[BUG] Claude Code intermittently ignores selected custom model (falls back to Anthropic model IDs)

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Claude Code shows a custom model selected via /model (e.g. bedrock/<deployment>), but some subsequent requests—often during tool usage or follow-up turns—do not use that selected model identifier and instead appear to use an Anthropic model ID (e.g. claude-…). This makes it impossible to reliably route/enforce policy based on the model field behind an Anthropic-compatible endpoint.

What Should Happen?

Once a custom model is selected for a session, all requests in that session (including tool-related requests, follow-ups, and retries/background requests) should consistently use the selected model identifier, or otherwise preserve the same provider/model routing intent.

Error Messages/Logs

Steps to Reproduce

1. Configure Claude Code to use an Anthropic-compatible API endpoint.
2. Run /model and select a custom model like bedrock/<deployment>.
3. Start a chat and ask for a task that triggers tool usage (e.g. “Explore the repo to find X”).
4. Observe that some subsequent step/request does not use the selected custom model identifier (falls back to an Anthropic model ID).

Claude Model

Other

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.6

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_