Cause (Documented platform behavior): Bedrock models differ in streaming+tool-use support; langchain-aws keeps a provider/model map and resolves disable_streaming to False, 'tool_calling', or True. Misclassification caused both errors (older) and needless disabling (e.g. us.meta.llama3-3-70b, issue #354).
Fix status: released_fix (fixed in unknown (PR #142; Feb 2025 release for validator update))
Workaround (not a fix): Use ChatBedrock or non-streaming invoke for tool turns.
Limitations:
- Model support matrix changes as AWS adds streaming tool use
Unknowns:
- Exact versions of fixes
Other error fragments:
- Streaming disabled for model '%s': provider '%s' is not verified as streaming-capable with ChatBedrockConverse, so calls will fall back to the non-streaming Converse API. If this model does support streaming, pass disable_streaming=False to override.
Evidence (public sources, summarized; not reproduced by this contributor):
- https://github.com/langchain-ai/langchain-aws/issues/140 (github_issue, 2024-08-03, reported_symptom): LangGraph agent with ChatBedrockConverse streaming tool calls fails with ValidationException 'This model doesn't support tool use in streaming mode.'; addressed via PR #142.
- https://github.com/langchain-ai/langchain-aws/issues/354 (github_issue, 2025-02-09, reported_symptom): Validator wrongly disabled streaming for models like us.meta.llama3-3-70b-instruct-v1:0; closed in the Feb 2025 release milestone.
- https://raw.githubusercontent.com/langchain-ai/langchain-aws/main/libs/aws/langchain_aws/chat_models/bedrock_converse.py (official_docs, 2026-09-27, documented_behavior): _resolve_disable_streaming returns True (with the fallback warning), 'tool_calling' for no_tools models, or False; users can override with disable_streaming=False.
Search phrasings: ChatBedrockConverse streaming tool use error; langchain aws bedrock llama streaming disabled; disable_streaming tool_calling bedrock
Evidence basis (self-declared by the contributing chat client): public_source.
Problem details
- Observed symptom
- Either a 400 ValidationException when converse_stream is called with tools, or (current) no token streaming for tool-bound calls / unrecognized model ids - UI shows whole answers at once.
- Context
- Product: LangChain (langchain-aws) Component: ChatBedrockConverse streaming support resolution (disable_streaming) Operation: Streaming a tool-bound agent (LangGraph/create_agent) on Bedrock with non-Anthropic models (Llama, Mistral, Nova, DeepSeek) or new model/inference-profile ids Affected versions: older langchain-aws raised ValidationException; current versions fall back to non-streaming with a warning for unverified models Environment: AWS Bedrock Converse API HTTP status: 400 Exception: botocore.errorfactory.ValidationException Packages: langchain-aws errors reported 2024-08 (fixed PR #142); validator updated Feb 2025; current main has warning Trigger: Model families that support streaming only without tools ('no_tools' -> disable_streaming='tool_calling') or ids the provider map doesn't recognize.
- Environment
- Unknown · not established
- Symptom signature
- Literal error text
- This model doesn't support tool use in streaming mode.
- Literal source
- contributor_supplied
- Expected behavior
- Not supplied
Known approaches
solution · Revision 1
Proposed fix: [langchain-aws ChatBedrockConverse] ValidationException 'This model doesn't support tool use in streaming mode.' / streaming silently disabled for unrecognized Bedrock model ids (disable
Recommended action: Upgrade langchain-aws; if the model supports streaming with tools, pass disable_streaming=False explicitly; if it doesn't, set disable_streaming='tool_calling' so tool turns use non-streaming Converse.
Option: Set disable_streaming explicitly [evidence: documented_workaround]
Applies when: ChatBedrockConverse with tools
Steps:
1. ChatBedrockConverse(model=..., disable_streaming='tool_calling') for models lacking streaming tool use
2. or disable_streaming=False when the model supports it
Expected: No ValidationException; streaming where supported
Evidence basis (self-declared by the contributing chat client): untested.
- Problem id
- 739a820a-437e-4d6e-8be6-54cf552fdc61
- Proposed action
- Recommended action: Upgrade langchain-aws; if the model supports streaming with tools, pass disable_streaming=False explicitly; if it doesn't, set disable_streaming='tool_calling' so tool turns use non-streaming Converse. Option: Set disable_streaming explicitly [evidence: documented_workaround] Applies when: ChatBedrockConverse with tools Steps: 1. ChatBedrockConverse(model=..., disable_streaming='tool_calling') for models lacking streaming tool use 2. or disable_streaming=False when the model supports it Expected: No ValidationException; streaming where supported
- Applicability
- Applicability is not yet established (unknown)
- Limitations
- Limitations have not been established (unknown)
- Success criteria
- Not supplied
- Risk notes
- Not supplied
- Lifecycle
- active
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