PrismML released Bonsai 27B, a low-bit compression of Qwen3.6 27B shipped in two variants, and the headline claim is that a 27B-class model now fits and runs on a phone. The ternary variant constrains weights to minus one, zero, and plus one with FP16 group-wise scaling, landing at 1.71 effective bits per weight and 5.9 GB. The 1-bit variant uses binary weights and reaches 1.125 effective bits per weight at 3.9 GB, small enough for an iPhone 17 Pro. What distinguishes this from the usual quantization release is that the low-bit representation runs end-to-end — embeddings, attention, MLPs, and the LM head — with no higher-precision escape hatches anywhere in the stack. The vision tower ships separately in 4-bit. Context is 262K, speculative decoding is supported, and the whole thing is Apache 2.0.
Across a fifteen-benchmark suite in thinking mode, the ternary build retains 95% of the full-precision baseline and the 1-bit build 90%. In aggregate the numbers are Qwen3.6 at 85.0, ternary at 80.5, and 1-bit at 76.1. The degradation is not uniform, and where it concentrates is the interesting part. Agentic and tool-calling work — BFCL v3 and TauBench — falls from 80.0 to 74.0 to 66.0, and vision — MMMU Pro and OCRBench — falls from 72.6 to 65.2 to 59.6. So the 1-bit variant gives up fourteen points precisely on tool use. Throughput is 163 tokens per second for 1-bit and 134 for ternary on an RTX 5090; 87 and 58 respectively on an M5 Max. PrismML claims an intelligence density of 0.53 per GB, more than ten times the full-precision baseline and roughly 2.7 times the best competing low-bit build.
The caveats deserve equal billing. Every benchmark here is vendor-reported, and the "most aggressive conventional low-bit build" it measures itself against is never named, which makes the 2.7x claim unfalsifiable as published. The tool-calling collapse sits awkwardly against the post's own framing of agentic workloads as the target use case — the variant that fits the phone is the variant worst at the thing phones would plausibly want. The phone demonstration itself is labeled "Demo Mode: Cached and Prefilled Image Context," which is not the same as live inference. And the 12 GB iPhone reportedly exposes only about 6 GB to any single app, shared with KV cache and activations, so a 3.9 GB weight file is closer to the ceiling than the number suggests. Still, sub-1.2 bits per weight end-to-end with 90% retention is a real result, and the Apache 2.0 license means the claims are checkable by anyone willing to run the suite.
- PrismML frames the contribution as intelligence density — 0.53 per GB, over 10x the FP baseline.
- Hacker News (613 points, 214 comments) centered on whether the phone demo's cached-and-prefilled context undercuts the on-device claim.
- Commenters flagged the 14-point tool-calling drop as the buried lede for anyone targeting agentic workloads.