API 400 error when submitting image-only message (empty text content block)

Summary

When submitting a message containing only an image (no text), Claude Code sends an API request with an empty text content block, causing the Anthropic API to reject the request with a 400 error.

Error

API Error: 400 {"type":"error","error":{"type":"invalid_request_error","message":"messages: text content blocks must be non-empty"},"request_id":"req_011Ca9cUr9rBmqKijmBWEqps"}

Retries produce the same error with different request IDs — the bad payload is sent every time.

Reproduction

1. Start a Claude Code session
2. Paste or attach an image into the prompt without typing any text
3. Submit

Expected: The image is accepted as the user turn (either alone, or with the empty text block stripped).
Actual: API Error: 400 — text content blocks must be non-empty.

Environment

• Claude Code CLI
• Model: Opus 4.7 (1M context)
• Platform: macOS (Darwin 25.4.0)

Likely Fix

Strip empty text content blocks before sending, or omit the text block entirely when the user turn only contains an image.

Screenshot

!API 400 error