[DOCS] Gateway background session naming docs omit main-model fallback when no Haiku model is configured

Documentation Type

Missing documentation (feature not documented)

Documentation Location

https://code.claude.com/docs/en/model-config

Section/Topic

Environment variables and Pin models for third-party deployments

Current Documentation

The docs currently say:

| ANTHROPIC_DEFAULT_HAIKU_MODEL | The model to use for haiku, or background functionality |

Set all three model environment variables to specific version IDs as part of your initial setup. Pinning lets you control when your users move to a new model.

Related background-session docs say:

Type a prompt in the input at the bottom of agent view and press Enter to start a new background session. The session is named automatically from the prompt; rename it later with Ctrl+R.

And the gateway docs say:

By default, Claude Code uses standard model names for the selected API format.

If your gateway uses model names that do not match the discovery filter, use the environment variables documented in Model configuration to add them manually.

What's Wrong or Missing?

The docs do not explain how background session auto-naming behaves on custom ANTHROPIC_BASE_URL gateways.

Specifically, they do not say whether auto-naming requires ANTHROPIC_DEFAULT_HAIKU_MODEL to be configured on the gateway, or whether Claude Code falls back to the session's main model when no Haiku model is configured.

That leaves gateway operators with an important gap: the docs promise that background sessions are auto-named and separately say that ANTHROPIC_DEFAULT_HAIKU_MODEL powers background functionality, but they never connect those statements for gateway deployments.

Suggested Improvement

Add a short note in the model-configuration docs, with a cross-reference from the gateway page, clarifying which model powers background session auto-naming on custom gateways.

For example, document that for custom ANTHROPIC_BASE_URL gateways Claude Code uses ANTHROPIC_DEFAULT_HAIKU_MODEL for this background functionality when it is configured, and as of v2.1.141 falls back to the session's main model when no Haiku model is configured.

Also add one concrete gateway example showing the difference between:

• a deployment that explicitly pins ANTHROPIC_DEFAULT_HAIKU_MODEL, and
• a deployment that only configures the main model and relies on the fallback behavior.

Impact

Medium - Makes feature difficult to understand

Additional Context

Affected Pages:

| Page | Context |
|------|---------|
| https://code.claude.com/docs/en/model-config | Documents ANTHROPIC_DEFAULT_HAIKU_MODEL as the model for background functionality but not the gateway fallback behavior |
| https://code.claude.com/docs/en/llm-gateway | Explains custom ANTHROPIC_BASE_URL gateway model selection but not how background auto-naming is routed |
| https://code.claude.com/docs/en/agent-view | Promises that background sessions are named automatically from the prompt |

Total scope: 3 pages affected

Version context: v2.1.141 changelog entry indicates background jobs on custom ANTHROPIC_BASE_URL gateways now get auto-named by using the main model when no Haiku model is configured.