GoKawiilTested Kimi K3 for Coding
Jul 18, 2026
The new model Kimi K3 was released this week, and it is claimed to be near-frontier level quality similar to Fable and GPT. I decided to try it out and see if it could optimize my Rust program. I felt a less specific task, like "optimize this function somehow" was a good test.
Kimi K3
I set up Kimi K3 in OpenCode, and made a copy of my program directory so that I could throw away the changes made easily. I directed a prompt to the function I wanted optimized. I had spent a fair amount of time optimizing this function, and I did not seem to be making much progress on my own.
Kimi K3 had 2 recommendations, and I decided to have it pursue the SWAR optimization—SIMD Within a Register. With SWAR , a single 64-bit value is treated as 8 eight-bit values—so we can handle 8 u8 values (single-byte) at once.
Kimi K3 took about 15 minutes for the task, and it completed it perfectly. I found the optimization sped up the program by 2%. So Kimi K3 both decided on an appropriate optimization, and implemented it with no errors—it seems to me that Kimi K3 could well be a frontier-level model as advertised. It cost about $1 for the tokens on OpenRouter.