Zero-model mid-session backend switching with shell commands

[oloflun]

What

Switch between DeepSeek and Anthropic backends mid-session without model involvement. Type !ds or !ant directly in Claude Code -- the shell executes the switch before any model call. No /command delay, no skill/agent loading, works even when the current backend is completely unreachable.

How it works

A lightweight 3-server routing proxy (routing-proxy.mjs) sits between Claude Code and the API backends. It reads a mode file on every request and routes to the appropriate backend:

Claude Code -> Router (:3199) -> reads mode file -> DeepSeek (:3200) or Anthropic (:3201)

• !ds / !ant / !backend are Bash scripts that write to the session mode file. Claude Code's ! prefix runs them at the CLI layer before any API request.
• Each session gets its own proxy on unique ports with a per-session mode file, so switching one session doesn't affect others.
• Auto-fallback: if Anthropic returns 401/402/403 (no credits), the router silently retries via DeepSeek and switches the mode.
• Backward compatible: CLI args for mode file path and router port are optional -- falls back to global defaults.

PowerShell session management (master commands)

From any PowerShell window:

sessions          # list all running sessions with ports and modes
ds                # switch current session to DeepSeek
ant               # switch current session to Anthropic
backend           # show current session backend
ds -All           # master switch: ALL sessions to DeepSeek
ant -All          # master switch: ALL sessions to Anthropic
ds -Session 3202  # target a specific session by port

Functions auto-detect the current session via ANTHROPIC_BASE_URL env var. Auto-refresh from disk -- no manual profile reload needed.

Changes

• New file: proxy/routing-proxy.mjs -- the routing proxy. Accepts optional 4th arg (mode file path) and 5th arg (router port). Backend ports derived as routerPort+1 / routerPort+2. Status endpoint at /_router/status.

Companion setup (one-time, on user machine)

Three Bash scripts in ~/.local/bin/ and PowerShell profile functions provide the in-session commands and session management. See the companion Gist linked below for full setup.

🤖 Generated with Claude Code