[FEATURE] Add option to switch models after session starts in web interface

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

When using Claude Code through the web interface (claude.ai), there is currently no option to switch between different models (e.g., Sonnet, Opus, Haiku) after a session has started.

In the terminal CLI version, users can use the /model command to switch models mid-session. However, this functionality is not available in the web interface.

This means if I start a Claude Code session and realize I need a more capable model (like Opus for complex tasks) or a faster/cheaper model (like Haiku for simple tasks), I have to end the session and start a new one, losing the conversation context.

Proposed Solution

Add a model selector dropdown or a /model command in the web interface that allows users to switch between available models (Sonnet, Opus, Haiku) during an active Claude Code session, similar to how it works in the CLI version.

Alternative Solutions

Currently, the only workaround is to end the session and start a new one with a different model, which loses all conversation context.

Priority

Medium - Would be very helpful

Feature Category

CLI commands and flags

Use Case Example

Scenario: Working on a complex debugging task that evolves during the session

1. I start a Claude Code session in the web interface with Sonnet to explore a bug in my codebase
2. Claude helps me identify that the issue is more complex than expected - it involves intricate race conditions across multiple services
3. I want to switch to Opus for deeper analysis and more sophisticated debugging strategies
4. Currently, I have to:

• End the current session
• Start a new session with Opus
• Re-explain the entire context and what we've discovered so far
• Lose the conversation history and momentum

With this feature, I could simply switch to Opus mid-session and continue seamlessly with all the context preserved.

Another example: I start with Opus for complex architectural planning, then want to switch to Haiku for simple repetitive tasks like generating boilerplate code - saving cost while keeping the conversation context.

Additional Context

_No response_