Posts in category: OpenAI

Live demos and discussions at our virtual booth.OpenAI

OpenAI released its first commercial product back in June: an API for developers to access advanced technologies for building new applications and services. The API features a powerful general purpose language model, GPT-3, and has received tens of thousands of applications to date.

In addition to offering GPT-3 and future models via the OpenAI API, and as part of a multiyear partnership announced last year, OpenAI has agreed to license GPT-3 to Microsoft for their own products and services. The deal has no impact on continued access to the GPT-3 model through OpenAI’s API, and existing and future users of it will continue building applications with our API as usual.

Unlike most AI systems which are designed for one use-case, OpenAI’s API today provides a general-purpose “text in, text out” interface, allowing users to try it on virtually any English language task. GPT-3 is the most powerful model behind the API today, with 175 billion parameters. There are several other models available via the API today, as well as other technologies and filters that allow developers to customize GPT-3 and other language models for their own use.

Today, the API remains in a limited beta as OpenAI and academic partners test and assess the capabilities and limitations of these powerful language models. To learn more about the API or to sign up for the beta, please visit beta.openai.com.

OpenAI

Large-scale language models are becoming increasingly capable on NLP tasks. These models are usually trained with the objective of next word prediction on a dataset of human-written text. But this objective doesn’t capture exactly what we want; usually, we don’t want our models to imitate humans, we want them to give high-quality answers. This mismatch is clear when a model is trained to imitate low-quality human-written text, but it can also happen in more subtle ways. For example, a model trained to predict what a human would say might make up facts when it is unsure, or generate sentences reflecting harmful social bias, both failure modes that have been well-documented.

As part of our work on safety, we want to develop techniques that align our models’ objectives with the end behavior we really care about. As our models become more powerful, we believe aligning them with our goals will be very important to ensure they are beneficial for humans. In the short term, we wanted to test if human feedback techniques could help our models improve performance on useful tasks.

We focused on English text summarization, as it’s a challenging problem where the notion of what makes a “good summary” is difficult to capture without human input. We apply our method primarily to an existing dataset of posts submitted to the social network Reddit^[1] together with human-written “TL;DRs,” which are short summaries written by the original poster.

We first train a reward model via supervised learning to predict which summaries humans will prefer.^[2] We then fine-tune a language model with reinforcement learning (RL) to produce summaries that score highly according to that reward model. We find that this significantly improves the quality of the summaries, as evaluated by humans, even on datasets very different from the one used for fine-tuning.

Our approach follows directly from our previous work on learning from human feedback. There has also been other work on using human feedback to train summarization models. We push the technique further by scaling to larger models, collecting more feedback data, closely monitoring researcher-labeler agreement, and providing frequent feedback to labelers. Human feedback has also been used to train models in several other domains, such as dialogue, semantic parsing, translation, story and review generation, evidence extraction, and more traditional RL tasks.

Results

We evaluated several different summarization models—some pre-trained on a broad distribution of text from the internet, some fine-tuned via supervised learning to predict TL;DRs, and some fine-tuned using human feedback.^[3] To evaluate each model, we had it summarize posts from the validation set and asked humans to compare their summaries to the human-written TL;DR. The results are shown in Figure 1.

We found that RL fine-tuning with human feedback had a very large effect on quality compared to both supervised fine-tuning and scaling up model size. In particular, our 1.3 billion parameter (1.3B) model trained with human feedback outperforms our 12B model trained only with supervised learning. Summaries from both our 1.3B and 6.7B human feedback models are preferred by our labelers to the original human-written TL;DRs in the dataset.^[4]

People make different trade-offs when writing summaries, including between conciseness and coverage of the original text; depending on the purpose of the summary, different summary lengths might be preferred. Our labelers tended to prefer longer summaries, so our models adapted to that preference and converged to the longest allowable length. Controlling for length reduced human preferences for our 6.7B model’s summaries from 70% to 65%, explaining a minority of our gains.^[5]

Transfer results

Human feedback models trained on Reddit transfer to generate excellent summaries of CNN/DM news articles without further training

To test our models’ generalization, we also applied them directly to the popular CNN/DM news dataset. These articles are more than twice as long as Reddit posts and are written in a very different style. Our models have seen news articles during pre-training, but all of our human data and RL fine-tuning was on the Reddit TL;DR dataset.

This time we evaluated our models by asking our labelers to rate them on a scale from 1–7.^[7] We discovered that our human feedback models transfer to generate excellent short summaries of news articles without any training. When controlling for summary length, our 6.7B human feedback model generates summaries that are rated higher than the CNN/DM reference summaries written by humans. This suggests that our human feedback models have learned something more general about how to summarize text, and are not specific to Reddit posts.

Approach

Our core method consists of four steps: training an initial summarization model, assembling a dataset of human comparisons between summaries, training a reward model to predict the human-preferred summary, and then fine-tuning our summarization models with RL to get a high reward.

We trained several supervised baselines by starting from GPT-style transformer models trained on text from the Internet, and fine-tuning them to predict the human-written TL;DR via supervised learning. We mainly use models with 1.3 and 6.7 billion parameters. As a sanity check, we confirmed that this training procedure led to competitive results^[8] on the CNN/DM dataset.

We then collected a dataset of human quality judgments. For each judgment, a human compares two summaries of a given post and picks the one they think is better.^[9] We use this data to train a reward model that maps a (post, summary) pair to a reward r. The reward model is trained to predict which summary a human will prefer, using the rewards as logits.

Finally, we optimize the policy against the reward model using RL. We use PPO with 1 million episodes in total, where each episode consists of the policy summarizing a single article and then receiving a reward r. We include a KL penalty that incentivizes the policy to remain close to the supervised initialization.

Collecting data from humans

Any training procedure that uses human feedback is directly influenced by the actual humans labeling the data. In our previous work on fine-tuning language models from human preferences, our labelers often gave high ratings to summaries we thought were average, which was reflected in the quality of our trained models.

In response, in this project we invested heavily in ensuring high data quality. We hired about 80 contractors using third-party vendor sites,^[10] and paid them an hourly wage regardless of the number of summaries evaluated.^[11] Hiring contractors rather than relying on crowdsourcing websites allowed us to maintain a hands-on relationship with labelers: we created an onboarding process, developed a website with a customizable labeler interface, answered questions in a shared chat room, and had one-on-one video calls with labelers. We also made sure to clearly communicate our definition of summary quality, after spending significant time reading summaries ourselves, and we carefully monitored agreement rates between us and labelers throughout the project.

Optimizing the reward model

Optimizing our reward model eventually leads to sample quality degradation

Optimizing against our reward model is supposed to make our policy align with human preferences. But the reward model is only a proxy for human preferences, as it only sees a small amount of comparison data from a narrow distribution of summaries. While the reward model performs well on the kinds of summaries it was trained on, we wanted to know how much we could optimize against it until it started giving useless evaluations.

We trained policies at different “optimization strengths” against the reward model, and asked our labelers to evaluate the summaries from these models. We did this by varying the KL coefficient, which trades off the incentive to get a higher reward against the incentive to remain close to the initial supervised policy. We found the best samples had roughly the same predicted reward as the 99th percentile of reference summaries from the dataset. Eventually optimizing the reward model actually makes things worse.

Limitations

If we have a well-defined notion of the desired behavior for a model, our method of training from human feedback allows us to optimize for this behavior. However, this is not a method for determining what the desired model behavior should be. Deciding what makes a good summary is fairly straightforward, but doing this for tasks with more complex objectives, where different humans might disagree on the correct model behavior, will require significant care. In these cases, it is likely not appropriate to use researcher labels as the “gold standard”; rather, individuals from groups that will be impacted by the technology should be included in the process to define “good” behavior, and hired as labelers to reinforce this behavior in the model.

We trained on the Reddit TL;DR dataset because the summarization task is significantly more challenging than on CNN/DM. However, since the dataset consists of user-submitted posts with minimal moderation, they sometimes contain content that is offensive or reflects harmful social biases. This means our models can generate biased or offensive summaries, as they have been trained to summarize such content.

Part of our success involves scaling up our reward model and policy size. This requires a large amount of compute, which is not available to all researchers: notably, fine-tuning our 6.7B model with RL required about 320 GPU-days. However, since smaller models trained with human feedback can exceed the performance of much larger models, our procedure is more cost-effective than simply scaling up for training high-quality models on specific tasks.

Though we outperform the human-written reference summaries on TL;DR, our models have likely not reached human-level performance, as the reference summary baselines for TL;DR and CNN/DM are not the highest possible quality. When evaluating our model’s TL;DR summaries on a 7-point scale along several axes of quality (accuracy, coverage, coherence, and overall), labelers find our models can still generate inaccurate summaries, and give a perfect overall score 45% of the time.^[12] For cost reasons, we also do not directly compare to using a similar budget to collect high-quality demonstrations, and training on those using standard supervised fine-tuning.

Future directions

We’re interested in scaling human feedback to tasks where humans can’t easily evaluate the quality of model outputs. For example, we might want our models to answer questions that would take humans a lot of research to verify; getting enough human evaluations to train our models this way would take a long time. One approach to tackle this problem is to give humans tools to help them evaluate more quickly and accurately. If these tools use ML, we can also improve them with human feedback, which could allow humans to accurately evaluate model outputs for increasingly complicated tasks.

In addition to tackling harder problems, we’re also exploring different types of feedback beyond binary comparisons: we can ask humans to provide demonstrations, edit model outputs to make them better, or give explanations as to why one model output is better than another. We’d like to figure out which kinds of feedback are most effective for training models that are aligned with human preferences.

If you are interested in working on these research questions, we’re hiring!

OpenAI

Our third class of OpenAI Scholars presented their final projects at virtual Demo Day, showcasing their research results from over the past five months. These projects investigated problems such as analyzing how GPT-2 represents grammar, measuring the interpretability of models trained on Coinrun, and predicting epileptic seizures using brain recordings. More information about the next class of Scholars and how to apply will be announced this fall.

The OpenAI Scholars program provides stipends and mentorship to individuals from underrepresented groups to study deep learning and open-source a project.

Our Scholars have demonstrated core technical skills across various expert domains and self-motivation—critical competencies for a self-directed program like this one. They each entered the field of machine learning as relative newcomers, and we hope their progress shows how accessible machine learning is.

Learn more about our Scholars program.

Diversity is core to AI having a positive effect on the world—it’s necessary to ensure the advanced AI systems in the future are built to benefit everyone.

If you’re excited to begin your own journey into ML, check out some of our educational materials. More information about the next class of scholars and how to apply will be announced this fall. Stay tuned!

Huge thanks to Microsoft for providing Azure compute credits to scholars, to our mentors for their time and commitment, and to all the supporters that made this program possible.

OpenAI

We find that, just as a large transformer model trained on language can generate coherent text, the same exact model trained on pixel sequences can generate coherent image completions and samples. By establishing a correlation between sample quality and image classification accuracy, we show that our best generative model also contains features competitive with top convolutional nets in the unsupervised setting.

CodeICML 2020 Paper (v1)Paper (v2)

Introduction

Unsupervised and self-supervised learning, or learning without human-labeled data, is a longstanding challenge of machine learning. Recently, it has seen incredible success in language, as transformer models like BERT, GPT-2, RoBERTa, T5, and other variants have achieved top performance on a wide array of language tasks. However, the same broad class of models has not been successful in producing strong features for image classification. Our work aims to understand and bridge this gap.

Transformer models like BERT and GPT-2 are domain agnostic, meaning that they can be directly applied to 1-D sequences of any form. When we train GPT-2 on images unrolled into long sequences of pixels, which we call iGPT, we find that the model appears to understand 2-D image characteristics such as object appearance and category. This is evidenced by the diverse range of coherent image samples it generates, even without the guidance of human provided labels. As further proof, features from the model achieve state-of-the-art performance on a number of classification datasets and near state-of-the-art unsupervised accuracy^[1] on ImageNet.

To highlight the potential of generative sequence modeling as a general purpose unsupervised learning algorithm, we deliberately use the same transformer architecture as GPT-2 in language. As a consequence, we require significantly more compute in order to produce features competitive with those from top unsupervised convolutional nets. However, our results suggest that when faced with a new domain where the correct model priors are unknown, a large GPT-2 can learn excellent features without the need for domain-specific architectural design choices.

Completions

Favorites

Animals

Painted Landscapes

Sports

Architecture

ImageNet-R

Movie Posters

Famous Artworks

Popular Memes

Landscapes

Album Covers

Common English Words

US & State Flags

OpenAI Research Covers

OpenAI Pets

OpenAI Cooking

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Model Input

Completions right

Original

Model-generated completions of human-provided half-images. We sample the remaining halves with temperature 1 and without tricks like beam search or nucleus sampling. While we showcase our favorite completions in the first panel, we do not cherry-pick images or completions in all following panels.

Samples

View more samples

Model-generated image samples. We sample these images with temperature 1 and without tricks like beam search or nucleus sampling. All of our samples are shown, with no cherry-picking. Nearly all generated images contain clearly recognizable objects.

From language GPT to image GPT

In language, unsupervised learning algorithms that rely on word prediction (like GPT-2 and BERT) have been extremely successful, achieving top performance on a wide array of language tasks. One possible reason for this success is that instances of downstream language tasks appear naturally in text: questions are often followed by answers (which could help with question-answering) and passages are often followed by summaries (which could help with summarization). In contrast, sequences of pixels do not clearly contain labels for the images they belong to.

Even without this explicit supervision, there is still a reason why GPT-2 on images might work: a sufficiently large transformer trained on next pixel prediction might eventually learn to generate diverse^[2] samples with clearly recognizable objects. Once it learns to do so, an idea known as “Analysis by Synthesis”^[3] suggests that the model will also know about object categories. Many early generative models were motivated by this idea, and more recently, BigBiGAN was an example which produced encouraging samples and features. In our work, we first show that better generative models achieve stronger classification performance. Then, through optimizing GPT-2 for generative capabilities, we achieve top-level classification performance in many settings, providing further evidence for analysis by synthesis.

Towards general unsupervised learning

Generative sequence modeling is a universal unsupervised learning algorithm: since all data types can be represented as sequences of bytes, a transformer can be directly applied to any data type without additional engineering. Our work tests the power of this generality by directly applying the architecture used to train GPT-2 on natural language to image generation. We deliberately chose to forgo hand coding any image specific knowledge in the form of convolutions or techniques like relative attention, sparse attention, and 2-D position embeddings.

As a consequence of its generality, our method requires significantly more compute to achieve competitive performance in the unsupervised setting. Indeed, contrastive methods are still the most computationally efficient methods for producing high quality features from images. However, in showing that an unsupervised transformer model is competitive with the best unsupervised convolutional nets, we provide evidence that it is possible to trade off hand coded domain knowledge for compute. In new domains, where there isn’t much knowledge to hand code, scaling compute seems an appropriate technique to test.

Approach

We train iGPT-S, iGPT-M, and iGPT-L, transformers containing 76M, 455M, and 1.4B parameters respectively, on ImageNet. We also train iGPT-XL^[4], a 6.8 billion parameter transformer, on a mix of ImageNet and images from the web. Due to the large computational cost of modeling long sequences with dense attention, we train at the low resolutions of 32×32, 48×48, and 64×64.

While it is tempting to work at even lower resolutions to further reduce compute cost, prior work has demonstrated that human performance on image classification begins to drop rapidly below these sizes. Instead, motivated by early color display palettes, we create our own 9-bit color palette to represent pixels. Using this palette yields an input sequence length 3 times shorter than the standard (R, G, B) palette, while still encoding color faithfully.

Experimental results

There are two methods we use to assess model performance, both of which involve a downstream classification task. The first, which we refer to as a linear probe, uses the trained model to extract features^[5] from the images in the downstream dataset, and then fits a logistic regression to the labels. The second method fine-tunes^[6] the entire model on the downstream dataset.

Since next pixel prediction is not obviously relevant to image classification, features from the final layer may not be the most predictive of the object category. Our first result shows that feature quality is a sharply increasing, then mildly decreasing function of depth. This behavior suggests that a transformer generative model operates in two phases: in the first phase, each position gathers information from its surrounding context in order to build a contextualized image feature. In the second phase, this contextualized feature is used to solve the conditional next pixel prediction task. The observed two stage performance of our linear probes is reminiscent of another unsupervised neural net, the bottleneck autoencoder, which is manually designed so that features in the middle are used.

Our next result establishes the link between generative performance and feature quality. We find that both increasing the scale of our models and training for more iterations result in better generative performance, which directly translates into better feature quality.

When we evaluate our features using linear probes on CIFAR-10, CIFAR-100, and STL-10, we outperform features from all supervised and unsupervised transfer algorithms. Our results are also compelling in the full fine-tuning setting.

Given the resurgence of interest in unsupervised and self-supervised learning on ImageNet, we also evaluate the performance of our models using linear probes on ImageNet. This is an especially difficult setting, as we do not train at the standard ImageNet input resolution. Nevertheless, a linear probe on the 1536 features from the best layer of iGPT-L trained on 48×48 images yields 65.2% top-1 accuracy, outperforming AlexNet.

Contrastive methods typically report their best results on 8192 features, so we would ideally evaluate iGPT with an embedding dimension of 8192 for comparison. However, training such a model is prohibitively expensive, so we instead concatenate features from multiple layers as an approximation. Unfortunately, our features tend to be correlated across layers, so we need more of them to be competitive. Taking 15360 features from 5 layers in iGPT-XL yields 72.0% top-1 accuracy, outperforming AMDIM, MoCo, and CPC v2, but still underperforming SimCLR by a decent margin.

Because masked language models like BERT have outperformed generative models on most language tasks, we also evaluate the performance of BERT on our image models. Instead of training our model to predict the next pixel given all preceding pixels, we mask out 15% of the pixels and train our model to predict them from the unmasked ones. We find that though linear probe performance on BERT models is significantly worse, they excel during fine-tuning:

While unsupervised learning promises excellent features without the need for human-labeled data, significant recent progress has been made under the more forgiving framework of semi-supervised learning, which allows for limited amounts of human-labeled data. Successful semi-supervised methods often rely on clever techniques such as consistency regularization, data augmentation, or pseudo-labeling, and purely generative-based approaches have not been competitive for years. We evaluate iGPT-L^[7] on a competitive benchmark for this sub-field and find that a simple linear probe on features from non-augmented images outperforms Mean Teacher and MixMatch, though it underperforms FixMatch.

Limitations

While we have shown that iGPT is capable of learning powerful image features, there are still significant limitations to our approach. Because we use the generic sequence transformer used for GPT-2 in language, our method requires large amounts of compute: iGPT-L was trained for roughly 2500 V100-days while a similarly performing MoCo model can be trained in roughly 70 V100-days.

Relatedly, we model low resolution inputs using a transformer, while most self-supervised results use convolutional-based encoders which can easily consume inputs at high resolution. A new architecture, such as a domain-agnostic multiscale transformer, might be needed to scale further. Given these limitations, our work primarily serves as a proof-of-concept demonstration of the ability of large transformer-based language models to learn excellent unsupervised representations in novel domains, without the need for hardcoded domain knowledge. However, the significant resource cost to train these models and the greater accuracy of convolutional neural-network based methods precludes these representations from practical real-world applications in the vision domain.

Finally, generative models can exhibit biases that are a consequence of the data they’ve been trained on. Many of these biases are useful, like assuming that a combination of brown and green pixels represents a branch covered in leaves, then using this bias to continue the image. But some of these biases will be harmful, when considered through a lens of fairness and representation. For instance, if the model develops a visual notion of a scientist that skews male, then it might consistently complete images of scientists with male-presenting people, rather than a mix of genders. We expect that developers will need to pay increasing attention to the data that they feed into their systems and to better understand how it relates to biases in trained models.

Conclusion

We have shown that by trading off 2-D knowledge for scale and by choosing predictive features from the middle of the network, a sequence transformer can be competitive with top convolutional nets for unsupervised image classification. Notably, we achieved our results by directly applying the GPT-2 language model to image generation. Our results suggest that due to its simplicity and generality, a sequence transformer given sufficient compute might ultimately be an effective way to learn excellent features in many domains.

If you’re excited to work with us on this area of research, we’re hiring!

OpenAI

We’re releasing an API for accessing new AI models developed by OpenAI. Unlike most AI systems which are designed for one use-case, the API today provides a general-purpose “text in, text out” interface, allowing users to try it on virtually any English language task. You can now request access in order to integrate the API into your product, develop an entirely new application, or help us explore the strengths and limits of this technology.

Given any text prompt, the API will return a text completion, attempting to match the pattern you gave it. You can “program” it by showing it just a few examples of what you’d like it to do; its success generally varies depending on how complex the task is. The API also allows you to hone performance on specific tasks by training on a dataset (small or large) of examples you provide, or by learning from human feedback provided by users or labelers.

We’ve designed the API to be both simple for anyone to use but also flexible enough to make machine learning teams more productive. In fact, many of our teams are now using the API so that they can focus on machine learning research rather than distributed systems problems. Today the API runs models with weights from the GPT-3 family with many speed and throughput improvements. Machine learning is moving very fast, and we’re constantly upgrading our technology so that our users stay up to date.

The field’s pace of progress means that there are frequently surprising new applications of AI, both positive and negative. We will terminate API access for obviously harmful use-cases, such as harassment, spam, radicalization, or astroturfing. But we also know we can’t anticipate all of the possible consequences of this technology, so we are launching today in a private beta rather than general availability, building tools to help users better control the content our API returns, and researching safety-relevant aspects of language technology (such as analyzing, mitigating, and intervening on harmful bias). We’ll share what we learn so that our users and the broader community can build more human-positive AI systems.

In addition to being a revenue source to help us cover costs in pursuit of our mission, the API has pushed us to sharpen our focus on general-purpose AI technology—advancing the technology, making it usable, and considering its impacts in the real world. We hope that the API will greatly lower the barrier to producing beneficial AI-powered products, resulting in tools and services that are hard to imagine today.

Interested in exploring the API? Join companies like Algolia, Quizlet, and Reddit, and researchers at institutions like the Middlebury Institute in our private beta.

OpenAI

Procgen Competition

Sign up for Procgen

The Procgen Competition focuses on improving sample efficiency and generalization in reinforcement learning. Participants will attempt to maximize agents’ performance using a fixed number of environment interactions. Agents will be evaluated in each of the 16 environments already publicly released in Procgen Benchmark, as well as in four secret test environments created specifically for this competition. By aggregating performance across so many diverse environments, we obtain high quality metrics to judge the underlying algorithms. More information about the details of each round can be found here.

Since all content is procedurally generated, each Procgen environment intrinsically requires agents to generalize to never-before-seen situations. These environments therefore provide a robust test of an agent’s ability to learn in many diverse settings. Moreover, we designed Procgen environments to be fast and simple to use. Participants with limited computational resources will be able to easily reproduce our baseline results and run new experiments. We hope that this will empower participants to iterate quickly on new methods to improve sample efficiency and generalization in RL.

MineRL Competition

Sign up for MineRL

Many of the recent, celebrated successes of artificial intelligence, such as AlphaStar, AlphaGo, and our own OpenAI Five, utilize deep reinforcement learning to achieve human or super-human level performance in sequential decision-making tasks. These improvements to the state-of-the-art have thus far required an exponentially increasing amount of compute and simulator samples, and therefore it is difficult^[1] to apply many of these systems directly to real-world problems where environment samples are expensive. One well-known way to reduce the environment sample complexity is to leverage human priors and demonstrations of the desired behavior.

To further catalyze research in this direction, we are co-organizing the MineRL 2020 Competition which aims to foster the development of algorithms which can efficiently leverage human demonstrations to drastically reduce the number of samples needed to solve complex, hierarchical, and sparse environments. To that end, participants will compete to develop systems which can obtain a diamond in Minecraft from raw pixels using only 8,000,000 samples from the MineRL simulator and 4 days of training on a single GPU machine. Participants will be provided the MineRL-v0 dataset (website, paper), a large-scale collection of over 60 million frames of human demonstrations, enabling them to utilize expert trajectories to minimize their algorithm’s interactions with the Minecraft simulator.

This competition is a follow-up to the MineRL 2019 Competition in which the top team’s agent was able to obtain an iron pickaxe (the penultimate goal of the competition) under this extremely limited compute and simulator-interaction budget. Put in perspective, state-of-the-art standard reinforcement learning systems require hundreds of millions of environment interactions on large multi-GPU systems to achieve the same goal. This year, we anticipate competitors will push the state-of-the-art even further.

To guarantee that competitors develop truly sample efficient algorithms, the MineRL competition organizers train the top team’s final round models from scratch with strict constraints on the hardware, compute, and simulator-interaction available. The MineRL 2020 Competition also features a novel measure to avoid hand engineering features and overfitting solutions to the domain. More details on the competition structure can be found here.

OpenAI

We’re releasing an analysis showing that since 2012 the amount of compute needed to train a neural net to the same performance on ImageNet classification has been decreasing by a factor of 2 every 16 months. Compared to 2012, it now takes 44 times less compute to train a neural network to the level of AlexNet (by contrast, Moore’s Law would yield an 11x cost improvement over this period). Our results suggest that for AI tasks with high levels of recent investment, algorithmic progress has yielded more gains than classical hardware efficiency.

Algorithmic improvement is a key factor driving the advance of AI. It’s important to search for measures that shed light on overall algorithmic progress, even though it’s harder than measuring such trends in compute.

44x less compute required to get to AlexNet performance 7 years later

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Measuring efficiency

Algorithmic efficiency can be defined as reducing the compute needed to train a specific capability. Efficiency is the primary way we measure algorithmic progress on classic computer science problems like sorting. Efficiency gains on traditional problems like sorting are more straightforward to measure than in ML because they have a clearer measure of task difficulty.^[1] However, we can apply the efficiency lens to machine learning by holding performance constant. Efficiency trends can be compared across domains like DNA sequencing (10-month doubling), solar energy (6-year doubling), and transistor density (2-year doubling).

For our analysis, we primarily leveraged open-source re-implementations to measure progress on AlexNet level performance over a long horizon. We saw a similar rate of training efficiency improvement for ResNet-50 level performance on ImageNet (17-month doubling time). We saw faster rates of improvement over shorter timescales in Translation, Go, and Dota 2:

1. Within translation, the Transformer surpassed seq2seq performance on English to French translation on WMT’14 with 61x less training compute 3 years later.
2. We estimate AlphaZero took 8x less compute to get to AlphaGoZero level performance 1 year later.
3. OpenAI Five Rerun required 5x less training compute to surpass OpenAI Five (which beat the world champions, OG) 3 months later.

It can be helpful to think of compute in 2012 not being equal to compute in 2019 in a similar way that dollars need to be inflation-adjusted over time. A fixed amount of compute could accomplish more in 2019 than in 2012. One way to think about this is that some types of AI research progress in two stages, similar to the “tick tock” model of development seen in semiconductors; new capabilities (the “tick”) typically require a significant amount of compute expenditure to obtain, then refined versions of those capabilities (the “tock”) become much more efficient to deploy due to process improvements.

Increases in algorithmic efficiency allow researchers to do more experiments of interest in a given amount of time and money. In addition to being a measure of overall progress, algorithmic efficiency gains speed up future AI research in a way that’s somewhat analogous to having more compute.

Other measures of AI progress

In addition to efficiency, many other measures shed light on overall algorithmic progress in AI. Training cost in dollars is related, but less narrowly focused on algorithmic progress because it’s also affected by improvement in the underlying hardware, hardware utilization, and cloud infrastructure. Sample efficiency is key when we’re in a low data regime, which is the case for many tasks of interest. The ability to train models faster also speeds up research and can be thought of as a measure of the parallelizability of learning capabilities of interest. We also find increases in inference efficiency in terms of GPU time, parameters, and flops meaningful, but mostly as a result of their economic implications^[2] rather than their effect on future research progress. Shufflenet achieved AlexNet-level performance with an 18x inference efficiency increase in 5 years (15-month doubling time), which suggests that training efficiency and inference efficiency might improve at similar rates. The creation of datasets/​environments/​benchmarks is a powerful method of making specific AI capabilities of interest more measurable.

Primary limitations

1. We have only a small number of algorithmic efficiency data points on a few tasks. It’s unclear the degree to which the efficiency trends we’ve observed generalize to other AI tasks. Systematic measurement could make it clear whether an algorithmic equivalent to Moore’s Law^[3] in the domain of AI exists, and if it exists, clarify its nature. We consider this a highly interesting open question. We suspect we’re more likely to observe similar rates of efficiency progress on similar tasks. By similar tasks, we mean tasks within these sub-domains of AI, on which the field agrees we’ve seen substantial progress, and that have comparable levels of investment (compute and/or researcher time).
2. Even though we believe AlexNet represented a lot of progress, this analysis doesn’t attempt to quantify that progress. More generally, the first time a capability is created, algorithmic breakthroughs may have reduced the resources required from totally infeasible^[4] to merely high. We think new capabilities generally represent a larger share of overall conceptual progress than observed efficiency increases of the type shown here.
3. This analysis focuses on the final training run cost for an optimized model rather than total development costs. Some algorithmic improvements make it easier to train a model by making the space of hyperparameters that will train stably and get good final performance much larger. On the other hand, architecture searches increase the gap between the final training run cost and total training costs.
4. We don’t speculate^[5] on the degree to which we expect efficiency trends will extrapolate in time, we merely present our results and discuss the implications if the trends persist.

Measurement and AI policy

We believe that policymaking related to AI will be improved by a greater focus on the measurement and assessment of AI systems, both in terms of technical attributes and societal impact. We think such measurement initiatives can shed light on important questions in policy; our AI and Compute analysis suggests policymakers should increase funding for compute resources for academia, so that academic research can replicate, reproduce, and extend industry research. This efficiency analysis suggests that policymakers could develop accurate intuitions about the cost of deploying AI capabilities—and how these costs are going to alter over time—by more closely assessing the rate of improvements in efficiency for AI systems.

Tracking efficiency going forward

If large scale compute continues to be important to achieving state of the art (SOTA) overall performance in domains like language and games then it’s important to put effort into measuring notable progress achieved with smaller amounts of compute (contributions often made by academic institutions). Models that achieve training efficiency state of the arts on meaningful capabilities are promising candidates for scaling up and potentially achieving overall top performance. Additionally, figuring out the algorithmic efficiency improvements are straightforward^[6] since they are just a particularly meaningful slice of the learning curves that all experiments generate.

We also think that measuring long run trends in efficiency SOTAs will help paint a quantitative picture of overall algorithmic progress. We observe that hardware and algorithmic efficiency gains are multiplicative and can be on a similar scale over meaningful horizons, which suggests that a good model of AI progress should integrate measures from both.

Our results suggest that for AI tasks with high levels of investment (researcher time and/or compute) algorithmic efficiency might outpace gains from hardware efficiency (Moore’s Law). Moore’s Law was coined in 1965 when integrated circuits had a mere 64 transistors (6 doublings) and naively extrapolating it out predicted personal computers and smartphones (an iPhone 11 has 8.5 billion transistors). If we observe decades of exponential improvement in the algorithmic efficiency of AI, what might it lead to? We’re not sure. That these results make us ask this question is a modest update for us towards a future with powerful AI services and technology.

For all these reasons, we’re going to start tracking efficiency SOTAs publicly. We’ll start with vision and translation efficiency benchmarks (ImageNet^[7] and WMT14), and we’ll consider adding more benchmarks over time. We believe there are efficiency SOTAs on these benchmarks we’re unaware of and encourage the research community to submit them here (we’ll give credit to original authors and collaborators).

Industry leaders, policymakers, economists, and potential researchers are all trying to better understand AI progress and decide how much attention they should invest and where to direct it. Measurement efforts can help ground such decisions. If you’re interested in this type of work, consider applying to work at OpenAI’s Foresight or Policy team!

OpenAI

Motivation and prior work

Automatic music generation dates back to more than half a century. A prominent approach is to generate music symbolically in the form of a piano roll, which specifies the timing, pitch, velocity, and instrument of each note to be played. This has led to impressive results like producing Bach chorals, polyphonic music with multiple instruments, as well as minute long musical pieces.

But symbolic generators have limitations—they cannot capture human voices or many of the more subtle timbres, dynamics, and expressivity that are essential to music. A different approach^[1] is to model music directly as raw audio. Generating music at the audio level is challenging since the sequences are very long. A typical 4-minute song at CD quality (44 kHz, 16-bit) has over 10 million timesteps. For comparison, GPT-2 had 1,000 timesteps and OpenAI Five took tens of thousands of timesteps per game. Thus, to learn the high level semantics of music, a model would have to deal with extremely long-range dependencies.

One way of addressing the long input problem is to use an autoencoder that compresses raw audio to a lower-dimensional space by discarding some of the perceptually irrelevant bits of information. We can then train a model to generate audio in this compressed space, and upsample back to the raw audio space.

We chose to work on music because we want to continue to push the boundaries of generative models. Our previous work on MuseNet explored synthesizing music based on large amounts of MIDI data. Now in raw audio, our models must learn to tackle high diversity as well as very long range structure, and the raw audio domain is particularly unforgiving of errors in short, medium, or long term timing.

Raw audio 44.1k samples per second, where each sample is a float that represents the amplitude of sound at that moment in time

Encode using CNNs (convolutional neural networks)

Compressed audio 344 samples per second, where each sample is 1 of 2048 possible vocab tokens

Generate novel patterns from trained transformer conditioned on lyrics

Novel compressed audio 344 samples per second

Upsample using transformers and decode using CNNs

Novel raw audio 44.1k samples per second

Approach

Compressing music to discrete codes

Jukebox’s autoencoder model compresses audio to a discrete space, using a quantization-based approach called VQ-VAE. Hierarchical VQ-VAEs can generate short instrumental pieces from a few sets of instruments, however they suffer from hierarchy collapse due to use of successive encoders coupled with autoregressive decoders. A simplified variant called VQ-VAE-2 avoids these issues by using feedforward encoders and decoders only, and they show impressive results at generating high-fidelity images.

We draw inspiration from VQ-VAE-2 and apply their approach to music. We modify their architecture as follows:

• To alleviate codebook collapse common to VQ-VAE models, we use random restarts where we randomly reset a codebook vector to one of the encoded hidden states whenever its usage falls below a threshold.
• To maximize the use of the upper levels, we use separate decoders and independently reconstruct the input from the codes of each level.
• To allow the model to reconstruct higher frequencies easily, we add a spectral loss that penalizes the norm of the difference of input and reconstructed spectrograms.

We use three levels in our VQ-VAE, shown below, which compress the 44kHz raw audio by 8x, 32x, and 128x, respectively, with a codebook size of 2048 for each level. This downsampling loses much of the audio detail, and sounds noticeably noisy as we go further down the levels. However, it retains essential information about the pitch, timbre, and volume of the audio.

1. Compress

2. Generate

Each VQ-VAE level independently encodes the input. The bottom level encoding produces the highest quality reconstruction, while the top level encoding retains only the essential musical information.

To generate novel songs, a cascade of transformers generates codes from top to bottom level, after which the bottom-level decoder can convert them to raw audio.

Generating codes using transformers

Next, we train the prior models whose goal is to learn the distribution of music codes encoded by VQ-VAE and to generate music in this compressed discrete space. Like the VQ-VAE, we have three levels of priors: a top-level prior that generates the most compressed codes, and two upsampling priors that generate less compressed codes conditioned on above.

The top-level prior models the long-range structure of music, and samples decoded from this level have lower audio quality but capture high-level semantics like singing and melodies. The middle and bottom upsampling priors add local musical structures like timbre, significantly improving the audio quality.

We train these as autoregressive models using a simplified variant of Sparse Transformers. Each of these models has 72 layers of factorized self-attention on a context of 8192 codes, which corresponds to approximately 24 seconds, 6 seconds, and 1.5 seconds of raw audio at the top, middle and bottom levels, respectively.

Once all of the priors are trained, we can generate codes from the top level, upsample them using the upsamplers, and decode them back to the raw audio space using the VQ-VAE decoder to sample novel songs.

Dataset

To train this model, we crawled the web to curate a new dataset of 1.2 million songs (600,000 of which are in English), paired with the corresponding lyrics and metadata from LyricWiki. The metadata includes artist, album genre, and year of the songs, along with common moods or playlist keywords associated with each song. We train on 32-bit, 44.1 kHz raw audio, and perform data augmentation by randomly downmixing the right and left channels to produce mono audio.

Artist and genre conditioning

The top-level transformer is trained on the task of predicting compressed audio tokens. We can provide additional information, such as the artist and genre for each song. This has two advantages: first, it reduces the entropy of the audio prediction, so the model is able to achieve better quality in any particular style; second, at generation time, we are able to steer the model to generate in a style of our choosing.

This t-SNE below shows how the model learns, in an unsupervised way, to cluster similar artists and genres close together, and also makes some surprising associations like Jennifer Lopez being so close to Dolly Parton!

Lyrics conditioning

In addition to conditioning on artist and genre, we can provide more context at training time by conditioning the model on the lyrics for a song. A significant challenge is the lack of a well-aligned dataset: we only have lyrics at a song level without alignment to the music, and thus for a given chunk of audio we don’t know precisely which portion of the lyrics (if any) appear. We also may have song versions that don’t match the lyric versions, as might occur if a given song is performed by several different artists in slightly different ways. Additionally, singers frequently repeat phrases, or otherwise vary the lyrics, in ways that are not always captured in the written lyrics.

To match audio portions to their corresponding lyrics, we begin with a simple heuristic that aligns the characters of the lyrics to linearly span the duration of each song, and pass a fixed-size window of characters centered around the current segment during training. While this simple strategy of linear alignment worked surprisingly well, we found that it fails for certain genres with fast lyrics, such as hip hop. To address this, we use Spleeter to extract vocals from each song and run NUS AutoLyricsAlign on the extracted vocals to obtain precise word-level alignments of the lyrics. We chose a large enough window so that the actual lyrics have a high probability of being inside the window.

To attend to the lyrics, we add an encoder to produce a representation for the lyrics, and add attention layers that use queries from the music decoder to attend to keys and values from the lyrics encoder. After training, the model learns a more precise alignment.

Limitations

While Jukebox represents a step forward in musical quality, coherence, length of audio sample, and ability to condition on artist, genre, and lyrics, there is a significant gap between these generations and human-created music.

For example, while the generated songs show local musical coherence, follow traditional chord patterns, and can even feature impressive solos, we do not hear familiar larger musical structures such as choruses that repeat. Our downsampling and upsampling process introduces discernable noise. Improving the VQ-VAE so its codes capture more musical information would help reduce this. Our models are also slow to sample from, because of the autoregressive nature of sampling. It takes approximately 9 hours to fully render one minute of audio through our models, and thus they cannot yet be used in interactive applications. Using techniques that distill the model into a parallel sampler can significantly speed up the sampling speed. Finally, we currently train on English lyrics and mostly Western music, but in the future we hope to include songs from other languages and parts of the world.

Future directions

Our audio team is continuing to work on generating audio samples conditioned on different kinds of priming information. In particular, we’ve seen early success conditioning on MIDI files and stem files. Here’s an example of a raw audio sample conditioned on MIDI tokens. We hope this will improve the musicality of samples (in the way conditioning on lyrics improved the singing), and this would also be a way of giving musicians more control over the generations. We expect human and model collaborations to be an increasingly exciting creative space. If you’re excited to work on these problems with us, we’re hiring.

As generative modeling across various domains continues to advance, we are also conducting research into issues like bias and intellectual property rights, and are engaging with people who work in the domains where we develop tools. To better understand future implications for the music community, we shared Jukebox with an initial set of 10 musicians from various genres to discuss their feedback on this work. While Jukebox is an interesting research result, these musicians did not find it immediately applicable to their creative process given some of its current limitations. We are connecting with the wider creative community as we think generative work across text, images, and audio will continue to improve. If you’re interested in being a creative collaborator to help us build useful tools or new works of art in these domains, please let us know!

To connect with the corresponding authors, please email jukebox@openai.com.

OpenAI