[DOCS] Auto mode classifier Fable 5 fallback added in v2.1.176 is not described in `auto-mode-config.md`

1. TITLE

Auto mode classifier Fable 5 fallback added in v2.1.176 is not described in auto-mode-config.md

2. WHAT KIND OF DOCUMENTATION ISSUE IS THIS?

• [x] Missing documentation (feature not documented)
• [ ] Unclear/confusing documentation
• [ ] Incorrect/outdated documentation
• [ ] Typo or formatting issue
• [ ] Missing code examples
• [ ] Broken links
• [ ] Other

3. WHERE DID YOU ENCOUNTER THIS ISSUE?

https://code.claude.com/docs/en/auto-mode-config

4. WHICH SPECIFIC SECTION OR TOPIC NEEDS IMPROVEMENT?

The "Configure auto mode" page has no mention of Fable 5 or how the classifier behaves when Fable 5 is selected in organizations without Opus 4.8 enabled.

5. CURRENT DOCUMENTATION

auto-mode-config.md describes autoMode.environment, hard_deny, soft_deny, and allow configuration, plus the claude auto-mode CLI subcommands. It does not mention Fable 5, the classifier's model fallback, or any interaction between the selected model and the classifier.

model-config.md describes a separate automatic fallback for Fable 5 in third-party providers:

The fallback target must resolve to an Opus model: the value of ANTHROPIC_DEFAULT_OPUS_MODEL if set, otherwise an Opus 4.8 entry in the provider's model list.

But this is documented as a model-picker fallback, not an auto mode classifier fallback.

6. WHAT'S WRONG OR MISSING?

v2.1.176 added a classifier-side fallback for Fable 5:

Fixed auto mode failing on Fable 5 for organizations without Opus 4.8 enabled — the classifier now falls back to the best available Opus model

Users running auto mode with Fable 5 in an organization where Opus 4.8 is not yet enabled have no documentation explaining this fallback. Without it, an admin reading the auto mode page has no way to know:

• That Fable 5 + auto mode is supported
• What happens when Opus 4.8 is unavailable in their org
• That the classifier selects "the best available Opus model" automatically

7. SUGGESTED IMPROVEMENT

Add a short note to auto-mode-config.md, near the existing "Requirements" or "How the classifier works" content, such as:

Fable 5 model fallback: When auto mode is running under Fable 5 and the classifier routes a request that Fable 5 cannot handle (typically a flagged safety classifier result in cybersecurity or biology domains), the classifier falls back to the best available Opus model. In organizations without Opus 4.8 enabled, the classifier uses the next-highest Opus version. To pin the fallback target, set ANTHROPIC_DEFAULT_OPUS_MODEL in your environment or managed settings.

8. IMPACT

• [ ] High - Prevents users from using a feature
• [x] Medium - Makes feature difficult to understand
• [ ] Low - Minor confusion or inconvenience

9. ADDITIONAL CONTEXT

Affected Pages:

| Page | Context |
|------|---------|
| https://code.claude.com/docs/en/auto-mode-config | Primary location; should describe Fable 5 fallback |
| https://code.claude.com/docs/en/model-config | Already documents the model-picker fallback for Fable 5; could cross-reference the auto mode fallback |

Source: Changelog v2.1.176