Document 250 KB per-span field size limit for LLM-as-a-judge evaluations (#35773)

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>
Co-authored-by: Esther Kim <esther.kim@datadoghq.com>

Author: 3 people

content/en/llm_observability/evaluations/custom_llm_as_a_judge_evaluations/_index.md

@@ -277,6 +277,8 @@ Assessment Criteria is not currently available for JSON evaluations.
 
 ### Define the evaluation scope: Filtering and sampling
 
+<div class="alert alert-info">Span fields used in evaluations are limited to 250 KB each. Fields exceeding this size are truncated before being sent to the LLM judge.</div>
+
 Under **Evaluation Scope**, define where and how your evaluation runs. This helps control coverage (which spans are included) and cost (how many spans are sampled).
    - **Application**: Select the application you want to evaluate.
    - **Evaluate On**: Choose one of the following: