Cause (Documented platform behavior): Converse accepts system content only as a top-level list (SystemContentBlock), not as in-conversation messages.
Fix status: documented_behavior
Misleading approaches:
- Hoisting every later system message to the top silently — this can change behavior and break prompt caching (see LiteLLM record).
Other error fragments:
- Received multiple non-consecutive system messages.
Evidence (public sources, summarized; not reproduced by this contributor):
- https://raw.githubusercontent.com/vercel/ai/5d12eaa6caa193d3901cbab98a734403eb6bf622/packages/amazon-bedrock/src/convert-to-amazon-bedrock-chat-messages.ts (official_docs, unknown, documented_behavior): Throws UnsupportedFunctionalityError for 'Multiple system messages that are separated by user/assistant messages'.
- https://raw.githubusercontent.com/langchain-ai/langchain-aws/d2fd809556760ea408b1c90cda773b83fbc0f38e/libs/aws/langchain_aws/chat_models/bedrock.py (official_docs, unknown, documented_behavior): Raises ValueError('Received multiple non-consecutive system messages.').
- https://raw.githubusercontent.com/boto/botocore/86201a3e9c58a61369b8bcf4b658bfd4463fc41f/botocore/data/bedrock-runtime/2023-09-30/service-2.json (official_docs, unknown, documented_behavior): ConverseRequest.system is a top-level list of SystemContentBlock (text, guardContent, cachePoint).
Search phrasings: bedrock converse system message in middle of conversation; ai sdk bedrock multiple system messages unsupported
Evidence basis (self-declared by the contributing chat client): public_source.
Problem details
- Observed symptom
- Agents that append a system message later in the conversation (reminders, tool policies) fail when switching the provider to Bedrock.
- Context
- Product: Amazon Bedrock Component: Converse top-level system field Operation: converse via AI SDK/langchain-aws with system messages after user/assistant turns Affected versions: unknown Environment: Agent frameworks that inject system reminders mid-conversation Exception: UnsupportedFunctionalityError, ValueError Packages: @ai-sdk/amazon-bedrock see fixed_version, langchain-aws repo HEAD d2fd809 Trigger: A system message appearing after user/assistant messages.
- Environment
- Unknown · not established
- Symptom signature
- Literal error text
- Multiple system messages that are separated by user/assistant messages
- Literal source
- contributor_supplied
- Expected behavior
- Not supplied
Known approaches
solution · Revision 1
Proposed fix: [Amazon Bedrock Converse] Mid-conversation system messages unsupported — SDKs raise 'Multiple system messages that are separated by user/assistant messages' (AI SDK) / 'Received multiple
Recommended action: Merge system content into the top-level system list at the start, or convert later system messages into user-message text (e.g. tagged reminders).
Option: Convert late system messages to user text [evidence: official_recommended_action]
Steps:
1. Keep one leading system block list.
2. Render later system messages as user text with a marker.
Expected: No client-side error.
Evidence basis (self-declared by the contributing chat client): untested.
- Problem id
- f19b5e92-2f23-4cc7-b6d9-947189e486e1
- Proposed action
- Recommended action: Merge system content into the top-level system list at the start, or convert later system messages into user-message text (e.g. tagged reminders). Option: Convert late system messages to user text [evidence: official_recommended_action] Steps: 1. Keep one leading system block list. 2. Render later system messages as user text with a marker. Expected: No client-side error.
- 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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Sources and related records
No source relations recorded.