Fine-tuning abstractive summarization models requires high-quality annotated data. However, obtaining such corpora is expensive and time-consuming, as it requires human annotators to read and comprehend long documents to create accurate summaries. Active learning mitigates this issue by selecting only the most informative instances for annotation, allowing models to achieve competitive results with significantly fewer labels. However, the application of active learning to summarization remains under-explored, and existing studies often suffer from instability and significant computational bottlenecks. To overcome these challenges, we propose LOBSTER (LOss-BaSed acTivE leaRning), a novel active learning framework designed specifically for abstractive summarization. LOBSTER improves performance by prioritizing unlabeled instances semantically similar to the model's current high-loss training examples, enabling the model to explicitly correct its specific weaknesses. Our empirical evaluation across three benchmark datasets and two summarization backbone models demonstrates that LOBSTER consistently matches or outperforms current state-of-the-art approaches while achieving a query selection speedup of up to 665x.
Figures & tables
Figure 1: The three-stage pipeline of LOBSTER. (1) Loss-based Hard Example Selection identifies “Hard Example” set H (red squares) via high cross-entropy loss to serve as semantic anchors. (2) Representative Candidate Filtering uses IDDS to distill a pool of representative candidates (green circles) from the unlabeled set U . (3) Semantic Hardness Projection computes the Max-Similarity Score S(xu) (Eq. 3) using Sentence-BERT embeddings. This helps to identify a “semantic twin” for each hard example, forming the final Top- B batch for annotation.
Figure 2: Number of labeled instances vs. ROUGE-1. Comparison of active strategies using BART and PEGASUS backbones on AESLC, XSum, and CNN/DM datasets.
Avg. Selection Time (s)
Model
Dataset
BAS
DUAL
IDDS
LOBSTER
BART-base
AESLC
46.1
38.7
0.02
0.6
XSum
66.6
63.7
0.4
0.8
CNN/DM
70.2
69.2
0.3
0.8
PEGASUS-large
AESLC
221.1
113.6
0.01
1.0
XSum
390.0
267.6
0.4
1.5
Table 1: Average runtime (in seconds) for instance selection, for one active learning iteration, across different strategies. Comparison across backbones and datasets.
Appendix figures & tables11 assets
Supplementary material from the paper’s appendix.
Appendix
Dataset
Subset
# Ins.
Doc. len.
Sum. len.
Gigaword
Train
200
39.6
11.2
Test
1K
38.3
10.4
AESLC
Train
14,436
115.3
4
Test
1,906
114.6
4.1
XSum
Train
204,045
388.6
23.1
Test
1K
384.3
23
Appendix
Table 2: Statistics for the datasets used in this work. We report the number of instances (# Ins.) and the average length of source documents (Doc. len.) and summaries (Sum. len.) for both training and test splits.
Hyperparameter
BART-base
PEGASUS-large
Learning Rate
2e−5
5e−5
Batch Size (Train)
16
8
Batch Size (Eval)
32
16
Num. Epochs
6
4
Optimizer
AdamW
AdamW
Weight Decay
0.028
0.03
Appendix
Table 3: Hyperparameters used for fine-tuning the backbone summarization models.
Model
Method
ROUGE-1
ROUGE-2
ROUGE-L
BERTScore
Dataset: AESLC
BART-base
Random
26.6 ± 0.65
13.2 ± 0.65
26.0 ± 0.63
13.51 ± 0.57
BAS
26.5 ± 0.17
13.1 ± 0.31
25.8 ± 0.24
13.63 ± 0.99
IDDS
27.0 ± 0.32
12.5 ± 0.32
25.4 ± 0.31
13.03 ± 0.19
DUAL
26.9 ± 0.86
13.2 ± 0.70
26.0 ± 0.85
12.95 ± 0.14
LOBSTER
27.1 ± 0.88
13.4 ± 0.45
26.3 ± 0.80
12.96 ± 0.65
Appendix
Table 4: Summarization performance (ROUGE and rescaled BERTScore) with a 150-instance annotation budget. Results are reported as mean ± standard deviation. The best performance for each metric and dataset is highlighted in bold.
LOBSTER vs. Baseline ( p -value)
Dataset
Model
DUAL
Random
IDDS
BAS
ROUGE-1
AESLC
BART-base
0.1681
0.4250
0.0083 ∗↑
0.0203 ∗↑
PEGASUS-large
< 0.001 ∗↑
< 0.001 ∗↑
0.5113
< 0.001 ∗↑
XSum
BART-base
0.0224 ∗↓
0.1649
0.6326
0.2942
PEGASUS-large
0.2192
0.8924
< 0.001 ∗↑
0.2532
Appendix
Table 5: Paired permutation test p-values comparing LOBSTER against baseline methods at the 150-instance annotation budget for ROUGE-1 and BERTScore. An asterisk (*) indicates a statistically significant difference ( p<0.05 ). For significant results, arrows indicate whether LOBSTER scored significantly higher ( ↑ ) or lower ( ↓ ) than the baseline.
Dataset
Setup
ROUGE (1 / 2 / L)
BERTScore
AESLC
Llama-3-8B-Instruct (Zero-shot)
27.16 / 12.06 / 25.22
11.61
BART-base + LOBSTER
27.10 / 13.40 / 26.30
12.96
PEGASUS-large + LOBSTER
22.10 / 10.90 / 21.50
0 7.66
XSum
Llama-3-8B-Instruct (Zero-shot)
29.41 / 0 8.40 / 21.20
29.13
BART-base + LOBSTER
32.50 / 10.60 / 25.30
37.00
PEGASUS-large + LOBSTER
43.50 / 20.30 / 35.00
47.72
Appendix
Table 6: Performance comparison of models fine-tuned using examples selected by LOBSTER (at a 150-instance annotation budget) against a zero-shot Llama-3-8B-Instruct baseline. Bold values indicate the best performance for each metric within each dataset.
Model
Dataset
Active Learning
LOBSTER
DUAL
BAS
IDDS
Rand.
BART-base
AESLC
1900
1900
1300
—
2000
XSum
2000
1700
1700
—
1600
CNN/DM
50
60
110
100
100
PEGASUS-large
AESLC
1800
1800
2000
2000
1800
XSum
80
90
80
100
80
Appendix
Table 7: Data Efficiency Analysis: Number of annotated samples required to reach 90% of the full-dataset performance. Bold values indicate the winning strategy for each configuration, and a dash (—) indicates that the configuration failed to reach the 90% target.
Avg Selection time (s)
Model
Dataset
BAS
DUAL
IDDS
LOBSTER
BART-base
AESLC
61.8
366.2
0.3
3.9
XSum
96.1
560.5
2.8
12.1
CNN/DM
70.2
69.2
0.3
0.8
PEGASUS-large
AESLC
164.6
618.1
0.3
12.8
XSum
390.0
267.6
0.4
1.5
Appendix
Table 8: Data Efficiency Analysis: Average runtime (in seconds) for instance selection, for one active learning iteration, across different strategies. Comparison across backbones and datasets.
Figure 3: Number of labeled instances vs. rescaled BERTScore. Comparison of active strategies using BART and PEGASUS backbones on AESLC, XSum, and CNN/DM datasets.
Figure 4: Number of labeled instances vs. ROUGE-1. Comparison of active learning strategies using BART and PEGASUS backbones on AESLC, XSum, and CNN/DM datasets. The dashed horizontal line in each subplot denotes the 90% performance threshold of the full-dataset baseline.
Figure 5: Number of labeled instances vs. BERTScore. Comparison of LOBSTER and the LOBSTER (Random Anchors) ablation using BART and PEGASUS backbones on AESLC, XSum, and CNN/DM datasets.
Figure 6: Impact of IDDS on Selection Diversity (PCA visualization of selected instances). Comparison of the proposed LOBSTER method with IDDS versus the ablation without IDDS. The IDDS module prevents semantic collapse by filtering redundant candidates, leading to higher ROUGE-1 scores.
Automatic text summarization has become increasingly important due to the rapid growth of digital textual information. This paper presents a Multi-Model Summarization Framework designed to improve the robustness and quality of abstractive text summarization. Relying on a single model often leads to inconsistent summarization quality across articles with varying structures and topics. To address this limitation, the proposed framework integrates multiple fine-tuned transformer-based summarization models and introduces a metric-based selection mechanism. In this framework, each model independently generates a candidate summary for the same input article. The generated summaries are then evaluated using automatic evaluation metrics that capture both lexical similarity and semantic relevance. Based on these scores, the framework selects the highest-quality summary as the final output. The models are fine-tuned and evaluated on the widely used CNN/DailyMail news summarization dataset. Experimental results demonstrate that the proposed framework achieves the highest BERTScore among all compared methods with a score of 88.63%. It also outperforms several LLMs such as GPT3-D2, Falcon-7b, and Mpt-7b, highlighting its effectiveness and robustness. These findings highlight the effectiveness of leveraging multiple transformer-based models within a metric-based selection strategy to improve the quality and robustness of automatic text summarization systems.
Ahmed Alansary, Ali Hamdi
Faculty of Computer Science · MSA University · Giza, Egypt
Abstractive summarization requires models to generate summaries that convey information in the source document. While large language models can generate summaries without fine-tuning, they often miss key details and include extraneous information. We propose BLooP (Bigram Lookahead Promotion), a simple training-free decoding intervention that encourages large language models (LLMs) to generate tokens that form bigrams from the source document. BLooP operates through a hash table lookup at each decoding step, requiring no training, fine-tuning, or model modification. We demonstrate improvements in ROUGE and BARTScore for Llama-3.1-8B-Instruct, Mistral-Nemo-Instruct-2407, and Gemma-2-9b-it on CNN/DM, CCSum, Multi-News, and SciTLDR. Human evaluation shows that BLooP significantly improves faithfulness without reducing readability. We make the code available at https://github.com/varuniyer/BLooP
Abstractive text summarization is the technique of generating a short and concise summary comprising the salient ideas of a source text without making a subset of the salient sentences from the source text. The introduction of transformer models such as BART, T5, and PEGASUS has made this sort of summarization process more efficient and accurate. The objective of this paper is to fine-tune PEGASUS on the XL-Sum English corpus to achieve a better performance compared to the baseline mT5 model. The performance of the generated summaries from the fine-tuned model is evaluated using the ROUGE metric, which basically compares the auto-generated summaries with human-created summaries. To the best of our knowledge, the results from our fine-tuned PEGASUS model give a state-of-the-art performance on the XL-Sum English Corpus. To quantify the improvement, there is a 4.04% improvement in the ROUGE-1 score, a 15.25% increase in the ROUGE-2 score, and a 3.39% improvement in the ROUGE-L score from the baseline model.
Sadiul Arefin Rafi, Naimur Rahman, Kazi Nazibul Islam +2