ollama - 💡(How to fix) Fix gemma4:26b thinking mode causes passive/incomplete tool-calling behavior on CUDA via /v1/chat/completions

Description

When using gemma4:26b with thinking enabled (chat_template_kwargs: {"thinking": true}) via the OpenAI-compatible /v1/chat/completions endpoint on a Linux CUDA backend, the model reads files correctly but fails to follow through with subsequent tool calls (e.g. writing code). Instead it produces a brief conversational summary and asks "How can I help?" — effectively becoming passive mid-task.

Environment

• OS: Linux (WSL2)
• GPU: RTX 5090
• Ollama version: 0.20.4
• Model: gemma4:26b (Q4_K_M)
• Endpoint: /v1/chat/completions
• Thinking: enabled, reasoning_effort: low

Steps to Reproduce

1. Pull gemma4:26b
2. Enable thinking mode via chat_template_kwargs: {"thinking": true}
3. Use the /v1/chat/completions endpoint in an agentic loop with tools defined
4. Ask the model to perform a multi-step task (e.g. clone a repo, then add a new API endpoint to a file)

Expected Behavior

Model completes agentic tasks end-to-end — reads files, writes code, uses tools — as observed on macOS Metal with identical Ollama version, model, and thinking settings.

Actual Behavior

Model reads a file via tool call, summarizes the contents, then responds conversationally asking for further instructions instead of proceeding with the requested task. Subsequent tool calls (e.g. write_file) are never made.

Workaround

Disabling thinking ("thinking": false) restores correct agentic behavior on CUDA.

Notes

The same setup (identical Ollama version 0.20.4, same model tag, same thinking settings, same harness and prompts) works correctly on macOS Metal (Apple M-series, Mac Mini 64GB RAM). This points to a platform-specific difference in how thinking output is handled on CUDA vs Metal.

Related to #15288 (thinking output routed to reasoning field on /v1/chat/completions).