Anthropic /v1/messages rejects cache_control.scope that Anthropic direct accepts

[camwest]

What Happened?

Portkey's Anthropic-compatible /v1/messages endpoint rejects a request body that Anthropic direct accepts.

The incompatibility appears to be cache_control.scope = "global" on a system content block when using Claude Code / Claude Agent SDK prompt caching scope betas.

Observed behavior:

• Direct Anthropic: 200 OK
• Portkey /v1/messages: 400 invalid_request_error
• Error: anthropic error: system.1.cache_control.ephemeral.scope: Extra inputs are not permitted

This is breaking Claude Code / Claude Agent SDK traffic routed through Portkey for us.

What Should Have Happened?

Portkey should accept and forward the same Anthropic-compatible request body that Anthropic direct accepts, including cache_control.scope = "global" when the request uses Anthropic's prompt-caching-scope beta.

Relevant Code Snippet

Minimal raw repro:

const body = {
  model: 'claude-opus-4-6',
  max_tokens: 32,
  system: [
    {
      type: 'text',
      text: "You are Claude Code, Anthropic's official CLI for Claude, running within the Claude Agent SDK.",
    },
    {
      type: 'text',
      text: 'Session-specific guidance. Reply with ok.',
      cache_control: { type: 'ephemeral', scope: 'global' },
    },
  ],
  messages: [
    { role: 'user', content: [{ type: 'text', text: 'Reply with ok.' }] },
  ],
  stream: false,
};

const anthropicBeta =
  'claude-code-20250219,interleaved-thinking-2025-05-14,context-management-2025-06-27,prompt-caching-scope-2026-01-05,effort-2025-11-24';

Direct Anthropic request:

curl https://api.anthropic.com/v1/messages \
  -H 'content-type: application/json' \
  -H 'anthropic-version: 2023-06-01' \
  -H "anthropic-beta: $ANTHROPIC_BETA" \
  -H "x-api-key: $ANTHROPIC_API_KEY" \
  -d "$BODY"

Result:

{
  "status": 200,
  "content": [{ "type": "text", "text": "ok" }]
}

Portkey request with a single Anthropic target:

curl https://api.portkey.ai/v1/messages \
  -H 'content-type: application/json' \
  -H 'authorization: Bearer dummy' \
  -H 'anthropic-version: 2023-06-01' \
  -H "anthropic-beta: $ANTHROPIC_BETA" \
  -H "x-portkey-api-key: $PORTKEY_API_KEY" \
  -H 'x-portkey-config: {"strategy":{"mode":"fallback","on_status_codes":[429,500,502,503,529]},"targets":[{"virtual_key":"anthropic-default-prod","override_params":{"model":"claude-opus-4-6"}}]}' \
  -d "$BODY"

Result:

{
  "error": {
    "message": "anthropic error: system.1.cache_control.ephemeral.scope: Extra inputs are not permitted",
    "type": "invalid_request_error"
  },
  "provider": "anthropic"
}

Additional context:

• @anthropic-ai/claude-agent-sdk@0.2.89
• claude-cli/2.1.89
• This field is emitted by Claude Code / Agent SDK request construction, not by our application prompt builder.
• Portkey docs appear to document cache_control.type and ttl, but I could not find mention of cache_control.scope.

If helpful, I can provide a fully self-contained Node repro as well.