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abstract indexed · arXiv 2609.17475 · updated 2026-10-18

JustFit: 200K-Token LLM Serving on a 24 GiB Laptop with Just-in-Time State Management

First page of JustFit: 200K-Token LLM Serving on a 24 GiB Laptop with Just-in-Time State Management
From the original paper · arXiv 2609.17475Page 1. Select the image to read the PDF.

JustFit replaces the standard mlx-vlm runtime's eager KV allocation and full-component residency with just-in-time materialization, compressed KV execution, and state-preserving transitions, independent of weight quantization. The cost is a specialized MLX-based runtime restricted to Apple Silicon, added systems complexity in state lifecycle management, and reliance on MXFP4-class compressed execution whose latency at long contexts (19.11 tokens/s at 32K input) is modest. Failure modes include reconstruction or swap errors corrupting long reasoning chains, degraded throughput under multi-request contention, and fragility outside the tested Qwen/MLX stack, with the AIME result serving as anecdotal rather than systematic quality evidence.

For solo builders

A possible application for this research area. Paper-specific feasibility still needs a full-paper review.

Your inference service slows down when several customers send requests together.

What you would change

Replay a recorded request trace with only the proposed serving policy changed.

Try the idea on your product

A proposed first test. Set your budget and success criteria before running it.

Replay a recorded request trace with only the proposed serving policy changed.

Compare against

Your current scheduler on the same model and hardware.

  1. Locate the paper's implementation and check its license, model support, data needs, and hardware requirements. Stop here if you cannot obtain the required artifacts.
  2. Save a small set of representative product tasks and expected outcomes. Keep evaluation tasks out of any training or tuning, and choose quality and cost limits before running.
  3. Run the baseline and the proposed change on identical inputs. Keep other settings fixed and repeat paired runs to expose variation.
  4. Save per-task outputs, failures, timings, and all usage costs. Review regressions before expanding the test.

What to measure

Requests meeting your latency target, throughput, failures, and cost per successful request.

When to keep it

Keep the change only if it meets your preselected quality and latency limits and improves the metric you care about after setup and operating costs. Otherwise retain the baseline. This is an exploration plan, not a validated recommendation.

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minimum test setup
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published evidence setup
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source-linked claims
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exposure checks
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Why it was shortlisted

The technical change, research area, and reason it entered the archive.

recommendation
test
research area
serving and batching
technical change
Just-in-time KV and state management for long-context local serving
published
2026-09-15

The 6.93x context gain on exactly the reader's hardware class is compelling, but the runtime is MLX/Apple-Silicon-specific, early-stage, and lacks independent validation, so it warrants a workload-specific pilot rather than production adoption.

About the technical core

Equations have not been fetched yet.

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Inspect the original paper

Claims and evidence

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  1. claim 01Paperraft inference
    Read the brief interpretation

    JustFit replaces the standard mlx-vlm runtime's eager KV allocation and full-component residency with just-in-time materialization, compressed KV execution, and state-preserving transitions, independent of weight quantization. The cost is a specialized MLX-based runtime restricted to Apple Silicon, added systems complexity in state lifecycle management, and reliance on MXFP4-class compressed execution whose latency at long contexts (19.11 tokens/s at 32K input) is modest. Failure modes include reconstruction or swap errors corrupting long reasoning chains, degraded throughput under multi-request contention, and fragility outside the tested Qwen/MLX stack, with the AIME result serving as anecdotal rather than systematic quality evidence.

    This is a Paperraft inference. It is not pinned to a verified PDF passage.

    Inspect the source
  2. claim 02Paperraft inference

    Completed single-request context rises from 30,720 to 212,992 positions (6.93x) on a 24 GiB M4 Pro running Qwen3.8-27B MXFP4, with 19.11 tokens/s on a 32K-input probe and a median peak footprint of 16,374 MiB.

    This is a Paperraft inference. It is not pinned to a verified PDF passage.

    Inspect the source

Exposure map

Author findings, Paperraft interpretations, and the next check. Missing analysis never counts as evidence of safety.

quality

Still unknown

Which tasks improve, and which regress against the baseline?

compute and memory

Still unknown

What memory, hardware, and total compute does the complete method require?

latency

Still unknown

Are startup time, typical response time, and slow requests measured separately?

operations

Still unknown

What must be monitored, maintained, and rolled back?

software compatibility

Still unknown

Does the implementation support your model, runtime, and hardware?

security

Still unknown

What new data access, permissions, or trust boundaries does it introduce?

data and training

Still unknown

What data preparation or training is required, and is it included in the cost?

reproducibility

Still unknown

Are code, versions, inputs, and evaluation scripts available?

Continue the investigation

A reading guide for serving and batching.

Editorial prompts, not findings from this paper or a validated test plan. Detailed analysis is still pending for the topics below.

What to inspect

What arrival pattern, concurrency, and context lengths drive the reported result?

Plan a fair comparison

Can you replay one request trace and compare throughput, tail latency, failures, and total cost?

Questions for adoption

Does the method still meet your latency target during bursts and with mixed request lengths?

Read the paper with these questions

Inside the paper

Preview the first 3 pages of the original PDF. Click the stack to turn the page.

The downloadable skill includes SKILL.md and evidence.json, with recorded findings and unanswered checks. TRY-IT.md adds a product test plan and a blank results sheet.

A reading aid for your agent. Findings still need validation.

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Provisional research brief updated 2026-10-18. Paperraft has not reproduced this experiment.

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arXiv 2609.17475

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