🐛 Bug Report: Anthropic event emitter leaks `NOT_GIVEN` sentinel into log Body, breaking OTLP log export

[marians]

Which component is this bug for?

Anthropic Instrumentation

📜 Description

When the Anthropic instrumentation is run in event-logging mode (use_legacy_attributes=False, with an event_logger_provider configured), a messages.create() call that omits tools causes the emitted GenAI input event to contain the Anthropic SDK sentinel anthropic.NOT_GIVEN in its log record Body. The OTLP log exporter cannot serialize anthropic.NotGiven, so the entire log batch fails to export with:

opentelemetry.sdk._shared_internal - ERROR - Exception while exporting Log.
...
Exception: Invalid type <class 'anthropic.NotGiven'> of value NOT_GIVEN

Root cause

In opentelemetry/instrumentation/anthropic/event_emitter.py, emit_input_events():

    if kwargs.get("system"):                       # truthiness — NOT_GIVEN is falsy, correctly skipped
        emit_event(MessageEvent(content=kwargs.get("system"), role="system"), event_logger)
    for message in kwargs.get("messages"):
        emit_event(MessageEvent(content=message.get("content"), role=message.get("role")), event_logger)
    if kwargs.get("tools") is not None:            # BUG: `is not None` lets NOT_GIVEN through
        emit_event(
            MessageEvent(content={"tools": kwargs.get("tools")}, role="user"),   # NOT_GIVEN placed in Body
            event_logger,
        )

When a caller omits tools, the Anthropic SDK passes tools=anthropic.NOT_GIVEN. NOT_GIVEN is not None evaluates to True, so the guard passes and the sentinel object is put verbatim into the MessageEvent body
({"tools": NOT_GIVEN}). It then flows into the OTel LogRecord body, and the OTLP protobuf encoder
(opentelemetry/exporter/otlp/proto/common/_internal/_log_encoder) raises on the unsupported type.

Note the inconsistency: the system branch immediately above uses a truthiness check (if kwargs.get("system"):), which correctly drops NOT_GIVEN (bool(NOT_GIVEN) is False). Only the tools branch uses is not None, so
only tools leaks the sentinel.

👟 Reproduction steps

1. Instrument Anthropic in event mode with an OTLP log exporter:

   from opentelemetry.instrumentation.anthropic import AnthropicInstrumentor
   from opentelemetry.sdk._events import EventLoggerProvider
   from opentelemetry.sdk._logs import LoggerProvider
   from opentelemetry.sdk._logs.export import BatchLogRecordProcessor
   from opentelemetry.exporter.otlp.proto.grpc._log_exporter import OTLPLogExporter
   
   logger_provider = LoggerProvider()
   logger_provider.add_log_record_processor(BatchLogRecordProcessor(OTLPLogExporter()))
   AnthropicInstrumentor().instrument(
       event_logger_provider=EventLoggerProvider(logger_provider),
   )
   # equivalent to use_legacy_attributes=False + event logging enabled

2. Make a messages.create() call without the tools argument (so the SDK defaults it to NOT_GIVEN):

   import anthropic
   client = anthropic.Anthropic()
   client.messages.create(
       model="claude-sonnet-4-...",
       max_tokens=256,
       system="You are a helpful assistant.",
       messages=[{"role": "user", "content": "Hi"}],
       # note: no `tools=` argument
   )

3. On the next log batch export, the exporter crashes with Invalid type <class 'anthropic.NotGiven'> of value NOT_GIVEN and the batch is dropped.

👍 Expected behavior

Omitted optional parameters (represented by anthropic.NOT_GIVEN) should not be emitted into event bodies. The input event should simply not include a tools entry when no tools were passed — mirroring the existing system handling.

👎 Actual Behavior with Screenshots

MessageEvent(content={"tools": NOT_GIVEN}, role="user") is emitted, placing a non-serializable anthropic.NotGiven into the OTel log Body. The OTLP log exporter then fails to encode the batch and all log records in that batch are lost. A full traceback is logged on every export interval.

🤖 Python Version

3.13

📃 Provide any additional context for the Bug.

Suggested fix

Guard tools with a truthiness check, consistent with system (handles both
NOT_GIVEN and empty lists):

    if kwargs.get("tools"):        # NOT_GIVEN and [] are both falsy → skipped
        emit_event(
            MessageEvent(content={"tools": kwargs.get("tools")}, role="user"),
            event_logger,
        )

(Alternatively, sanitize all NOT_GIVEN values out of kwargs before building events, which also future-proofs emit_response_events and any other sentinel leakage.)

Stack trace

opentelemetry.sdk._shared_internal - ERROR - Exception while exporting Log.
Traceback (most recent call last):
  File ".../opentelemetry/sdk/_shared_internal/__init__.py", line 179, in _export
    self._exporter.export(...)
  File ".../opentelemetry/exporter/otlp/proto/grpc/_log_exporter/__init__.py", line 116, in export
    return OTLPExporterMixin._export(self, batch)
  File ".../opentelemetry/exporter/otlp/proto/grpc/exporter.py", line 392, in _export
    request=self._translate_data(data),
  File ".../opentelemetry/exporter/otlp/proto/grpc/_log_exporter/__init__.py", line 110, in _translate_data
    return encode_logs(data)
  File ".../_log_encoder/__init__.py", line 58, in _encode_log
    body=_encode_value(body, allow_null=True),
  File ".../_internal/__init__.py", line 95, in _encode_value
    _encode_key_value(str(k), v, allow_null=allow_null)
  File ".../_internal/__init__.py", line 107, in _encode_key_value
    key=key, value=_encode_value(value, allow_null=allow_null)
  File ".../_internal/__init__.py", line 100, in _encode_value
    raise Exception(f"Invalid type {type(value)} of value {value}")
Exception: Invalid type <class 'anthropic.NotGiven'> of value NOT_GIVEN

Additional context

• Surfaced via kagent (v0.9.6), which enables event-mode GenAI logging and routes events to an OTLP LoggerProvider. The crash reproduces on the direct Anthropic API path.
• It reliably fires on requests with no tools — e.g. ADK's event-compaction summarizer call (which sends no tools) — while normal tool-carrying turns serialize fine.
• Functional impact is limited to telemetry: the LLM calls themselves succeed (HTTP 200); only the GenAI log export is lost, plus recurring traceback noise. Traces (separate exporter) are unaffected.

Versions

• opentelemetry-instrumentation-anthropic: 0.52.5
• anthropic: 0.104.1
• opentelemetry-exporter-otlp-proto-common: 1.38.0

👀 Have you spent some time to check if this bug has been raised before?

• I checked and didn't find similar issue

Are you willing to submit PR?

None

[nidhithippana]

Hi, I've opened a PR to fix this — changed the is not None guard on the tools branch in emit_input_events() to a truthiness check, consistent with how the system branch above it already handles NOT_GIVEN. Also added a regression test. Feel free to merge if it looks good!