What is the strongest open source model for coding against Opus 4.6?

I’ve been using Qwen3-72B (and even the smaller 32B model) extensively alongside Opus 4.6 for the past few weeks.

My takeaway is that while Opus 4.6 still holds the edge in high-level system design and 'knowing what it doesn't know,' Qwen3 is remarkably competitive in Python and Rust implementations. In fact, for specific LeetCode-style logic or boilerplate generation, Qwen3 often feels faster and more concise.

The real strength of Qwen3 is its instruction-following capability—it rarely hallucinates API signatures compared to other open-source models I've tried. If you have the hardware to run the 72B (or even a high-quantized version), it's probably the closest you'll get to the Opus experience in the open-source world right now.

GLM 5 perhaps. But you need good hardware.

And it’s open weight. Not open source.