AsyncRedisSaver Serialization TypeError

[RobCaamano]

AsyncRedisSaver raises TypeError: Object of type HumanMessage is not JSON serializable during checkpoint writes

Hello!

• This is a bug, not a usage question.

Environment

• Python: 3.12.3
• langgraph: 1.1.2
• langgraph-checkpoint: 4.0.1
• langgraph-checkpoint-redis: 0.4.0
• redisvl: 0.16.0
• Redis: Redis 8.6.1 Stack (RedisJSON + RediSearch enabled)

Bug Description

When using AsyncRedisSaver as the checkpointer for a graph whose state includes a messages channel with LangChain message objects (HumanMessage, AIMessage), checkpoint writes fail with:

TypeError: Object of type HumanMessage is not JSON serializable

The error originates inside redisvl's storage layer during client.json().set(), meaning the message objects are reaching RedisJSON without being serialized through JsonPlusRedisSerializer first.

Key observations:

• Removing checkpointer=checkpointer from graph.compile() eliminates the error entirely.
• The same graph works correctly with InMemorySaver, confirming the graph logic and state shape are valid.

Full Traceback

ERROR:redisvl.index.index:Error while loading data to Redis
Traceback (most recent call last):
  File ".../redisvl/index/index.py", line 1833, in load
    return await self._storage.awrite(
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".../redisvl/index/storage.py", line 503, in awrite
    await self._aset(pipe, key, obj)
  File ".../redisvl/index/storage.py", line 705, in _aset
    client.json().set(key, "$", obj)
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".../redis/commands/json/commands.py", line 243, in set
    pieces = [name, str(path), self._encode(obj)]
                                ^^^^^^^^^^^^^^^^^
  File ".../redis/commands/json/__init__.py", line 102, in _encode
    return self.__encoder__.encode(obj)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.12/json/encoder.py", line 200, in encode
    chunks = self.iterencode(o, _one_shot=True)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.12/json/encoder.py", line 258, in iterencode
    return _iterencode(o, 0)
           ^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.12/json/encoder.py", line 180, in default
    raise TypeError(f'Object of type {o.__class__.__name__} '
TypeError: Object of type HumanMessage is not JSON serializable

Expected Behavior

AsyncRedisSaver should serialize HumanMessage and AIMessage objects in all checkpoint paths (channel values, pending writes, pending sends, and metadata) using JsonPlusRedisSerializer, the same way the first-party AsyncPostgresSaver and InMemorySaver handle them via JsonPlusSerializer.

Thanks for looking into this!