Swift-1.5-4bit-MLX / FULL_MAC_VALIDATION.md
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Bound retained server cache while keeping prompt reuse enabled (#1)
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Full Swift Mac cache validation — 2026-09-25

Both complete, existing Swift checkpoints passed native Metal text generation and two cached follow-up requests on an AWS M4 Pro Mac with 48 GiB RAM. All weight shards were verified against their recorded SHA-256 hashes before loading. No quantization, tensor edits, context changes or manual memory-limit overrides were performed. Hub offline mode was enabled during testing.

The input is our own synthetic repeated-record conversation, followed by a short request to reply READY. It is a memory/cache regression test, not a quality benchmark, an exact reproduction of another person's conversation, or a claim that every context fits. The follow-ups must reuse at least half the prompt to pass; the test fails if the worker dies or the retained-cache budget is exceeded.

Checkpoint Initial prompt tokens First request, seconds Follow-ups, seconds Follow-up cached tokens Peak MLX allocation, GiB
4-bit 86,004 893.64 1.46, 1.42 86000, 86020 31.57
5-bit 86,004 907.00 1.45, 1.45 86000, 86020 34.79

The first request includes model loading and initial prompt processing. MLX peak allocation is not total process or system memory. Complete request results, generated replies, cache limits and sampled swap observations are recorded in compatibility/cache-tests/full-mac-4bit-results.json and compatibility/cache-tests/full-mac-5bit-results.json.

Environment: macOS 26.7 (25G229), Python 3.12.13, MLX 0.32.2, MLX-LM 0.32.0, Transformers 5.14.1, Hugging Face Hub 1.31.0. Official MLX-LM base revision: c69d1288440a0dc4e6401fc417098b07598dccd5. The shared runtime uses the existing Swift architecture patch, its 5-bit support extension, and the unchanged server-cache patch. The 5-bit extension also accepts the original 4-bit format. The cache defaults are two retained entries, automatic byte budgeting, one prompt/decode stream, and 512-token prefill steps.

To reproduce, install the pinned environment and all three patches in the order documented by the 5-bit release, then use a complete local snapshot. Run one model at a time on an Apple Silicon Mac with at least 48 GiB RAM:

HF_HUB_OFFLINE=1 TRANSFORMERS_OFFLINE=1 python \
  Swift-1.5-4bit-MLX/compatibility/cache-tests/validate_full_mac_cache.py \
  --snapshot Swift-1.5-4bit-MLX --output full-mac-4bit-results
HF_HUB_OFFLINE=1 TRANSFORMERS_OFFLINE=1 python \
  Swift-1.5-5bit-MLX/compatibility/cache-tests/validate_full_mac_cache.py \
  --snapshot Swift-1.5-5bit-MLX --output full-mac-5bit-results

Output directories must be new. The harness uses the real server and complete released weights, without building or quantizing any synthetic model. It suppresses the server startup helper's wired-limit call. The unchanged stock BatchGenerator still calls MLX's set_wired_limit with Apple's recommended working-set size; macOS memory settings are not changed. The legacy result field memory_limit_overrides=false denotes no manual override, not suppression of this normal batch-generator behavior. The actual Metal device is recorded in the results.

These results establish the tested text workload on the stated 48 GiB machine. They do not establish 24 GiB operation, arbitrary 262k-token workloads, GUI/plugin integration, image/video chat, speculative MTP generation, or broad output quality. Existing installations still need to apply the runtime patch and restart the server. The recorded checks are independently executed tests, not a hosted CI status.