Is Flash Attention 2 mandatory?

[anr2me]

Since flash_attn is imported in qwen2_navit.py without checking is_flash_attn_2_available() like in other .py files, does it mean Flash Attention package need to be installed?

If Flash Attention is mandatory, you might want mentioned it in Readme file. But it would be nice if Flash Attention is being optional.

[fengyifu2000]

Thanks for your interest and feedback. In our training and inference pipeline, Flash Attention is indeed treated as a required dependency. We will add it to the dependency list and clarify this in the README.

[anr2me]

I see. No need to add flash-attn as dependency, just mention about it in Readme should be sufficient, since FA2 will need to be build from source first (which could take long), as some people might prefer to install a pre-built FA2 wheel from third-party.

[fengyifu2000]

Thanks! That is a good suggestion！

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From: ***@***.***> Date: Thu, May 21, 2026, 20:20 Subject: Re: [bytedance/Lance] Is Flash Attention 2 mandatory? (Issue #14) To: ***@***.***> Cc: ***@***.***>, ***@***.***> [image]anr2me left a comment (bytedance/Lance#14)<#14 (comment)> I see. No need to add flash-attn as dependency, just mention about it in Readme should be sufficient, since FA2 will need to be build from source first (which could take long), as some people might prefer to install a pre-built FA2 wheel from third-party. — Reply to this email directly, view it on GitHub<#14 (comment)>, or unsubscribe<https://github.com/notifications/unsubscribe-auth/CD5KRLG7BBB6ZWGXZON54ML433YAXAVCNFSM6AAAAACZHH4AQSVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHM2DKMBYGE4TONJXHA>. Triage notifications on the go with GitHub Mobile for iOS<https://apps.apple.com/app/apple-store/id1477376905?ct=notification-email&mt=8&pt=524675> or Android<https://play.google.com/store/apps/details?id=com.github.android&referrer=utm_campaign%3Dnotification-email%26utm_medium%3Demail%26utm_source%3Dgithub>. You are receiving this because you commented.[image]Message ID: ***@***.***>