ollama - 💡(How to fix) Fix Anthropic compatibility: image content blocks are dropped when forwarded to vision-capable cloud models (v0.21.0) [2 comments, 2 participants]

Bug description

When using Ollama's Anthropic-compatible endpoint (POST /v1/messages) with a vision-capable cloud model such as kimi-k2.6:cloud, image content blocks in the request are silently dropped before being forwarded to the model. The model only receives the surrounding text, so it responds as if no image was attached.

This breaks Claude Code (and any other Anthropic-API client) when combined with tools that send screenshots — e.g. the computer-use MCP server — since the model has no idea an image was ever sent.

Environment

• Ollama: v0.21.0 (confirmed via /api/version)
• Model: kimi-k2.6:cloud — ollama show reports Capabilities: vision, thinking, completion, tools
• OS: Windows 11
• Client: curl (identical behavior seen via Claude Code CLI)

Reproduction

curl -s http://localhost:11434/v1/messages \
  -H "Content-Type: application/json" \
  -H "anthropic-version: 2023-06-01" \
  -d '{
    "model": "kimi-k2.6:cloud",
    "max_tokens": 200,
    "messages": [{
      "role": "user",
      "content": [
        {"type": "text", "text": "Describe this tiny test image in one sentence."},
        {"type": "image", "source": {"type": "base64", "media_type": "image/png",
         "data": "iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAQAAAC1HAwCAAAAC0lEQVR42mNkYAAAAAYAAjCB0C8AAAAASUVORK5CYII="}}
      ]
    }]
  }'

Expected

Model receives the image bytes and describes it (or at minimum reports back that it was received).

Actual

The model's thinking output says:

"looking at the input, I don't actually see an image - I see the text [Image: but no actual image content loaded"

usage.input_tokens is 23 — far below what a real image would add — confirming the base64 payload never reaches the model. The image block appears to be replaced by a text placeholder during the Anthropic → Ollama format conversion.

Notes

• The same Kimi model works fine with images when used through Moonshot's own Anthropic endpoint, so the model itself is not the issue.
• Ollama's own OpenAI-compatibility layer (/v1/chat/completions) handles images correctly for other vision models, which suggests the Anthropic layer's request translator is just missing the image → images[] mapping.
• DeepWiki's Anthropic compatibility layer doc lists image blocks as a recognized type in MessagesRequest but does not indicate whether they are actively processed — this report confirms they are not.

Suggested fix

In the Anthropic compatibility translator, when a user message contains an image content block of type: "base64", the base64 data should be appended to the images array of the corresponding Ollama /api/chat message (or stored in the multimodal buffer for vision models), instead of being stringified into a [Image: placeholder.