[Xet] Document adaptive concurrency for xet transfers

[rajatarya]

Summary

• Document that hf_xet uses adaptive concurrency by default, dynamically adjusting parallelism based on real-time network conditions (default: 1→64 streams)
• Update HF_XET_HIGH_PERFORMANCE=1 docs to reflect it now raises adaptive concurrency bounds (initial=16, max=124) and increases buffer sizes, rather than setting fixed values
• Add HF_XET_FIXED_DOWNLOAD_CONCURRENCY / HF_XET_FIXED_UPLOAD_CONCURRENCY as documented escape hatches for advanced users
• Add adaptive concurrency notes to the xet upload and download protocol specs

Files changed

File	Change
docs/hub/models-downloading.md	Rewrite "Faster downloads" section
docs/hub/mlx.md	Add brief explanation of HP mode
docs/hub/xet/using-xet-storage.md	Update recommendations with adaptive concurrency + fixed concurrency env vars
docs/xet/upload-protocol.md	Add paragraph on adaptive concurrency in "Ordering and Concurrency"
docs/xet/download-protocol.md	Add bullet on adaptive concurrency under "Parallel downloads"

Test plan

• Verify doc build passes in CI
• Confirm env var names match xet-core source (HF_XET_HIGH_PERFORMANCE, HF_XET_FIXED_DOWNLOAD_CONCURRENCY, HF_XET_FIXED_UPLOAD_CONCURRENCY)
• Confirm default values (initial=1, max=64) and HP values (initial=16, min=4, max=124) match xet_config/src/groups/client.rs and xet_config/src/xet_config.rs

🤖 Generated with Claude Code

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Note

Low Risk
Documentation-only changes describing hf_xet/xet-core transfer behavior and new/updated environment-variable guidance; no code or runtime behavior is modified.

Overview
Documents that hf_xet uses adaptive concurrency by default for Xet transfers, and updates download guidance to clarify that HF_XET_HIGH_PERFORMANCE=1 raises concurrency bounds and buffer sizes (intended for high-bandwidth machines with �64GB RAM).

Expands using-xet-storage.md with a dedicated Environment Variables section (including fixed-concurrency escape hatches via HF_XET_FIXED_{DOWNLOAD,UPLOAD}_CONCURRENCY) and adds adaptive-concurrency notes to the Xet upload/download protocol specs; also adds a brief HP-mode note to the MLX Hub guide.

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[rajatarya]

@julien-c : (not urgent, can wait until you are back.)

[hoytak]

LGTM!

[julien-c]

nice!

let's communicate widely when this is shipped, as it's very cool feature for power users and casual users alike

[HuggingFaceDocBuilderDev]

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