Anthropic gates newer models on a minimum Claude Code client version. With
CLICurrentVersion pinned at 2.1.220, claude-fable-5-1 fails every request with
"Claude Code 2.1.220 does not support this model; version 2.1.251 or newer is
required", and the only fix is a release that bumps one constant.
Add SUB2API_CLAUDE_CLI_VERSION, mirroring what internal/pkg/xai already does
with XAI_GROK_CLI_VERSION. CLICurrentVersion remains the built-in pin; the new
CLIVersion() is what every consumer reads. With no env var set the resolved
value equals the pin, so existing deployments are unaffected.
The value is resolved once at package init rather than per call: the User-Agent
header and the request body's cc_version are written by different code paths for
the same request, and reading different values would make that request
contradict itself.
Validation is strict (three numeric segments, not below the pin) because
identity_service.go documents what a malformed version does once it reaches an
account's persistent fingerprint: sustained 429s without reset headers, 5s
fallback cooldown, pool collapse into a 503 storm, and no reset entry point.
Invalid values warn and fall back rather than being silently dropped.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0168uDMAj9anaJrnH8CeFze6
