Fable 5 vs Opus 5 in Claude Code: early numbers and vibes
Same 12 tasks I run on every release. Fable took 9, Opus took 2, one tie — but the interesting part isn't the score.
Claude Code2.4.18 repliesDiscussion2h ago
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Released Jul 31, 2026. Everything the community has pinned to this exact release.
Same 12 tasks I run on every release. Fable took 9, Opus took 2, one tie — but the interesting part isn't the score.
Four ways to run the same agent. Which one should someone actually start with, and why?
Codex is fast and overshoots; Claude is a pedantic reviewer. Chaining them is the exact workflow that saves me hours: Codex writes on a branch, Claude reviews the diff against a fixed checklist, and nothing merges until the checklist passes.
2.4.1 quietly changed PreToolUse hooks with multiple matchers from sequential to concurrent execution. If your second hook depends on a file the first one writes, it now races. At least 12 published recipes on this site assume sequential order.
Mine grew to 600 lines and the agent ignores most of it. Time to talk about what earns a slot in the most expensive real estate in your repo.
In a 400k-line workspace, an unscoped agent burns half its context discovering packages it will never touch — then edits one it shouldn't. Run the agent from the package directory, deny writes outside it, and hand it the workspace-level commands it still needs.
Long sessions die one of two deaths: the bill or the compaction. This is the freelancer's version of token discipline — measure per task, keep the context lean on purpose, and checkpoint state to files so a fresh session costs you minutes, not the afternoon.
Agent-authored edits keep landing with `!` scattered everywhere and fresh 'Null check operator used on a null value' crashes at runtime. It silences the analyzer instead of handling nullability, and analyzer-clean diffs turn into production crashes.
Reproduction evidence on 2.4.1
| Problem | Version | OS | Outcome | Status |
|---|---|---|---|---|
| Claude Code 2.4.1 changed hook execution order — parallel matchers now run concurrently | 2.4.1 | macOS 15.5 | Reproduced | Active Issue |
| Claude Code 2.4.1 changed hook execution order — parallel matchers now run concurrently | 2.4.1 | Fedora 42 | Reproduced | Active Issue |
| MCP server memory leak in long sessions | 2.4.1 | macOS 15.5 | Reproduced | Active Issue |
| Agent edits reintroduce null-safety errors in Flutter | 2.4.1 | macOS 15.5 |
| Not reproduced |
| Needs Verification |
| Agent edits reintroduce null-safety errors in Flutter | 2.4.1 | macOS 15.5 | Reproduced | Needs Verification |
| Claude Code ignores repository instructions after compaction | 2.4.1 | Windows 11 | Reproduced | Active Issue |
| Claude Code keeps rewriting package-lock.json | 2.4.1 | macOS 15.5 | Reproduced | Workaround Verified |
| Worktree sessions inherit .env from the main checkout | 2.4.1 | Ubuntu 24.04 | Reproduced | Active Issue |