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strands.types.event_loop

Event loop-related type definitions for the SDK.

StopReason = Literal['content_filtered', 'end_turn', 'guardrail_intervened', 'interrupt', 'max_tokens', 'stop_sequence', 'tool_use'] module-attribute

Reason for the model ending its response generation.

  • "content_filtered": Content was filtered due to policy violation
  • "end_turn": Normal completion of the response
  • "guardrail_intervened": Guardrail system intervened
  • "interrupt": Agent was interrupted for human input
  • "max_tokens": Maximum token limit reached
  • "stop_sequence": Stop sequence encountered
  • "tool_use": Model requested to use a tool

Metrics

Bases: TypedDict

Performance metrics for model interactions.

Attributes:

Name Type Description
latencyMs int

Latency of the model request in milliseconds.
timeToFirstByteMs int

Latency from sending model request to first content chunk (contentBlockDelta or contentBlockStart) from the model in milliseconds.
Source code in strands/types/event_loop.py 
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class Metrics(TypedDict, total=False):
    """Performance metrics for model interactions.

    Attributes:
        latencyMs (int): Latency of the model request in milliseconds.
        timeToFirstByteMs (int): Latency from sending model request to first
            content chunk (contentBlockDelta or contentBlockStart) from the model in milliseconds.
    """

    latencyMs: Required[int]
    timeToFirstByteMs: int

Usage

Bases: TypedDict

Token usage information for model interactions.

Attributes:

Name Type Description
inputTokens Required[int]

Number of tokens sent in the request to the model.
outputTokens Required[int]

Number of tokens that the model generated for the request.
totalTokens Required[int]

Total number of tokens (input + output).
cacheReadInputTokens int

Number of tokens read from cache (optional).
cacheWriteInputTokens int

Number of tokens written to cache (optional).
Source code in strands/types/event_loop.py 
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class Usage(TypedDict, total=False):
    """Token usage information for model interactions.

    Attributes:
        inputTokens: Number of tokens sent in the request to the model.
        outputTokens: Number of tokens that the model generated for the request.
        totalTokens: Total number of tokens (input + output).
        cacheReadInputTokens: Number of tokens read from cache (optional).
        cacheWriteInputTokens: Number of tokens written to cache (optional).
    """

    inputTokens: Required[int]
    outputTokens: Required[int]
    totalTokens: Required[int]
    cacheReadInputTokens: int
    cacheWriteInputTokens: int