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Published equation contexts

CSAE  ≈  2 d (n+k) TC_{\mathrm{SAE}} \;\approx\; 2\,d\,(n + k)\,T

Why this formula appears here

Work out what that architecture actually spends compute on per token, because the two halves of it behave differently. The encoding step needs a score for every one of the n candidate latents before it can select the top k , so it is an unavoidably dense matrix multiply: roughly 2dn floating-point operations. The decoding step only touches the k latents that survived, so it is sparse: roughly 2dk operations. Summed and multiplied across T training tokens, a first-order compute model for training the dictionary is CSAE  ≈  2 d (n+k) TC_{\mathrm{SAE}} \;\approx\; 2\,d\,(n + k)\,T . Because published TopK configurations keep k in the tens to low hundreds while n runs into the millions, n ≫\gg k and the encoding term dominates almost…

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CSAEC_{\mathrm{SAE}}

Symbol C_SAE

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dd

Symbol d

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nn

Symbol n

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TT

Symbol T

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Published contexts (1)

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CSAE  ≈  2 d (n+k) T.C_{\mathrm{SAE}} \;\approx\; 2\,d\,(n + k)\,T .

Equation 14 · AI Research

What Interpretability Actually Costs to Do at Scale

This equation gives an approximation: it relates the quantities while allowing an approximation.

Work out what that architecture actually spends compute on per token, because the two halves of it behave differently. The encoding step needs a score for every one of the n candidate latents before it can select the top k , so it is an unavoidably dense matrix multiply: roughly 2dn floating-point operations. The decoding step only touches the k latents that survived, so it is sparse: roughly 2dk operations. Summed and multiplied across T training tokens, a first-order compute model for training the dictionary is CSAE  ≈  2 d (n+k) TC_{\mathrm{SAE}} \;\approx\; 2\,d\,(n + k)\,T . Because published TopK configurations keep k in the tens to low hundreds while n runs into the millions, n ≫\gg k and the encoding term dominates almost…

Meanings in this article

  • kk: the because published topk configurations keep.
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