Pydantic AI Updates: April 9, 2026

1. Pydantic AI v1.78.0 Adds OpenTelemetry Token Spans and Enhanced Tool Introspection

Pydantic AI. Pydantic AI v1.78.0 adds cached token span attributes per the OpenTelemetry spec for improved observability of token usage across agent workflows, expands the ToolDefinition class with return_schema and function_signature parameters for better tool introspection, and introduces SetToolMetadata for dynamic tool configuration at runtime. Source