Claude Code + GitHub Copilot

Use Claude Code's editor and CLI workflow while routing Layer 3 through your existing GitHub Copilot subscription via Isartor. Repeated prompts are still deflected by Isartor's L1a/L1b cache first, ad L2 SLM (if turned on) so cache hits consume zero Copilot quota.

Current status: experimental. The connector and Copilot-backed L3 routing are implemented, but Isartor's Anthropic compatibility surface is still text-oriented today. That means plain Claude Code prompting works best right now; more advanced Anthropic tool-use blocks may still require follow-up work.

Prerequisites

1. Active GitHub Copilot subscription
2. Isartor installed
3. Claude Code installed

# Install Isartor
curl -fsSL https://raw.githubusercontent.com/isartor-ai/Isartor/main/install.sh | sh

# Install Claude Code
npm install -g @anthropic-ai/claude-code

Setup

Path A — Interactive authentication (recommended)

isartor connect claude-copilot

This starts GitHub device-flow authentication, stores the OAuth token locally, updates ./isartor.toml, and writes Claude Code settings into ~/.claude/settings.json.

When no --github-token is provided, Isartor now prefers browser/device-flow OAuth first. It will reuse a previously saved OAuth credential, but it will not silently reuse legacy saved PATs.

Path B — Use an existing GitHub token

isartor connect claude-copilot --github-token ghp_YOUR_TOKEN

Use --github-token only when you intentionally want to override the default browser login flow with a PAT.

Path C — Choose custom Copilot models

isartor connect claude-copilot \
  --github-token ghp_YOUR_TOKEN \
  --model gpt-4.1 \
  --fast-model gpt-4o-mini

After the command finishes, restart Isartor so the new Layer 3 config is loaded:

isartor stop
isartor up --detach
claude

One-click smoke test

./scripts/claude-copilot-smoke-test.sh
# or
make smoke-claude-copilot

The script automatically:

• reads the saved Copilot credential from ~/.isartor/providers/copilot.json
• picks a supported Copilot-backed model
• starts a temporary Isartor instance
• runs a Claude Code smoke prompt
• prints an ROI demo showing L3, L1a exact-hit, and L1b semantic-hit behavior

What the command changes

~/.claude/settings.json

The command writes these Claude Code environment overrides:

./isartor.toml

The command also sets Isartor Layer 3 to use the Copilot provider:

llm_provider = "copilot"
external_llm_model = "claude-sonnet-4.5"
external_llm_api_key = "ghp_..."
external_llm_url = "https://api.githubcopilot.com/chat/completions"

Available Copilot-backed models

What Isartor saves

Without Isartor:

Every Claude Code prompt -> GitHub Copilot API -> quota consumed

With Isartor:

Repeated prompt (L1a hit) -> served locally -> 0 Copilot quota
Similar prompt (L1b hit)  -> served locally -> 0 Copilot quota
Novel prompt (cache miss) -> forwarded to Copilot -> quota consumed

Example session:

100 Claude Code prompts
  40 exact repeats      -> L1a -> 0 quota
  25 semantic variants  -> L1b -> 0 quota
  35 novel prompts      -> L3  -> 35 Copilot-backed requests

Result: 35 routed requests instead of 100

Limitations

• GitHub Copilot output is capped; Isartor writes CLAUDE_CODE_MAX_OUTPUT_TOKENS=16000
• The current /v1/messages compatibility path is still text-oriented, so some advanced Anthropic tool-use flows may not yet behave exactly like direct Anthropic routing
• Extended-thinking / provider-specific Anthropic features are not preserved
• If the chosen Copilot model is unavailable to your account, requests fail instead of silently falling back to Anthropic

Disconnect

isartor connect claude-copilot --disconnect

This restores the backed-up ~/.claude/settings.json and ./isartor.toml.

Troubleshooting