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FASTopic: Pretrained Transformer is a Fast, Adaptive, Stable, and Transferable Topic Model
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Proposes FASTopic, a fast topic model that reconstructs document-word relations via pretrained Transformer document embeddings and learnable topic/word embeddings, regularized with entropic optimal transport plans (ETP).
Problem
Existing topic models lack efficiency, effectiveness, or stability: VAE-based models are slow and complex, clustering-based models yield repetitive topics and poor doc-topic distributions, and neural models are hyperparameter-sensitive.
Approach
Dual Semantic-relation Reconstruction (DSR) models doc-topic and topic-word distributions as relations between document, topic and word embeddings and reconstructs the BoW through them; Embedding Transport Plan (ETP) regularizes these relations as entropic optimal transport plans (Sinkhorn) with learnable topic and word weights to avoid the relation bias of parameterized softmax.
Key results
- FASTopic achieves C_V 0.426 and TD 0.983 on 20NG and the best topic quality on all six datasets in the reported table, versus ECRTM as the strongest baseline.
- FASTopic runs in 10.6s on 20NG versus 365.4s for ECRTM and 58.6s for LDA-Mallet, and completes all datasets within about 1 minute (12.5s on NYT, 60.3s on ACL).
- Ablation replacing ETP with parameterized softmax drops 20NG C_V from 0.426 to 0.368 and TD from 0.983 to 0.391.
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| Use ETP instead of parameterized softmax for semantic relations (ablation) | FASTopic · 20NG | TD: 0.391 -> 0.983 | Helped |
| Use ETP instead of parameterized softmax for semantic relations (ablation) | FASTopic · 20NG | C_V: 0.368 -> 0.426 | Helped |
| Use ETP instead of parameterized softmax for semantic relations (ablation) | FASTopic · 20NG | Purity: 0.401 -> 0.577 | Helped |
| Use ETP instead of parameterized softmax for semantic relations (ablation) | FASTopic · 20NG | NMI: 0.452 -> 0.525 | Helped |
| Use ETP instead of parameterized softmax for semantic relations (ablation) | FASTopic · NYT | C_V: 0.363 -> 0.437 | Helped |
| Use ETP instead of parameterized softmax for semantic relations (ablation) | FASTopic · NYT | TD: 0.338 -> 0.999 | Helped |
| Use ETP instead of parameterized softmax for semantic relations (ablation) | FASTopic · WoS | C_V: 0.395 -> 0.457 | Helped |
| Use ETP instead of parameterized softmax for semantic relations (ablation) | FASTopic · WoS | TD: 0.522 -> 1.000 | Helped |
| Use ETP instead of parameterized softmax for semantic relations (ablation) | FASTopic · NeurIPS | C_V: 0.380 -> 0.422 | Helped |
| Use ETP instead of parameterized softmax for semantic relations (ablation) | FASTopic · NeurIPS | TD: 0.216 -> 0.998 | Helped |
| Use ETP instead of parameterized softmax for semantic relations (ablation) | FASTopic · ACL | C_V: 0.373 -> 0.420 | Helped |
| Use ETP instead of parameterized softmax for semantic relations (ablation) | FASTopic · ACL | TD: 0.164 -> 0.998 | Helped |
Surprising findings
- Parameterized softmax suffers a relation bias issue where most topic embeddings collapse together, causing repetitive topics even with only 10 topics.
- Using pretrained word embeddings like word2vec or GloVe is avoided because they are not in the same semantic space as document embeddings.
Limitations
- Bounded by the maximum input length of pretrained document embedding models, which may hurt extremely long documents.
- Relies on the quality of the pretrained document embedding model; performance varies with the embedding model choice.
Experimental setup
Datasets: 20NG NYT WoS NeurIPS ACL Wikitext-103
Benchmarks: 20NG NYT WoS NeurIPS ACL Wikitext-103
Metrics: C_V topic diversity Purity NMI running time classification accuracy F1
Baselines: LDA-Mallet NMF BERTopic CombinedTM GINopic ProGBN HyperMiner ECRTM
Builds on: ECRTM Sinkhorn algorithm Sentence-BERT
Closest papers by meaning
- Context-guided Embedding Adaptation for Effective Topic Modeling in Low-Resource Regimes (NeurIPS 2023 · similarity 0.88)
- Neural Topic Model via Optimal Transport (ICLR 2021 · similarity 0.87)
- OTLDA: A Geometry-aware Optimal Transport Approach for Topic Modeling (NeurIPS 2020 · similarity 0.86)
- Sparse Autoencoders are Topic Models (ICML 2026 · similarity 0.86)
- How Do Transformers Learn Topic Structure: Towards a Mechanistic Understanding (ICML 2023 · similarity 0.86)
- On the Affinity, Rationality, and Diversity of Hierarchical Topic Modeling (AAAI 2024 · similarity 0.85)
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