Anthropic has reportedly enrolled Fable 5 sessions running Claude Code version 2.1.236 or later in a server-side experiment that reduces the product’s effort scale. Older Claude Code versions and Opus 5 are reportedly not affected. The change is likely an A/B test, according to the X post, so it may not appear for every user. Users for whom the “high” effort setting behaves more like the previous “low” setting may be part of the test group.