LangGraph v1 + LangChain v1 (Python): delta-only notes for writing valid v1 code

0) Version + Python floor

• •Assume Python 3.10+ (LangGraph v1 drops 3.9).
• •Upgrade baseline:
  • •pip install -U langgraph langchain-core

1) LangGraph Graph API is stable (mostly unchanged)

• •Graph API imports remain:
  • •from langgraph.graph import START, END, StateGraph

2) LangGraph Functional API exists (v1 docs-first path)

• •Entrypoints are defined via:
  • •from langgraph.func import entrypoint
• •Entrypoint function must accept one positional input argument (use a dict if multiple inputs are needed).
• •Entrypoints can request injectable params by name + type annotation:
  • •previous, store, writer, config
• •Common v1 import paths shown in docs/examples:
  • •from langgraph.store.base import BaseStore
  • •from langgraph.store.memory import InMemoryStore
  • •from langgraph.checkpoint.memory import InMemorySaver

3) Checkpointing / persistence packages and imports

• •In-memory checkpointer:
  • •from langgraph.checkpoint.memory import InMemorySaver
• •SQLite/Postgres checkpointers are separate installables:
  • •langgraph-checkpoint-sqlite (SqliteSaver / AsyncSqliteSaver)
  • •langgraph-checkpoint-postgres (PostgresSaver / AsyncPostgresSaver)
• •(If using custom serialization) serde lives under:
  • •langgraph.checkpoint.serde.*

4) LangGraph v1 deprecations (replace these)

LangGraph v1 is backwards compatible overall, but deprecates specific agent/runtime helpers:

4.1) MessageGraph (deprecated) → StateGraph + messages key

• •Replace MessageGraph usage with StateGraph and a state that contains a messages key.

4.2) ValidationNode (deprecated)

• •If you were using langgraph.prebuilt.ValidationNode, prefer LangChain v1 create_agent tool validation + middleware error handling (see section 5).

4.3) Agent prebuilt + agent state moved out of LangGraph

• •Deprecated in LangGraph v1:
  • •langgraph.prebuilt.create_react_agent
  • •langgraph.prebuilt.AgentState and pydantic variants
  • •LangGraph interrupt TypedDicts (HumanInterruptConfig / ActionRequest / HumanInterrupt)
• •Replacements live in LangChain v1:
  • •from langchain.agents import create_agent
  • •from langchain.agents import AgentState
  • •interrupt types: from langchain.agents.interrupt import HumanInterruptConfig, ActionRequest, HumanInterrupt

5) LangChain v1 agent API (built on LangGraph)

If you’re building an “agent loop” via prebuilts, v1 expects LangChain’s API:

5.1) create_react_agent → create_agent

• •Replace:
  • •from langgraph.prebuilt import create_react_agent
• •With:
  • •from langchain.agents import create_agent

5.2) prompt → system_prompt (string)

• •system_prompt="..." (string), not SystemMessage.

5.3) Hooks → middleware

• •pre_model_hook/post_model_hook patterns move to middleware (before_model/after_model).

5.4) Tools: pass a list, not a ToolNode

• •create_agent(..., tools=[...])
• •Do not wrap tools in ToolNode(...) for create_agent.

5.5) State schemas: TypedDict-only

• •create_agent(..., state_schema=SomeTypedDict)
• •No pydantic/dataclass state schemas.

5.6) Streaming node name

• •When streaming agent events, the node name is "model" (not "agent").

6) Key “don’t break imports” reminders

• •Graph API: langgraph.graph (START/END/StateGraph)
• •Functional API: langgraph.func (entrypoint)
• •Checkpointing: langgraph.checkpoint.* (InMemorySaver, sqlite/postgres modules)
• •Store/memory: langgraph.store.*
• •Agent prebuilt migration target: langchain.agents (create_agent, AgentState) and langchain.agents.interrupt (interrupt types)