GitHub Copilot's /chat/completions and /responses endpoints never surface
prompt-cache token counts (cached_tokens) for Claude models, and round-tripping
Claude tool_use/tool_result/thinking content blocks through the OpenAI shape
is lossy. Copilot also exposes an Anthropic-native /v1/messages shim that
reports cached_tokens correctly and accepts native content blocks as-is.
Tag each github registry claude-* model with targetFormat: "claude" so
chatCore.ts translates the request to Anthropic-native shape before the
executor ever sees it (the same mechanism opencode/zen's Qwen entries and
opencode/go already use), and teach the github executor's buildUrl() /
buildHeaders() to dispatch those models at the new messagesUrl
(api.githubcopilot.com/v1/messages) with the required anthropic-version
header. transformRequest() now skips its /chat/completions-only quirks
(content-part flattening, trailing-assistant-prefill drop, the
response_format-as-system-prompt workaround) for the native path — the first
would destroy native tool_use/tool_result blocks, the prefill drop is
unnecessary because the real Anthropic API supports assistant prefill, and
the response_format workaround is superseded by the generic openai-to-claude
translator's own JSON-mode handling.
Co-authored-by: luoyide <ydhome.code@gmail.com>
Inspired-by: https://github.com/decolua/9router/pull/2608
b2b0fafb71