refactor: replace Any-typed callback and model fields with serializable types

lib/crewai/src/crewai/agent/core.py

@@ -66,6 +66,7 @@ from crewai.mcp.tool_resolver import MCPToolResolver
 from crewai.rag.embeddings.types import EmbedderConfig
 from crewai.security.fingerprint import Fingerprint
 from crewai.tools.agent_tools.agent_tools import AgentTools
+from crewai.types.callback import SerializableCallable
 from crewai.utilities.agent_utils import (
     get_tool_names,
     is_inside_event_loop,
@@ -143,7 +144,7 @@ class Agent(BaseAgent):
         default=None,
         description="Maximum execution time for an agent to execute a task",
     )
-    step_callback: Any | None = Field(
+    step_callback: SerializableCallable | None = Field(
         default=None,
         description="Callback to be executed after each step of the agent execution.",
     )
@@ -151,10 +152,10 @@ class Agent(BaseAgent):
         default=True,
         description="Use system prompt for the agent.",
     )
-    llm: str | InstanceOf[BaseLLM] | Any = Field(
+    llm: str | InstanceOf[BaseLLM] | None = Field(
         description="Language model that will run the agent.", default=None
     )
-    function_calling_llm: str | InstanceOf[BaseLLM] | Any | None = Field(
+    function_calling_llm: str | InstanceOf[BaseLLM] | None = Field(
         description="Language model that will run the agent.", default=None
     )
     system_template: str | None = Field(
@@ -340,7 +341,7 @@ class Agent(BaseAgent):
         return (
             hasattr(self.llm, "supports_function_calling")
             and callable(getattr(self.llm, "supports_function_calling", None))
-            and self.llm.supports_function_calling()
+            and self.llm.supports_function_calling()  # type: ignore[union-attr]
             and len(tools) > 0
         )
 

lib/crewai/src/crewai/agents/agent_builder/base_agent.py

@@ -12,6 +12,7 @@ from pydantic import (
     UUID4,
     BaseModel,
     Field,
+    InstanceOf,
     PrivateAttr,
     field_validator,
     model_validator,
@@ -26,7 +27,10 @@ from crewai.agents.tools_handler import ToolsHandler
 from crewai.knowledge.knowledge import Knowledge
 from crewai.knowledge.knowledge_config import KnowledgeConfig
 from crewai.knowledge.source.base_knowledge_source import BaseKnowledgeSource
+from crewai.knowledge.storage.base_knowledge_storage import BaseKnowledgeStorage
 from crewai.mcp.config import MCPServerConfig
+from crewai.memory.memory_scope import MemoryScope, MemorySlice
+from crewai.memory.unified_memory import Memory
 from crewai.rag.embeddings.types import EmbedderConfig
 from crewai.security.security_config import SecurityConfig
 from crewai.tools.base_tool import BaseTool, Tool
@@ -179,7 +183,7 @@ class BaseAgent(BaseModel, ABC, metaclass=AgentMeta):
         default=None,
         description="Knowledge sources for the agent.",
     )
-    knowledge_storage: Any | None = Field(
+    knowledge_storage: InstanceOf[BaseKnowledgeStorage] | None = Field(
         default=None,
         description="Custom knowledge storage for the agent.",
     )
@@ -205,7 +209,7 @@ class BaseAgent(BaseModel, ABC, metaclass=AgentMeta):
         default=None,
         description="List of MCP server references. Supports 'https://server.com/path' for external servers and bare slugs like 'notion' for connected MCP integrations. Use '#tool_name' suffix for specific tools.",
     )
-    memory: Any = Field(
+    memory: bool | Memory | MemoryScope | MemorySlice | None = Field(
         default=None,
         description=(
             "Enable agent memory. Pass True for default Memory(), "

lib/crewai/src/crewai/crew.py

@@ -35,6 +35,7 @@ from typing_extensions import Self
 
 if TYPE_CHECKING:
     from crewai_files import FileInput
+    from opentelemetry.trace import Span
 
 try:
     from crewai_files import get_supported_content_types
@@ -83,6 +84,8 @@ from crewai.knowledge.knowledge import Knowledge
 from crewai.knowledge.source.base_knowledge_source import BaseKnowledgeSource
 from crewai.llm import LLM
 from crewai.llms.base_llm import BaseLLM
+from crewai.memory.memory_scope import MemoryScope, MemorySlice
+from crewai.memory.unified_memory import Memory
 from crewai.process import Process
 from crewai.rag.embeddings.types import EmbedderConfig
 from crewai.rag.types import SearchResult
@@ -94,6 +97,7 @@ from crewai.tasks.task_output import TaskOutput
 from crewai.tools.agent_tools.agent_tools import AgentTools
 from crewai.tools.agent_tools.read_file_tool import ReadFileTool
 from crewai.tools.base_tool import BaseTool
+from crewai.types.callback import SerializableCallable
 from crewai.types.streaming import CrewStreamingOutput
 from crewai.types.usage_metrics import UsageMetrics
 from crewai.utilities.constants import NOT_SPECIFIED, TRAINING_DATA_FILE
@@ -166,12 +170,12 @@ class Crew(FlowTrackable, BaseModel):
     """
 
     __hash__ = object.__hash__
-    _execution_span: Any = PrivateAttr()
+    _execution_span: Span | None = PrivateAttr()
     _rpm_controller: RPMController = PrivateAttr()
     _logger: Logger = PrivateAttr()
     _file_handler: FileHandler = PrivateAttr()
     _cache_handler: InstanceOf[CacheHandler] = PrivateAttr(default_factory=CacheHandler)
-    _memory: Any = PrivateAttr(default=None)  # Unified Memory | MemoryScope
+    _memory: Memory | MemoryScope | MemorySlice | None = PrivateAttr(default=None)
     _train: bool | None = PrivateAttr(default=False)
     _train_iteration: int | None = PrivateAttr()
     _inputs: dict[str, Any] | None = PrivateAttr(default=None)
@@ -189,7 +193,7 @@ class Crew(FlowTrackable, BaseModel):
     agents: list[BaseAgent] = Field(default_factory=list)
     process: Process = Field(default=Process.sequential)
     verbose: bool = Field(default=False)
-    memory: bool | Any = Field(
+    memory: bool | Memory | MemoryScope | MemorySlice | None = Field(
         default=False,
         description=(
             "Enable crew memory. Pass True for default Memory(), "
@@ -204,23 +208,23 @@ class Crew(FlowTrackable, BaseModel):
         default=None,
         description="Metrics for the LLM usage during all tasks execution.",
     )
-    manager_llm: str | InstanceOf[BaseLLM] | Any | None = Field(
+    manager_llm: str | InstanceOf[BaseLLM] | None = Field(
         description="Language model that will run the agent.", default=None
     )
     manager_agent: BaseAgent | None = Field(
         description="Custom agent that will be used as manager.", default=None
     )
-    function_calling_llm: str | InstanceOf[LLM] | Any | None = Field(
+    function_calling_llm: str | InstanceOf[LLM] | None = Field(
         description="Language model that will run the agent.", default=None
     )
     config: Json[dict[str, Any]] | dict[str, Any] | None = Field(default=None)
     id: UUID4 = Field(default_factory=uuid.uuid4, frozen=True)
     share_crew: bool | None = Field(default=False)
-    step_callback: Any | None = Field(
+    step_callback: SerializableCallable | None = Field(
         default=None,
         description="Callback to be executed after each step for all agents execution.",
     )
-    task_callback: Any | None = Field(
+    task_callback: SerializableCallable | None = Field(
         default=None,
         description="Callback to be executed after each task for all agents execution.",
     )
@@ -349,7 +353,7 @@ class Crew(FlowTrackable, BaseModel):
             self._file_handler = FileHandler(self.output_log_file)
         self._rpm_controller = RPMController(max_rpm=self.max_rpm, logger=self._logger)
         if self.function_calling_llm and not isinstance(self.function_calling_llm, LLM):
-            self.function_calling_llm = create_llm(self.function_calling_llm)
+            self.function_calling_llm = create_llm(self.function_calling_llm)  # type: ignore[assignment]
 
         return self
 
@@ -363,7 +367,7 @@ class Crew(FlowTrackable, BaseModel):
             if self.embedder is not None:
                 from crewai.rag.embeddings.factory import build_embedder
 
-                embedder = build_embedder(self.embedder)
+                embedder = build_embedder(self.embedder)  # type: ignore[arg-type]
             self._memory = Memory(embedder=embedder)
         elif self.memory:
             # User passed a Memory / MemoryScope / MemorySlice instance

lib/crewai/src/crewai/memory/unified_memory.py

@@ -22,7 +22,6 @@ from crewai.events.types.memory_events import (
 )
 from crewai.llms.base_llm import BaseLLM
 from crewai.memory.analyze import extract_memories_from_content
-from crewai.memory.recall_flow import RecallFlow
 from crewai.memory.storage.backend import StorageBackend
 from crewai.memory.types import (
     MemoryConfig,
@@ -620,6 +619,8 @@ class Memory(BaseModel):
                         )
                     results.sort(key=lambda m: m.score, reverse=True)
             else:
+                from crewai.memory.recall_flow import RecallFlow
+
                 flow = RecallFlow(
                     storage=self._storage,
                     llm=self._llm,

lib/crewai/src/crewai/task.py

@@ -67,6 +67,7 @@ except ImportError:
         return []
 
 
+from crewai.types.callback import SerializableCallable
 from crewai.utilities.guardrail import (
     process_guardrail,
 )
@@ -124,7 +125,7 @@ class Task(BaseModel):
         description="Configuration for the agent",
         default=None,
     )
-    callback: Any | None = Field(
+    callback: SerializableCallable | None = Field(
         description="Callback to be executed after the task is completed.", default=None
     )
     agent: BaseAgent | None = Field(

lib/crewai/src/crewai/types/callback.py

@@ -0,0 +1,90 @@
+"""Serializable callback type for Pydantic models.
+
+Provides a ``SerializableCallable`` type alias that enables full JSON
+round-tripping of callback fields, e.g. ``"builtins.print"`` ↔ ``print``.
+Lambdas and closures serialize to a dotted path but cannot be deserialized
+back — use module-level named functions for checkpointable callbacks.
+"""
+
+from __future__ import annotations
+
+from collections.abc import Callable
+import importlib
+import inspect
+from typing import Annotated, Any
+import warnings
+
+from pydantic import BeforeValidator, WithJsonSchema
+from pydantic.functional_serializers import PlainSerializer
+
+
+def _is_lambda(fn: object) -> bool:
+    """Return ``True`` if *fn* is a lambda expression.
+
+    Uses ``__qualname__`` ending with ``"<lambda>"`` for resilience against
+    ``__name__`` being reassigned.  ``inspect.isfunction`` gates the check
+    so non-function callables (classes, partials, etc.) are never flagged.
+
+    Args:
+        fn: The object to check.
+
+    Returns:
+        ``True`` if *fn* is a lambda, ``False`` otherwise.
+    """
+    return inspect.isfunction(fn) and getattr(fn, "__qualname__", "").endswith(
+        "<lambda>"
+    )
+
+
+def string_to_callable(value: Any) -> Callable[..., Any]:
+    """Convert a dotted path string to the callable it references.
+
+    If *value* is already callable it is returned as-is, with a warning if
+    it is a lambda.  Otherwise, it is treated as ``"module.qualname"`` and
+    resolved via :func:`importlib.import_module`.
+
+    Args:
+        value: A callable or a dotted-path string e.g. ``"builtins.print"``.
+
+    Returns:
+        The resolved callable.
+
+    Raises:
+        ModuleNotFoundError: If the module portion of the path cannot be imported.
+        AttributeError: If the attribute cannot be found on the imported module.
+    """
+    if callable(value):
+        if _is_lambda(value):
+            warnings.warn(
+                "Lambdas cannot be serialized and will prevent checkpointing. "
+                "Use a module-level named function instead.",
+                UserWarning,
+                stacklevel=2,
+            )
+        return value  # type: ignore[no-any-return]
+    module, func = value.rsplit(".", 1)
+    return getattr(importlib.import_module(module), func)  # type: ignore[no-any-return]
+
+
+def callable_to_string(fn: Callable[..., Any]) -> str:
+    """Serialize a callable to its dotted-path string representation.
+
+    Uses ``fn.__module__`` and ``fn.__qualname__`` to produce a string such
+    as ``"builtins.print"``.  Lambdas and closures produce paths that contain
+    ``<locals>`` and cannot be round-tripped via :func:`string_to_callable`.
+
+    Args:
+        fn: The callable to serialize.
+
+    Returns:
+        A dotted string of the form ``"module.qualname"``.
+    """
+    return f"{fn.__module__}.{fn.__qualname__}"
+
+
+SerializableCallable = Annotated[
+    Callable[..., Any],
+    BeforeValidator(string_to_callable),
+    PlainSerializer(callable_to_string, return_type=str),
+    WithJsonSchema({"type": "string"}),
+]

lib/crewai/tests/agents/test_agent.py

@@ -1690,7 +1690,10 @@ def test_agent_with_knowledge_sources_works_with_copy():
         with patch(
             "crewai.knowledge.storage.knowledge_storage.KnowledgeStorage"
         ) as mock_knowledge_storage:
+            from crewai.knowledge.storage.base_knowledge_storage import BaseKnowledgeStorage
+
             mock_knowledge_storage_instance = mock_knowledge_storage.return_value
+            mock_knowledge_storage_instance.__class__ = BaseKnowledgeStorage
             agent.knowledge_storage = mock_knowledge_storage_instance
 
             agent_copy = agent.copy()