[DOCS] Environment variables page missing ANTHROPIC_BETAS env var

Documentation Type

Missing documentation (feature not documented)

Documentation Location

https://code.claude.com/docs/en/env-vars

Section/Topic

Environment variables reference table

Current Documentation

No documentation currently exists for ANTHROPIC_BETAS. The env-vars page lists a comprehensive table of environment variables but does not include ANTHROPIC_BETAS. The related but distinct CLAUDE_CODE_DISABLE_EXPERIMENTAL_BETAS variable is documented on the LLM gateway page, but it serves the opposite purpose (disabling betas rather than enabling them).

What's Wrong or Missing?

Changelog v2.1.78 fixed ANTHROPIC_BETAS being silently ignored when using Haiku models. The fix confirms this is a supported environment variable, but users cannot discover it from the documentation.

Users who want to enable specific Anthropic API beta features when using Claude Code have no documented mechanism to do so. The ANTHROPIC_BETAS variable presumably accepts beta feature header values (comma-separated), but without documentation users cannot know the correct format or available values.

Suggested Improvement

Add an entry to the env-vars table:

| Variable | Description |
|----------|-------------|
| ANTHROPIC_BETAS | Comma-separated list of Anthropic API beta feature headers to enable (e.g., beta-feature-1,beta-feature-2). Applied to all API requests. |

Add a note clarifying the relationship with CLAUDE_CODE_DISABLE_EXPERIMENTAL_BETAS (which disables Claude Code's own experimental betas, separate from API beta headers).

Impact

Medium - Makes feature difficult to understand

Additional Context

Affected Pages:

| Page | Context |
|------|---------|
| https://code.claude.com/docs/en/env-vars | Environment variables reference table |
| https://code.claude.com/docs/en/llm-gateway | Documents CLAUDE_CODE_DISABLE_EXPERIMENTAL_BETAS (related but distinct) |

Total scope: 2 pages affected

Source: Changelog v2.1.78

Fixed ANTHROPIC_BETAS environment variable being silently ignored when using Haiku models