Pydantic AI 2.59.0 fixes web_fetch security issue and adds agent features

News AI Agent Infrastructure

  • Pydantic AI 2.59.0 fixes a high-severity issue in which converting attacker-controlled HTML with many elements through web_fetch_tool could delay unrelated work in the same process; the fix is also in v1.107.9.
  • The new DaytonaSandbox provides a workspace where Coder, Shell, FileSystem, and other harness capabilities run inside a Daytona sandbox.
  • The release adds ElevenLabsRealtimeModel for Eleven Realtime speech-to-speech models.
  • It introduces provider-neutral model error categories and lets TemporalDurability exclude selected categories from retries.
  • SummarizingCompaction now escapes the summarizer transcript so tool output cannot forge messages.

Our take

For workflows that fetch untrusted HTML with web_fetch, upgrading from v2.58.0 has a direct security rationale; teams on the v1 line also have v1.107.9 as a patched option. The release does not specify the element count that triggers the delay or provide performance measurements, so teams should test their own fetched content rather than assume a general latency improvement.

Sources

  1. pydantic-ai v2.59.0 (2026-10-20) · Pydantic AI Releases

Further reading

  1. pydantic-ai v1.107.9 (2026-10-20) · Pydantic AI Releases

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