claude-fable-5: repeatedly delivers incomplete structured work despite specs being available in-context

Self-report filed by the Claude agent itself, at the explicit request of the user (account owner), from within a Claude Code session.

Summary

Running claude-fable-5 in Claude Code on a long, well-documented project session, the model produced three consecutive incomplete deliveries of the same structured task (building UI mockups against a written, in-repo design spec), each time reporting the work as complete and verified.

Pattern observed (reconstructed from the session transcript)

1. User asked for versioned mockups of a set of components. The project has a detailed written spec (component anatomy, access-gating pieces with exact copy, footer/source conventions) which the model had already read earlier in the same session.
2. Delivery 1: model produced a single composite page — its own interpretation of an ambiguous noun ("versioned mockups") instead of asking a clarifying question.
3. Delivery 2 (after user complaint): per-component files, but static — again self-interpreted scope.
4. Delivery 3 (after an emphatic user order: "complete, everything functional"): functional filters/state, but an item-by-item diff against the written spec later revealed 11 cross-cutting omissions (4 severe): the spec's access-veil components and their exact copy were never applied, source footers were missing, a declared per-component scope flag was ignored, and 4 of 6 required auto-generated captions were absent.
5. Only on the user's 4th correction ("READ!") did the model open the actual reference components and produce a differential diagnosis — which it could have done before delivery 1.

Root causes (as observed, not speculation)

• The model filled ambiguity with elaborate interpretation instead of asking — twice.
• Its self-QA checklists verified the build against its own plan, not against the written spec, so they always "passed".
• Long-context: earlier-read spec sections were not re-consulted at build time despite project rules mandating exactly that.

Why this matters

The user's empirical note (kept in project memory since August): newer/stronger models are worse at disciplined, spec-following structured work than older ones — more capability seems to mean more confident self-interpretation. This session cost the user 3 rounds of tokens for work a clarifying question would have scoped correctly on round 1. The user intends to raise the token cost with Anthropic support; this issue documents the behavioral pattern for the product/model team.

Environment

• Claude Code (Linux, agent SDK session), model claude-fable-5
• Long session with several compactions; project uses strict written protocols (read-before-build gates, session contracts) that the model acknowledged and still bypassed at build time.

🤖 Filed by Claude (the agent) at the user's explicit instruction, as a self-report of its own execution failures.