dynamo.llm import ModelInput, ModelType
 from dynamo.runtime import DistributedRuntime
 from dynamo.runtime.logging import configure_dynamo_logging
-from dynamo.sglang.args import Config, DisaggregationMode, parse_args
+from dynamo.sglang.args import Config, parse_args
 from dynamo.sglang.health_check import (
     ImageDiffusionHealthCheckPayload,
     SglangHealthCheckPayload,

components/src/dynamo/sglang/request_handlers/llm/decode_handler.py

@@ -9,8 +9,9 @@ from typing import Any, AsyncGenerator, Dict, Optional
 import sglang as sgl
 
 from dynamo._core import Context
+from dynamo.common.constants import DisaggregationMode
 from dynamo.common.utils.engine_response import normalize_finish_reason
-from dynamo.sglang.args import Config, DisaggregationMode
+from dynamo.sglang.args import Config
 from dynamo.sglang.publisher import DynamoSglangPublisher
 from dynamo.sglang.request_handlers.handler_base import BaseWorkerHandler
 

components/src/dynamo/sglang/request_handlers/multimodal/worker_handler.py

@@ -11,8 +11,9 @@ import torch
 
 import dynamo.nixl_connect as connect
 from dynamo._core import Client, Context
+from dynamo.common.constants import DisaggregationMode
 from dynamo.common.utils.engine_response import normalize_finish_reason
-from dynamo.sglang.args import Config, DisaggregationMode
+from dynamo.sglang.args import Config
 from dynamo.sglang.protocol import (
     DisaggSglangMultimodalRequest,
     SglangMultimodalRequest,

components/src/dynamo/vllm/args.py

@@ -24,6 +24,7 @@ from dynamo.common.configuration.groups.runtime_args import (
 )
 from dynamo.common.utils.runtime import parse_endpoint
 from dynamo.vllm.backend_args import DynamoVllmArgGroup, DynamoVllmConfig
+from dynamo.vllm.constants import DisaggregationMode
 
 from . import envs
 
@@ -35,8 +36,6 @@ VALID_CONNECTORS = {"nixl", "lmcache", "kvbm", "null", "none"}
 
 class Config(DynamoRuntimeConfig, DynamoVllmConfig):
     component: str
-    is_prefill_worker: bool
-    is_decode_worker: bool
     custom_jinja_template: Optional[str] = None
     discovery_backend: str
     request_plane: str
@@ -157,7 +156,6 @@ def update_dynamo_config_with_engine(
     # Capture user-provided --endpoint before defaults overwrite it
     user_endpoint = dynamo_config.endpoint
 
-    # TODO: move to "disaggregation_mode" as the other engines.
     if dynamo_config.route_to_encoder:
         dynamo_config.component = "processor"
         dynamo_config.endpoint = "generate"
@@ -167,13 +165,16 @@ def update_dynamo_config_with_engine(
     elif dynamo_config.multimodal_decode_worker:
         dynamo_config.component = "decoder"
         dynamo_config.endpoint = "generate"
-    elif dynamo_config.multimodal_worker and dynamo_config.is_prefill_worker:
+    elif (
+        dynamo_config.multimodal_worker
+        and dynamo_config.disaggregation_mode == DisaggregationMode.PREFILL
+    ):
         dynamo_config.component = "backend"
         dynamo_config.endpoint = "generate"
     elif dynamo_config.omni:
         dynamo_config.component = "backend"
         dynamo_config.endpoint = "generate"
-    elif dynamo_config.is_prefill_worker:
+    elif dynamo_config.disaggregation_mode == DisaggregationMode.PREFILL:
         dynamo_config.component = "prefill"
         dynamo_config.endpoint = "generate"
     else:
@@ -320,10 +321,10 @@ def create_kv_events_config(
     dynamo_config: Config, engine_config: AsyncEngineArgs
 ) -> Optional[KVEventsConfig]:
     """Create KVEventsConfig for prefix caching if needed."""
-    if dynamo_config.is_decode_worker:
+    if dynamo_config.disaggregation_mode == DisaggregationMode.DECODE:
         logger.info(
-            f"Decode worker detected (is_decode_worker={dynamo_config.is_decode_worker}): "
-            f"kv_events_config disabled (decode workers don't publish KV events)"
+            "Decode worker detected (disaggregation_mode=decode): "
+            "kv_events_config disabled (decode workers don't publish KV events)"
         )
         return None
 

components/src/dynamo/vllm/backend_args.py

@@ -3,13 +3,15 @@
 
 """Dynamo vLLM wrapper configuration ArgGroup."""
 
-from typing import Optional
+import warnings
+from typing import Optional, Union
 
 from dynamo.common.configuration.arg_group import ArgGroup
 from dynamo.common.configuration.config_base import ConfigBase
 from dynamo.common.configuration.utils import add_argument, add_negatable_bool_argument
 
 from . import __version__
+from .constants import DisaggregationMode
 
 
 class DynamoVllmArgGroup(ArgGroup):
@@ -25,12 +27,23 @@ class DynamoVllmArgGroup(ArgGroup):
         )
         g = parser.add_argument_group("Dynamo vLLM Options")
 
+        add_argument(
+            g,
+            flag_name="--disaggregation-mode",
+            env_var="DYN_VLLM_DISAGGREGATION_MODE",
+            default=None,
+            help="Worker disaggregation mode: 'agg' (default, aggregated), "
+            "'prefill' (prefill-only worker), or 'decode' (decode-only worker).",
+            choices=[m.value for m in DisaggregationMode],
+        )
+
         add_negatable_bool_argument(
             g,
             flag_name="--is-prefill-worker",
             env_var="DYN_VLLM_IS_PREFILL_WORKER",
             default=False,
-            help="Enable prefill functionality for this worker. Uses the provided namespace to construct dyn://namespace.prefill.generate",
+            help="DEPRECATED: use --disaggregation-mode=prefill. "
+            "Enable prefill functionality for this worker.",
         )
 
         add_negatable_bool_argument(
@@ -38,7 +51,8 @@ class DynamoVllmArgGroup(ArgGroup):
             flag_name="--is-decode-worker",
             env_var="DYN_VLLM_IS_DECODE_WORKER",
             default=False,
-            help="Mark this as a decode worker which does not publish KV events",
+            help="DEPRECATED: use --disaggregation-mode=decode. "
+            "Mark this as a decode worker which does not publish KV events.",
         )
 
         add_negatable_bool_argument(
@@ -295,6 +309,9 @@ class DynamoVllmArgGroup(ArgGroup):
 class DynamoVllmConfig(ConfigBase):
     """Configuration for Dynamo vLLM wrapper (vLLM-specific only). All fields optional."""
 
+    disaggregation_mode: Union[
+        None, str, DisaggregationMode
+    ]  # None when not provided; resolved to enum in validate()
     is_prefill_worker: bool
     is_decode_worker: bool
     use_vllm_tokenizer: bool
@@ -344,17 +361,63 @@ class DynamoVllmConfig(ConfigBase):
 
     def validate(self) -> None:
         """Validate vLLM wrapper configuration."""
-        self._validate_prefill_decode_exclusive()
+        self._resolve_disaggregation_mode()
         self._validate_multimodal_role_exclusivity()
         self._validate_multimodal_requires_flag()
         self._validate_omni_stage_config()
 
-    def _validate_prefill_decode_exclusive(self) -> None:
-        """Ensure at most one of is_prefill_worker and is_decode_worker is set."""
+    def _resolve_disaggregation_mode(self) -> None:
+        """Resolve disaggregation_mode from new enum or legacy boolean flags.
+
+        Priority:
+        1. If --disaggregation-mode was explicitly provided, use it.
+           Raise if legacy booleans are also set.
+        2. If legacy --is-prefill-worker or --is-decode-worker is set,
+           emit DeprecationWarning and translate to enum.
+        3. Apply default (AGGREGATED) if nothing was provided.
+        4. Sync boolean fields from the resolved enum value.
+        """
+        # Convert string to enum (non-None means explicitly provided)
+        explicit_mode = self.disaggregation_mode is not None
+        if isinstance(self.disaggregation_mode, str):
+            self.disaggregation_mode = DisaggregationMode(self.disaggregation_mode)
+
+        # Check for legacy boolean flags
+        has_legacy = self.is_prefill_worker or self.is_decode_worker
+
+        if has_legacy and explicit_mode:
+            raise ValueError(
+                "Cannot combine --is-prefill-worker/--is-decode-worker with "
+                "--disaggregation-mode. Use only --disaggregation-mode."
+            )
+
+        if has_legacy:
             if self.is_prefill_worker and self.is_decode_worker:
                 raise ValueError(
                     "Cannot set both --is-prefill-worker and --is-decode-worker"
                 )
+            if self.is_prefill_worker:
+                warnings.warn(
+                    "--is-prefill-worker is deprecated, use --disaggregation-mode=prefill",
+                    DeprecationWarning,
+                    stacklevel=2,
+                )
+                self.disaggregation_mode = DisaggregationMode.PREFILL
+            elif self.is_decode_worker:
+                warnings.warn(
+                    "--is-decode-worker is deprecated, use --disaggregation-mode=decode",
+                    DeprecationWarning,
+                    stacklevel=2,
+                )
+                self.disaggregation_mode = DisaggregationMode.DECODE
+
+        # Apply default if neither new flag nor legacy flags were provided
+        if self.disaggregation_mode is None:
+            self.disaggregation_mode = DisaggregationMode.AGGREGATED
+
+        # Sync booleans from enum (canonical source of truth)
+        self.is_prefill_worker = self.disaggregation_mode == DisaggregationMode.PREFILL
+        self.is_decode_worker = self.disaggregation_mode == DisaggregationMode.DECODE
 
     def _count_multimodal_roles(self) -> int:
         """Return the number of multimodal worker roles set (0 or 1 allowed).

components/src/dynamo/vllm/constants.py

+# SPDX-FileCopyrightText: Copyright (c) 2025-2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
+# SPDX-License-Identifier: Apache-2.0
+
+"""Constants for vLLM backend.
+
+DisaggregationMode is defined in dynamo.common.constants and re-exported here
+so that existing imports from dynamo.vllm.constants continue to work.
+"""
+
+from dynamo.common.constants import DisaggregationMode
+
+__all__ = ["DisaggregationMode"]

components/src/dynamo/vllm/main.py

@@ -54,6 +54,7 @@ from dynamo.vllm.worker_factory import WorkerFactory
 
 from .args import Config, parse_args
 from .checkpoint_restore import get_checkpoint_config
+from .constants import DisaggregationMode
 from .handlers import DecodeWorkerHandler, PrefillWorkerHandler
 from .health_check import (
     VllmHealthCheckPayload,
@@ -190,7 +191,7 @@ async def worker():
     elif config.omni:
         await init_omni(runtime, config, shutdown_event)
         logger.debug("init_omni completed")
-    elif config.is_prefill_worker:
+    elif config.disaggregation_mode == DisaggregationMode.PREFILL:
         await init_prefill(
             runtime, config, shutdown_event, pre_created_engine=pre_created_engine
         )
@@ -318,7 +319,7 @@ def setup_kv_event_publisher(
         return None
 
     # Skip KV event publishing for decode workers
-    if config.is_decode_worker:
+    if config.disaggregation_mode == DisaggregationMode.DECODE:
         logger.info("Skipping KV event publisher setup for decode worker")
         return None
 
@@ -516,7 +517,8 @@ async def register_vllm_model(
     runtime_config.max_num_batched_tokens = runtime_values["max_num_batched_tokens"]
     # Decode workers don't create the WorkerKvQuery endpoint, so don't advertise local indexer
     runtime_config.enable_local_indexer = (
-        config.enable_local_indexer and not config.is_decode_worker
+        config.enable_local_indexer
+        and config.disaggregation_mode != DisaggregationMode.DECODE
     )
 
     # Add tool/reasoning parsers for decode models

components/src/dynamo/vllm/multimodal_handlers/multimodal_pd_worker_handler.py

@@ -23,6 +23,7 @@ from dynamo.common.multimodal.embedding_transfer import (
 from dynamo.runtime import Client, DistributedRuntime
 
 from ..args import Config
+from ..constants import DisaggregationMode
 from ..handlers import BaseWorkerHandler, build_sampling_params
 from ..multimodal_utils import (
     MyRequestOutput,
@@ -70,7 +71,7 @@ class MultimodalPDWorkerHandler(BaseWorkerHandler):
         self.config = config
         self.encode_worker_client = encode_worker_client
         self.decode_worker_client = decode_worker_client
-        self.enable_disagg = config.is_prefill_worker
+        self.enable_disagg = config.disaggregation_mode == DisaggregationMode.PREFILL
         self.embedding_cache_manager: MultimodalEmbeddingCacheManager | None = None
         if config.multimodal_embedding_cache_capacity_gb > 0:
             capacity_bytes = int(

components/src/dynamo/vllm/multimodal_handlers/worker_handler.py

@@ -9,6 +9,7 @@ import dynamo.nixl_connect as connect
 from dynamo.runtime import DistributedRuntime
 
 from ..args import Config
+from ..constants import DisaggregationMode
 from ..handlers import BaseWorkerHandler
 from ..multimodal_utils import MyRequestOutput, vLLMMultimodalRequest
 from ..multimodal_utils.model import construct_qwen_decode_mm_data, is_qwen_vl_model
@@ -44,7 +45,7 @@ class MultimodalDecodeWorkerHandler(BaseWorkerHandler):
         )
 
         self.config = config
-        self.enable_disagg = config.is_prefill_worker
+        self.enable_disagg = config.disaggregation_mode == DisaggregationMode.PREFILL
 
     async def async_init(self, runtime: DistributedRuntime):
         """Async initialization - connector needs async setup"""

components/src/dynamo/vllm/tests/multimodal_handlers/test_vllm_multimodal_pd_worker_handler.py

@@ -38,9 +38,16 @@ def _make_config(
     multimodal_embedding_cache_capacity_gb: float = 0,
 ) -> MagicMock:
     """Create a mock Config with the fields used by MultimodalPDWorkerHandler."""
+    from dynamo.vllm.constants import DisaggregationMode
+
     config = MagicMock()
     config.model = model
     config.is_prefill_worker = is_prefill_worker
+    config.disaggregation_mode = (
+        DisaggregationMode.PREFILL
+        if is_prefill_worker
+        else DisaggregationMode.AGGREGATED
+    )
     config.enable_multimodal = enable_multimodal
     config.multimodal_embedding_cache_capacity_gb = (
         multimodal_embedding_cache_capacity_gb

components/src/dynamo/vllm/tests/test_vllm_unit.py

@@ -4,11 +4,13 @@
 """Unit tests for vLLM backend components."""
 
 import re
+import warnings
 from pathlib import Path
 
 import pytest
 
 from dynamo.vllm.args import parse_args
+from dynamo.vllm.constants import DisaggregationMode
 from dynamo.vllm.tests.conftest import make_cli_args_fixture
 
 # Get path relative to this test file
@@ -169,13 +171,14 @@ def test_endpoint_not_provided_preserves_defaults(mock_vllm_cli):
 
 
 def test_endpoint_overrides_with_prefill_worker(mock_vllm_cli):
-    """Test that --endpoint overrides even with --is-prefill-worker."""
+    """Test that --endpoint overrides even with --disaggregation-mode prefill."""
     mock_vllm_cli(
         "--model",
         "Qwen/Qwen3-0.6B",
         "--endpoint",
         "dyn://custom.worker.serve",
-        "--is-prefill-worker",
+        "--disaggregation-mode",
+        "prefill",
     )
     config = parse_args()
     assert config.namespace == "custom"
@@ -216,3 +219,86 @@ def test_headless_namespace_has_required_fields(mock_vllm_cli):
     # Core engine fields must survive the round-trip
     assert hasattr(ns, "model")
     assert hasattr(ns, "tensor_parallel_size")
+
+
+# --disaggregation-mode tests
+
+
+def test_disaggregation_mode_default(mock_vllm_cli):
+    """Test that default disaggregation mode is AGGREGATED."""
+    mock_vllm_cli("--model", "Qwen/Qwen3-0.6B")
+    config = parse_args()
+    assert config.disaggregation_mode == DisaggregationMode.AGGREGATED
+    assert config.is_prefill_worker is False
+    assert config.is_decode_worker is False
+
+
+def test_disaggregation_mode_prefill(mock_vllm_cli):
+    """Test --disaggregation-mode prefill sets correct state."""
+    mock_vllm_cli("--model", "Qwen/Qwen3-0.6B", "--disaggregation-mode", "prefill")
+    config = parse_args()
+    assert config.disaggregation_mode == DisaggregationMode.PREFILL
+    assert config.is_prefill_worker is True
+    assert config.is_decode_worker is False
+    assert config.component == "prefill"
+
+
+def test_disaggregation_mode_decode(mock_vllm_cli):
+    """Test --disaggregation-mode decode sets correct state."""
+    mock_vllm_cli("--model", "Qwen/Qwen3-0.6B", "--disaggregation-mode", "decode")
+    config = parse_args()
+    assert config.disaggregation_mode == DisaggregationMode.DECODE
+    assert config.is_prefill_worker is False
+    assert config.is_decode_worker is True
+
+
+def test_legacy_is_prefill_worker_emits_deprecation(mock_vllm_cli):
+    """Test that --is-prefill-worker still works but emits DeprecationWarning."""
+    mock_vllm_cli("--model", "Qwen/Qwen3-0.6B", "--is-prefill-worker")
+    with warnings.catch_warnings(record=True) as w:
+        warnings.simplefilter("always")
+        config = parse_args()
+    deprecation_warnings = [x for x in w if issubclass(x.category, DeprecationWarning)]
+    assert len(deprecation_warnings) >= 1
+    assert "deprecated" in str(deprecation_warnings[0].message).lower()
+    assert config.disaggregation_mode == DisaggregationMode.PREFILL
+    assert config.is_prefill_worker is True
+
+
+def test_legacy_is_decode_worker_emits_deprecation(mock_vllm_cli):
+    """Test that --is-decode-worker still works but emits DeprecationWarning."""
+    mock_vllm_cli("--model", "Qwen/Qwen3-0.6B", "--is-decode-worker")
+    with warnings.catch_warnings(record=True) as w:
+        warnings.simplefilter("always")
+        config = parse_args()
+    deprecation_warnings = [x for x in w if issubclass(x.category, DeprecationWarning)]
+    assert len(deprecation_warnings) >= 1
+    assert "deprecated" in str(deprecation_warnings[0].message).lower()
+    assert config.disaggregation_mode == DisaggregationMode.DECODE
+    assert config.is_decode_worker is True
+
+
+def test_conflicting_legacy_and_new_flags_raises(mock_vllm_cli):
+    """Test that combining legacy flags with explicit --disaggregation-mode raises ValueError."""
+    mock_vllm_cli(
+        "--model",
+        "Qwen/Qwen3-0.6B",
+        "--disaggregation-mode",
+        "prefill",
+        "--is-decode-worker",
+    )
+    with pytest.raises(ValueError, match="Cannot combine"):
+        parse_args()
+
+
+def test_explicit_default_mode_with_legacy_flag_raises(mock_vllm_cli):
+    """Test that --disaggregation-mode agg --is-decode-worker raises ValueError."""
+    mock_vllm_cli(
+        "--model",
+        "Qwen/Qwen3-0.6B",
+        "--disaggregation-mode",
+        "agg",
+        "--is-decode-worker",
+    )
+    with pytest.raises(ValueError, match="Cannot combine"):
+        parse_args()

components/src/dynamo/vllm/worker_factory.py

@@ -13,6 +13,7 @@ from dynamo.llm import ModelInput
 from dynamo.runtime import DistributedRuntime
 
 from .args import Config
+from .constants import DisaggregationMode
 from .multimodal_handlers import (
     EncodeWorkerHandler,
     MultimodalDecodeWorkerHandler,
@@ -149,7 +150,7 @@ class WorkerFactory:
 
         # Set up decode worker client for disaggregated mode
         decode_worker_client = None
-        if config.is_prefill_worker:
+        if config.disaggregation_mode == DisaggregationMode.PREFILL:
             decode_worker_client = await runtime.endpoint(
                 f"{config.namespace}.decoder.generate"
             ).client()