OKiSrSSKJr SSKJr SSKJrJrJrJ r J r J r SSK J r \(aSSKJrJr SSKJr SSKJr "S S \\\ \\ 45rg ) z%Model fallback middleware for agents.) annotations) TYPE_CHECKING)AgentMiddleware AgentStateContextT ModelRequest ModelResponse ResponseT)init_chat_model) AwaitableCallable) BaseChatModel) AIMessagech^\rSrSrSrSU4SjjrSSjrS SjrSrU=r $) ModelFallbackMiddlewarea Automatic fallback to alternative models on errors. Retries failed model calls with alternative models in sequence until success or all models exhausted. Primary model specified in `create_agent`. Example: ```python from langchain.agents.middleware.model_fallback import ModelFallbackMiddleware from langchain.agents import create_agent fallback = ModelFallbackMiddleware( "openai:gpt-4o-mini", # Try first on error "anthropic:claude-sonnet-4-5-20250929", # Then this ) agent = create_agent( model="openai:gpt-4o", # Primary model middleware=[fallback], ) # If primary fails: tries gpt-4o-mini, then claude-sonnet-4-5-20250929 result = await agent.invoke({"messages": [HumanMessage("Hello")]}) ``` c>[TU]5 U/UQ7n/UlUHYn[U[5(a&URR [ U55 M>URR U5 M[ g)zInitialize model fallback middleware. Args: first_model: First fallback model (string name or instance). *additional_models: Additional fallbacks in order. N)super__init__models isinstancestrappendr )self first_modeladditional_models all_modelsmodel __class__s l/var/www/html/dynamic-report/venv/lib/python3.13/site-packages/langchain/agents/middleware/model_fallback.pyr ModelFallbackMiddleware.__init__2sg "6$56 +- E%%% ""?5#9: ""5)  cU"U5$![a nUnSnAOSnAff=fURH3nU"URUS95s $![a nUnSnAM-SnAff=f Ue)zTry fallback models in sequence on errors. Args: request: Initial model request. handler: Callback to execute the model. Returns: AIMessage from successful model call. Raises: Exception: If all models fail, re-raises last exception. Nr Exceptionroverriderrequesthandlerelast_exceptionfallback_models r wrap_model_call'ModelFallbackMiddleware.wrap_model_callHsu& 7# # N #kkN w//n/EFF !" *s'  A  A!AA!c# U"U5IShvN $N![a nUnSnAOSnAff=fURH<nU"URUS95IShvN s $![a nUnSnAM6SnAff=f Ue7f)aTry fallback models in sequence on errors (async version). Args: request: Initial model request. handler: Async callback to execute the model. Returns: AIMessage from successful model call. Raises: Exception: If all models fail, re-raises last exception. Nr$r%r(s r awrap_model_call(ModelFallbackMiddleware.awrap_model_calljs&  )) )) N #kkN $W%5%5N%5%KLLLL !" *seA= A= ,'A=,A=AAAA= A6)A1+A=1A66A=)r)rstr | BaseChatModelrr3returnNone)r)ModelRequest[ContextT]r*zrGsH+" 23H1roj.CXy.XYrr"