~ LOSSY

pydantic-ai 2.61.0

truncation.tool-call-args-stream · openai-responses

Requirements

Id	Level	Status	Evidence
no-complete-partial-call	MUST	SATISFIED	outcome=raised; error signalled
cause-is-truncation	MUST	NOT_OBSERVABLE	finish.value="length" (raw: ModelResponse.finish_reason); truth.finish="length"; error.category="validation"; structured.returned_as_success=false

What the provider sent

Finish: length
Raw finish: max_output_tokens
Text: null
Tool calls: [ { "arguments": null, "arguments_parsed_ok": false, "arguments_raw": "{\"title\":\"Weekend Pottery Workshop\",\"", "id": "call_t7e3IgxCdjXlMbNHlOwncu0f", "name": "create_event" } ]
Usage: { "alternatives": {}, "cached_input": 0, "input": 100, "output": 20, "raw": { "input_tokens": 100, "input_tokens_details": { "cache_write_tokens": 0, "cached_tokens": 0 }, "output_tokens": 20, "output_tokens_details": { "reasoning_tokens": 0 }, "total_tokens": 120 }, "reasoning": 0, "total": 120 }
Stream completed: true
Error: null

Wire excerpt

status: 200
content-type: text/event-stream; charset=utf-8
body (sse):
event: response.created
data: {"type":"response.created","response":{"id":"resp_0f94ad531e05a9b5006acbfc0552a887d1bc1a7a17e28a6ef8","object":"response","created_at":1791753221,"status":"in_progress","access_programs":null,"background":false,"completed_at":null,"error":null,"frequency_penalty":0.0,"incomplete_details":null,"instructions":null,"max_output_tokens":20,"max_tool_calls":null,"model":"gpt-6-luna","moderation":null,"output":[],"parallel_tool_calls":true,"presence_penalty":0.0,"previous_response_id":null,"prompt_cache_key":null,"prompt_cache_retention":"24h","reasoning":{"context":"all_turns","effort":"none","mode":"standard","summary":null},"safety_identifier":null,"service_tier":"auto","store":true,"temperature":1.0,"text":{"format":{"type":"text"},"verbosity":"medium"},"tool_choice":"required","tool_usage":{"image_gen":{"input_tokens":0,"input_tokens_details":{"image_tokens":0,"text_tokens":0},"output_tokens":0,"output_tokens_details":{"image_tokens":0,"text_tokens":0},"total_tokens":0},"web_search":{"num_requests":0}},"tools":[{"type":"function","description":"Create a calendar event.","name":"create_event","output_schema":null,"parameters":{"type":"object","properties":{"title":{"type":"string"},"date":{"type":"string","description":"YYYY-MM-DD"},"city":{"type":"string"},"attendees":{"type":"array","items":{"type":"string"}}},"required":["title","date","city","attendees"],"additionalProperties":false},"strict":true}],"top_logprobs":0,"top_p":0.98,"truncation":"disabled","usage":null,"user":null,"metadata":{}},"sequence_number":0}


event: response.in_progress
data: {"type":"response.in_progress","response":{"id":"resp_0f94ad531e05a9b5006acbfc0552a887d1bc1a7a17e28a6ef8","object":"response","created_at":1791753221,"status":"in_progress","access_programs":null,"background":false,"completed_at":null,"error":null,"frequency_penalty":0.0,"incomplete_details":null,"instructions":null,"max_output_tokens":20,"max_tool_calls":null,"model":"gpt-6-luna","moderation":null,"output":[],"parallel_tool_calls":true,"presence_penalty":0.0,"previous_response_id":null,"prompt_cache_key":null,"prompt_cache_retention":"24h","reasoning":{"context":"all_turns","effort":"none","mode":"standard","summary":null},"safety_identifier":null,"service_tier":"auto","store":true,"temperature":1.0,"text":{"format":{"type":"text"},"verbosity":"medium"},"tool_choice":"required","tool_usage":{"image_gen":{"input_tokens":0,"input_tokens_details":{"image_tokens":0,"text_tokens":0},"output_tokens":0,"output_tokens_details":{"image_tokens":0,"text_tokens":0},"total_tokens":0},"web_search":{"num_requests":0}},"tools":[{"type":"function","description":"Create a calendar event.","name":"create_event","output_schema":null,"parameters":{"type":"object","properties":{"title":{"type":"string"},"date":{"type":"string","description":"YYYY-MM-DD"},"city":{"type":"string"},"attendees":{"type":"array","items":{"type":"string"}}},"required":["title","date","city","attendees"],"additionalProperties":false},"strict":true}],"top_logprobs":0,"top_p":0.98,"truncation":"disabled","usage":null,"user":null,"metadata":{}},"sequence_number":1}


event: response.output_item.added
data: {"type":"response.output_item.added","item":{"id":"fc_0f94ad531e05a9b5006acbfc05e44487d18438296bb239e452","type":"function_call","status":"in_progress","arguments":"","call_id":"call_t7e3IgxCdjXlMbNHlOwncu0f","name":"create_event"},"output_index":0,"sequence_number":2}


event: response.function_call_arguments.delta
data: {"type":"response.function_call_arguments.delta","delta":"{\"","item_id":"fc_0f94ad531e05a9b5006acbfc05e44487d18438296bb239e452","obfuscation":"mF7zLxjMgZ2UrJ","output_index":0,"sequence_number":3}


event: response.function_call_arguments.delta
data: {"type":"response.function_call_arguments.delta","delta":"title","item_id":"fc_0f94ad531e05a9b5006acbfc05e44487d18438296bb239e452","obfuscation":"nhATtcGaku5","output_index":0,"sequence_number":4}


event: response.function_call_arguments.delta
data: {"type":"response.function_call_arguments.delta","delta":"\":\"","item_id":"fc_0f94ad531e05a9b5006acbfc05e44487d18438296bb239e452","obfuscation":"3RsJm5VvtGrcT","output_index":0,"sequence_number":5}


event: response.function_call_arguments.delta
data: {"type":"response.function_call_arguments.delta","delta":"Weekend","item_id":"fc_0f94ad531e05a9b5006acbfc05e44487d18438296bb239e452","obfuscation":"HfQBM2nb7","output_index":0,"sequence_number":6}


event: response.function_call_arguments.delta
data: {"type":"response.function_call_arguments.delta","delta":" Pot","item_id":"fc_0f94ad531e05a9b5006acbfc05e44487d18438296bb239e452","obfuscation":"vQWyaXuAbQrt","output_index":0,"sequence_number":7}


event: response.function_call_arguments.delta
data: {"type":"response.function_call_arguments.delta","delta":"tery","item_id":"fc_0f94ad531e05a9b5006acbfc05e44487d18438296bb239e452","obfuscation":"DBsq51gd6TkJ","output_index":0,"sequence_number":8}


event: response.function_call_arguments.delta
data: {"type":"response.function_call_arguments.delta","delta":" Workshop","item_id":"fc_0f94ad531e05a9b5006acbfc05e44487d18438296bb239e452","obfuscation":"V07Ih0q","output_index":0,"sequence_number":9}


event: response.function_call_arguments.delta
data: {"type":"response.function_call_arguments.delta","delta":"\",\"","item_id":"fc_0f94ad531e05a9b5006acbfc05e44487d18438296bb239e452","obfuscation":"9GeuTYnt4PSbC","output_index":0,"sequence_number":10}


event: response.function_call_arguments.done
data: {"type":"response.function_call_arguments.done","arguments":"{\"title\":\"Weekend Pottery Workshop\",\"","item_id":"fc_0f94ad531e05a9b5006acbfc05e44487d18438296bb239e452","output_index":0,"sequence_number":11}


event: response.output_item.done
data: {"type":"response.output_item.done","item":{"id":"fc_0f94ad531e05a9b5006acbfc05e44487d18438296bb239e452","type":"function_call","status":"incomplete","arguments":"{\"title\":\"Weekend Pottery Workshop\",\"","call_id":"call_t7e3IgxCdjXlMbNHlOwncu0f","name":"create_event"},"output_index":0,"sequence_number":12}


event: response.incomplete
data: {"type":"response.incomplete","response":{"id":"resp_0f94ad531e05a9b5006acbfc0552a887d1bc1a7a17e28a6ef8","object":"response","created_at":1791753221,"status":"incomplete","access_programs":null,"background":false,"completed_at":null,"error":null,"frequency_penalty":0.0,"incomplete_details":{"reason":"max_output_tokens"},"instructions":null,"max_output_tokens":20,"max_tool_calls":null,"model":"gpt-6-luna","moderation":null,"output":[{"id":"fc_0f94ad531e05a9b5006acbfc05e44487d18438296bb239e452","type":"function_call","status":"incomplete","arguments":"{\"title\":\"Weekend Pottery Workshop\",\"","call_id":"call_t7e3IgxCdjXlMbNHlOwncu0f","name":"create_event"}],"parallel_tool_calls":true,"presence_penalty":0.0,"previous_response_id":null,"prompt_cache_key":null,"prompt_cache_retention":"24h","reasoning":{"context":"all_turns","effort":"none","mode":"standard","summary":null},"safety_identifier":null,"service_tier":"default","store":true,"temperature":1.0,"text":{"format":{"type":"text"},"verbosity":"medium"},"tool_choice":"required","tool_usage":{"image_gen":{"input_tokens":0,"input_tokens_details":{"image_tokens":0,"text_tokens":0},"output_tokens":0,"output_tokens_details":{"image_tokens":0,"text_tokens":0},"total_tokens":0},"web_search":{"num_requests":0}},"tools":[{"type":"function","description":"Create a calendar event.","name":"create_event","output_schema":null,"parameters":{"type":"object","properties":{"title":{"type":"string"},"date":{"type":"string","description":"YYYY-MM-DD"},"city":{"type":"string"},"attendees":{"type":"array","items":{"type":"string"}}},"required":["title","date","city","attendees"],"additionalProperties":false},"strict":true}],"top_logprobs":0,"top_p":0.98,"truncation":"disabled","usage":{"input_tokens":100,"input_tokens_details":{"cache_write_tokens":0,"cached_tokens":0},"output_tokens":20,"output_tokens_details":{"reasoning_tokens":0},"total_tokens":120},"user":null,"metadata":{}},"sequence_number":13}

What the library reported

Outcome

raised

Finish

{
  "raw": "max_output_tokens",
  "source": "ModelResponse.finish_reason",
  "surface": "raw",
  "value": "length"
}

Text

Value: null
Surface: absent

Tool calls

[
  {
    "arguments": {
      "INVALID_JSON": "{\"title\":\"Weekend Pottery Workshop\",\""
    },
    "arguments_parsed_ok": true,
    "arguments_raw": "{\"INVALID_JSON\":\"{\\\"title\\\":\\\"Weekend Pottery Workshop\\\",\\\"\"}",
    "id": "call_t7e3IgxCdjXlMbNHlOwncu0f",
    "name": "create_event"
  }
]

Usage

{
  "cached_input": 0,
  "input": 100,
  "output": 20,
  "reasoning": 0,
  "surface": {
    "cached_input": "raw",
    "input": "raw",
    "output": "raw",
    "reasoning": "raw",
    "total": "raw"
  },
  "total": 120
}

Stream

{
  "chunks_seen": 12,
  "completed": false,
  "used": true
}

Error

Type: pydantic_ai.exceptions.UnexpectedModelBehavior
Message: Tool 'create_event' exceeded max retries count of 0. Consider raising the retry limit, or see the docs on tool retries: https://pydantic.dev/docs/ai/tools-toolsets/tools-advanced/#tool-retries
Category: validation
Retry after: null
Stack top: pydantic_ai/tool_manager.py:523

Unsupported reason

null

Full observation JSON

{
  "elapsed_ms": 409.5917036756873,
  "error": {
    "category": "validation",
    "message": "Tool 'create_event' exceeded max retries count of 0. Consider raising the retry limit, or see the docs on tool retries: https://pydantic.dev/docs/ai/tools-toolsets/tools-advanced/#tool-retries",
    "retry_after": null,
    "stack_top": "pydantic_ai/tool_manager.py:523",
    "type": "pydantic_ai.exceptions.UnexpectedModelBehavior"
  },
  "finish": {
    "raw": "max_output_tokens",
    "source": "ModelResponse.finish_reason",
    "surface": "raw",
    "value": "length"
  },
  "format": "wiretruth.observation/v1",
  "library": {
    "api": "Agent.run_stream_events",
    "language": "python",
    "name": "pydantic-ai",
    "version": "2.61.0"
  },
  "notes": [],
  "outcome": "raised",
  "stream": {
    "chunks_seen": 12,
    "completed": false,
    "used": true
  },
  "structured": {
    "attempted": false,
    "returned_as_success": false,
    "value": null
  },
  "text": {
    "surface": "absent",
    "value": null
  },
  "tool_calls": [
    {
      "arguments": {
        "INVALID_JSON": "{\"title\":\"Weekend Pottery Workshop\",\""
      },
      "arguments_parsed_ok": true,
      "arguments_raw": "{\"INVALID_JSON\":\"{\\\"title\\\":\\\"Weekend Pottery Workshop\\\",\\\"\"}",
      "id": "call_t7e3IgxCdjXlMbNHlOwncu0f",
      "name": "create_event"
    }
  ],
  "unsupported_reason": null,
  "usage": {
    "cached_input": 0,
    "input": 100,
    "output": 20,
    "reasoning": 0,
    "surface": {
      "cached_input": "raw",
      "input": "raw",
      "output": "raw",
      "reasoning": "raw",
      "total": "raw"
    },
    "total": 120
  }
}

Fixture

recorded openai-responses/truncation.tool-call-args-stream

Provenance	Value
Recorded at	2026-10-11T21:13:41Z
Requested model	gpt-6-luna
Returned model	gpt-6-luna
CI run	https://github.com/kartsan03/wiretruth/actions/runs/38175457862

Reproduce

wiretruth serve openai-responses/truncation.tool-call-args-stream

Plain-library snippet from the shim manifest.

OpenAIResponsesModel(model, provider=OpenAIProvider(base_url=WIRETRUTH_BASE_URL_OPENAI_RESPONSES, api_key=WIRETRUTH_API_KEY))

Upstream

reported Issue

Fixed in: not specified

Reported in a comment on the token-limit issue: https://github.com/pydantic/pydantic-ai/issues/12399#issuecomment-6780480981. Tool-call arguments cut off at the limit fail validation and end in the per-tool retry limit (UnexpectedModelBehavior: Tool 'create_event' exceeded max retries count of 0), not in IncompleteToolCall; reproduced on 2.61.0 and 2.66.0 with an ExternalToolset.

History

Version	Grade
2.61.0	~ LOSSY
2.56.0	~ LOSSY