---
title: "Claude Opus 4.8 and Sonnet 5 seem worse at tool calls than older models, likely due to post-training that assumes Claude Code-like harnesses as targets (Armin Ronacher/Armin Ronacher's Thoughts and Writings) — Stuff That Spins"
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date: "2026-07-06T08:35:01+00:00"
modified: "2026-07-06T12:01:53.869118+00:00"
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# Claude Opus 4.8 and Sonnet 5 seem worse at tool calls than older models, likely due to post-training that assumes Claude Code-like harnesses as targets (Armin Ronacher/Armin Ronacher's Thoughts and Writings)

**Source:** Unknown  
**Published:** July 6, 2026  
**Original:** https://www.techmeme.com/260706/p4#a260706p4  

## On this page

- [Overview](#overview)

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## Overview

Armin Ronacher / Armin Ronacher's Thoughts and Writings: Claude Opus 4.8 and Sonnet 5 seem worse at tool calls than older models, likely due to post-training that assumes Claude Code-like harnesses as targets &mdash; A very strange Pi issue sent me down a rabbit hole over the last two days. The short version is that newer Claude models sometimes call Pi's edit tool &hellip;

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